diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,37 @@
 # Revision history for dataframe
 
+## 0.4.0.0
+* `readSeparated` no longer takes the separator as an argument. This is not placed into readOptions.
+* Some improvements to the synthesis demo
+* Add a `declareColumnsParquetFile` function. 
+* Column conversion functions now take expressions instead of strings.
+* Add more monadic functions to make previously tricky transformations easier to write:
+    ```haskell
+    {-# LANGUAGE OverloadedStrings #-}
+    {-# LANGUAGE TemplateHaskell #-}
+
+    module Main where
+
+    import qualified DataFrame as D
+    import qualified DataFrame.Functions as F
+
+    import DataFrame.Monad
+
+    import Data.Text (Text)
+    import DataFrame.Functions ((.&&), (.>=))
+
+    $(F.declareColumnsFromCsvFile "./data/housing.csv")
+
+    main :: IO ()
+    main = do
+        df <- D.readCsv "./data/housing.csv"
+        print $ execFrameM df $ do
+            is_expensive <- deriveM "is_expensive" (median_house_value .>= 500000)
+            meanBedrooms <- inspectM (D.meanMaybe total_bedrooms)
+            totalBedrooms <- imputeM total_bedrooms meanBedrooms
+            filterWhereM (totalBedrooms .>= 200 .&& is_expensive)
+    ```
+
 ## 0.3.5.0
 * Add a `deriveWithExpr` that returns an expression that you can use in a subsequent expressions.
 * Add `declareColumnsFromCsvFile` which can create the expressions up front for use in scripts.
diff --git a/dataframe.cabal b/dataframe.cabal
--- a/dataframe.cabal
+++ b/dataframe.cabal
@@ -1,6 +1,6 @@
 cabal-version:      2.4
 name:               dataframe
-version:            0.3.5.0
+version:            0.4.0.0
 
 synopsis: A fast, safe, and intuitive DataFrame library.
 
@@ -107,6 +107,7 @@
                       unordered-containers >= 0.1 && < 1,
                       vector ^>= 0.13,
                       vector-algorithms ^>= 0.9,
+                      zlib >= 0.5 && < 1,
                       zstd >= 0.1.2.0 && < 0.2,
                       mmap >= 0.5.8 && <= 0.5.9,
                       parallel >= 3.2.2.0 && < 5
@@ -121,7 +122,7 @@
     import: warnings
     main-is: Benchmark.hs
     build-depends:    base >= 4 && < 5,
-                      dataframe ^>= 0.3,
+                      dataframe ^>= 0.4,
                       random >= 1 && < 2,
                       time >= 1.12 && < 2,
                       vector ^>= 0.13,
@@ -150,7 +151,7 @@
     build-depends: base >= 4 && < 5,
                    criterion >= 1 && < 2,
                    process >= 1.6 && < 2,
-                   dataframe ^>= 0.3
+                   dataframe ^>= 0.4
     default-language: Haskell2010
     ghc-options:
       -threaded
@@ -178,7 +179,7 @@
                    Operations.Take,
                    Parquet
     build-depends:  base >= 4 && < 5,
-                    dataframe ^>= 0.3,
+                    dataframe ^>= 0.4,
                     HUnit ^>= 1.6,
                     random >= 1 && < 2,
                     random-shuffle >= 0.0.4 && < 1,
diff --git a/src/DataFrame.hs b/src/DataFrame.hs
--- a/src/DataFrame.hs
+++ b/src/DataFrame.hs
@@ -270,16 +270,8 @@
 import DataFrame.Internal.DataFrame as Dataframe (
     DataFrame,
     GroupedDataFrame,
-    columnAsDoubleVector,
-    columnAsFloatVector,
-    columnAsIntVector,
-    columnAsList,
-    columnAsVector,
     empty,
     null,
-    toDoubleMatrix,
-    toFloatMatrix,
-    toIntMatrix,
     toMarkdownTable,
  )
 import DataFrame.Internal.Expression as Expression (Expr)
@@ -317,6 +309,7 @@
     imputeWith,
     interQuartileRange,
     mean,
+    meanMaybe,
     median,
     skewness,
     standardDeviation,
diff --git a/src/DataFrame/Functions.hs b/src/DataFrame/Functions.hs
--- a/src/DataFrame/Functions.hs
+++ b/src/DataFrame/Functions.hs
@@ -39,6 +39,7 @@
 import qualified Data.Vector as V
 import qualified Data.Vector.Unboxed as VU
 import qualified DataFrame.IO.CSV as CSV
+import qualified DataFrame.IO.Parquet as Parquet
 import Debug.Trace (trace)
 import Language.Haskell.TH
 import qualified Language.Haskell.TH.Syntax as TH
@@ -46,7 +47,7 @@
 import Prelude hiding (maximum, minimum)
 import Prelude as P
 
-infix 4 .==, .<, .<=, .>=, .>
+infix 4 .==, .<, .<=, .>=, .>, ./=
 infixr 3 .&&
 infixr 2 .||
 
@@ -92,6 +93,9 @@
 (.==) :: (Columnable a, Eq a) => Expr a -> Expr a -> Expr Bool
 (.==) = BinaryOp "eq" (==)
 
+(./=) :: (Columnable a, Eq a) => Expr a -> Expr a -> Expr Bool
+(./=) = BinaryOp "eq" (/=)
+
 eq :: (Columnable a, Eq a) => Expr a -> Expr a -> Expr Bool
 eq = BinaryOp "eq" (==)
 
@@ -101,11 +105,15 @@
 lt :: (Columnable a, Ord a) => Expr a -> Expr a -> Expr Bool
 lt = BinaryOp "lt" (<)
 
+-- TODO: Generalize this pattern for other equality functions.
 (.>) :: (Columnable a, Ord a) => Expr a -> Expr a -> Expr Bool
-(.>) = BinaryOp "gt" (>)
+(.>) (Lit l) (Lit r) = Lit (l > r)
+(.>) (Lit l) expr = UnaryOp ("gt " <> T.pack (show l)) (l >) expr
+(.>) expr (Lit r) = UnaryOp ("leq " <> T.pack (show r)) (r <=) expr
+(.>) l r = BinaryOp "gt" (>) l r
 
 gt :: (Columnable a, Ord a) => Expr a -> Expr a -> Expr Bool
-gt = BinaryOp "gt" (>)
+gt = (.>)
 
 (.<=) :: (Columnable a, Ord a, Eq a) => Expr a -> Expr a -> Expr Bool
 (.<=) = BinaryOp "leq" (<=)
@@ -203,6 +211,7 @@
 
 pow :: (Columnable a, Num a) => Expr a -> Int -> Expr a
 pow _ 0 = Lit 1
+pow (Lit n) i = Lit (n ^ i)
 pow expr 1 = expr
 pow expr i = UnaryOp ("pow " <> T.pack (show i)) (^ i) expr
 
@@ -363,6 +372,17 @@
 declareColumnsFromCsvFile :: String -> DecsQ
 declareColumnsFromCsvFile path = do
     df <- liftIO (CSV.readCsv path)
+    declareColumns df
+
+-- TODO: We don't have to read the whole file, we can just read the schema.
+declareColumnsFromParquetFile :: String -> DecsQ
+declareColumnsFromParquetFile path = do
+    df <- liftIO (Parquet.readParquet path)
+    declareColumns df
+
+declareColumnsFromCsvWithOpts :: CSV.ReadOptions -> String -> DecsQ
+declareColumnsFromCsvWithOpts opts path = do
+    df <- liftIO (CSV.readSeparated opts path)
     declareColumns df
 
 declareColumns :: DataFrame -> DecsQ
diff --git a/src/DataFrame/IO/CSV.hs b/src/DataFrame/IO/CSV.hs
--- a/src/DataFrame/IO/CSV.hs
+++ b/src/DataFrame/IO/CSV.hs
@@ -163,6 +163,8 @@
     Just 2010-03-04
     @
     -}
+    , columnSeparator :: Char
+    -- ^ Character that separates column values.
     }
 
 shouldInferFromSample :: TypeSpec -> Bool
@@ -184,6 +186,7 @@
         , typeSpec = InferFromSample 100
         , safeRead = True
         , dateFormat = "%Y-%m-%d"
+        , columnSeparator = ','
         }
 
 {- | Read CSV file from path and load it into a dataframe.
@@ -195,7 +198,7 @@
 @
 -}
 readCsv :: FilePath -> IO DataFrame
-readCsv = readSeparated ',' defaultReadOptions
+readCsv = readSeparated defaultReadOptions
 
 {- | Read CSV file from path and load it into a dataframe.
 
@@ -206,7 +209,7 @@
 @
 -}
 readCsvWithOpts :: ReadOptions -> FilePath -> IO DataFrame
-readCsvWithOpts = readSeparated ','
+readCsvWithOpts = readSeparated
 
 {- | Read TSV (tab separated) file from path and load it into a dataframe.
 
@@ -217,18 +220,19 @@
 @
 -}
 readTsv :: FilePath -> IO DataFrame
-readTsv = readSeparated '\t' defaultReadOptions
+readTsv = readSeparated (defaultReadOptions{columnSeparator = '\t'})
 
 {- | Read text file with specified delimiter into a dataframe.
 
 ==== __Example__
 @
-ghci> D.readSeparated ';' D.defaultReadOptions ".\/data\/taxi.txt"
+ghci> D.readSeparated (D.defaultReadOptions { columnSeparator = ';' }) ".\/data\/taxi.txt"
 
 @
 -}
-readSeparated :: Char -> ReadOptions -> FilePath -> IO DataFrame
-readSeparated !sep !opts !path = do
+readSeparated :: ReadOptions -> FilePath -> IO DataFrame
+readSeparated !opts !path = do
+    let sep = columnSeparator opts
     csvData <- BL.readFile path
     let decodeOpts = Csv.defaultDecodeOptions{Csv.decDelimiter = fromIntegral (ord sep)}
     let stream = CsvStream.decodeWith decodeOpts Csv.NoHeader csvData
diff --git a/src/DataFrame/IO/Parquet/Page.hs b/src/DataFrame/IO/Parquet/Page.hs
--- a/src/DataFrame/IO/Parquet/Page.hs
+++ b/src/DataFrame/IO/Parquet/Page.hs
@@ -3,9 +3,11 @@
 
 module DataFrame.IO.Parquet.Page where
 
+import qualified Codec.Compression.GZip as GZip
 import Codec.Compression.Zstd.Streaming
 import Data.Bits
 import qualified Data.ByteString as BSO
+import qualified Data.ByteString.Lazy as LB
 import Data.Int
 import Data.Maybe (fromMaybe, listToMaybe)
 import Data.Word
@@ -42,6 +44,7 @@
             Left e -> error (show e)
             Right res -> pure res
         UNCOMPRESSED -> pure (BSO.pack compressed)
+        GZIP -> pure (LB.toStrict (GZip.decompress (LB.pack compressed)))
         other -> error ("Unsupported compression type: " ++ show other)
     pure
         ( Just $ Page hdr (BSO.unpack fullData)
diff --git a/src/DataFrame/IO/Parquet/Thrift.hs b/src/DataFrame/IO/Parquet/Thrift.hs
--- a/src/DataFrame/IO/Parquet/Thrift.hs
+++ b/src/DataFrame/IO/Parquet/Thrift.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE StrictData #-}
 {-# LANGUAGE TypeApplications #-}
 
 module DataFrame.IO.Parquet.Thrift where
@@ -202,8 +203,8 @@
                 ]
 
 readField ::
-    BS.ByteString -> IORef Int -> Int16 -> [Int16] -> IO (Maybe (TType, Int16))
-readField buf pos lastFieldId fieldStack = do
+    BS.ByteString -> IORef Int -> Int16 -> IO (Maybe (TType, Int16))
+readField buf pos lastFieldId = do
     t <- readAndAdvance pos buf
     if t .&. 0x0f == 0
         then return Nothing
@@ -256,19 +257,17 @@
             BS.pack $
                 map (BS.index contents) [metadataStartPos .. (metadataStartPos + size - 1)]
     let lastFieldId = 0
-    let fieldStack = []
     bufferPos <- newIORef (0 :: Int)
-    readFileMetaData defaultMetadata metadataBytes bufferPos lastFieldId fieldStack
+    readFileMetaData defaultMetadata metadataBytes bufferPos lastFieldId
 
 readFileMetaData ::
     FileMetadata ->
     BS.ByteString ->
     IORef Int ->
     Int16 ->
-    [Int16] ->
     IO FileMetadata
-readFileMetaData metadata metaDataBuf bufferPos lastFieldId fieldStack = do
-    fieldContents <- readField metaDataBuf bufferPos lastFieldId fieldStack
+readFileMetaData metadata metaDataBuf bufferPos lastFieldId = do
+    fieldContents <- readField metaDataBuf bufferPos lastFieldId
     case fieldContents of
         Nothing -> return metadata
         Just (elemType, identifier) -> case identifier of
@@ -279,7 +278,6 @@
                     metaDataBuf
                     bufferPos
                     identifier
-                    fieldStack
             2 -> do
                 sizeAndType <- readAndAdvance bufferPos metaDataBuf
                 listSize <-
@@ -290,13 +288,12 @@
                 schemaElements <-
                     replicateM
                         listSize
-                        (readSchemaElement defaultSchemaElement metaDataBuf bufferPos 0 [])
+                        (readSchemaElement defaultSchemaElement metaDataBuf bufferPos 0)
                 readFileMetaData
                     (metadata{schema = schemaElements})
                     metaDataBuf
                     bufferPos
                     identifier
-                    fieldStack
             3 -> do
                 numRows <- readIntFromBuffer @Int64 metaDataBuf bufferPos
                 readFileMetaData
@@ -304,7 +301,6 @@
                     metaDataBuf
                     bufferPos
                     identifier
-                    fieldStack
             4 -> do
                 sizeAndType <- readAndAdvance bufferPos metaDataBuf
                 listSize <-
@@ -315,13 +311,12 @@
                 -- TODO actually check elemType agrees (also for all the other underscored _elemType in this module)
                 let _elemType = toTType sizeAndType
                 rowGroups <-
-                    replicateM listSize (readRowGroup emptyRowGroup metaDataBuf bufferPos 0 [])
+                    replicateM listSize (readRowGroup emptyRowGroup metaDataBuf bufferPos 0)
                 readFileMetaData
                     (metadata{rowGroups = rowGroups})
                     metaDataBuf
                     bufferPos
                     identifier
-                    fieldStack
             5 -> do
                 sizeAndType <- readAndAdvance bufferPos metaDataBuf
                 listSize <-
@@ -331,13 +326,12 @@
 
                 let _elemType = toTType sizeAndType
                 keyValueMetadata <-
-                    replicateM listSize (readKeyValue emptyKeyValue metaDataBuf bufferPos 0 [])
+                    replicateM listSize (readKeyValue emptyKeyValue metaDataBuf bufferPos 0)
                 readFileMetaData
                     (metadata{keyValueMetadata = keyValueMetadata})
                     metaDataBuf
                     bufferPos
                     identifier
-                    fieldStack
             6 -> do
                 createdBy <- readString metaDataBuf bufferPos
                 readFileMetaData
@@ -345,7 +339,6 @@
                     metaDataBuf
                     bufferPos
                     identifier
-                    fieldStack
             7 -> do
                 sizeAndType <- readAndAdvance bufferPos metaDataBuf
                 listSize <-
@@ -354,21 +347,19 @@
                         else return $ fromIntegral ((sizeAndType `shiftR` 4) .&. 0x0f)
 
                 let _elemType = toTType sizeAndType
-                columnOrders <- replicateM listSize (readColumnOrder metaDataBuf bufferPos 0 [])
+                columnOrders <- replicateM listSize (readColumnOrder metaDataBuf bufferPos 0)
                 readFileMetaData
                     (metadata{columnOrders = columnOrders})
                     metaDataBuf
                     bufferPos
                     identifier
-                    fieldStack
             8 -> do
-                encryptionAlgorithm <- readEncryptionAlgorithm metaDataBuf bufferPos 0 []
+                encryptionAlgorithm <- readEncryptionAlgorithm metaDataBuf bufferPos 0
                 readFileMetaData
                     (metadata{encryptionAlgorithm = encryptionAlgorithm})
                     metaDataBuf
                     bufferPos
                     identifier
-                    fieldStack
             9 -> do
                 footerSigningKeyMetadata <- readByteString metaDataBuf bufferPos
                 readFileMetaData
@@ -376,7 +367,6 @@
                     metaDataBuf
                     bufferPos
                     identifier
-                    fieldStack
             n -> return $ error $ "UNIMPLEMENTED " ++ show n
 
 readSchemaElement ::
@@ -384,13 +374,11 @@
     BS.ByteString ->
     IORef Int ->
     Int16 ->
-    [Int16] ->
     IO SchemaElement
-readSchemaElement schemaElement buf pos lastFieldId fieldStack = do
-    fieldContents <- readField buf pos lastFieldId fieldStack
+readSchemaElement schemaElement buf pos lastFieldId = do
+    fieldContents <- readField buf pos lastFieldId
     case fieldContents of
         Nothing -> return schemaElement
-        Just (STOP, _) -> return schemaElement
         Just (elemType, identifier) -> case identifier of
             1 -> do
                 schemaElemType <- toIntegralType <$> readInt32FromBuffer buf pos
@@ -399,7 +387,6 @@
                     buf
                     pos
                     identifier
-                    fieldStack
             2 -> do
                 typeLength <- readInt32FromBuffer buf pos
                 readSchemaElement
@@ -407,7 +394,6 @@
                     buf
                     pos
                     identifier
-                    fieldStack
             3 -> do
                 fieldRepetitionType <- readInt32FromBuffer buf pos
                 readSchemaElement
@@ -415,11 +401,10 @@
                     buf
                     pos
                     identifier
-                    fieldStack
             4 -> do
                 nameSize <- readVarIntFromBuffer @Int buf pos
                 if nameSize <= 0
-                    then readSchemaElement schemaElement buf pos identifier fieldStack
+                    then readSchemaElement schemaElement buf pos identifier
                     else do
                         contents <- replicateM nameSize (readAndAdvance pos buf)
                         readSchemaElement
@@ -427,7 +412,6 @@
                             buf
                             pos
                             identifier
-                            fieldStack
             5 -> do
                 numChildren <- readInt32FromBuffer buf pos
                 readSchemaElement
@@ -435,7 +419,6 @@
                     buf
                     pos
                     identifier
-                    fieldStack
             6 -> do
                 convertedType <- readInt32FromBuffer buf pos
                 readSchemaElement
@@ -443,10 +426,9 @@
                     buf
                     pos
                     identifier
-                    fieldStack
             7 -> do
                 scale <- readInt32FromBuffer buf pos
-                readSchemaElement (schemaElement{scale = scale}) buf pos identifier fieldStack
+                readSchemaElement (schemaElement{scale = scale}) buf pos identifier
             8 -> do
                 precision <- readInt32FromBuffer buf pos
                 readSchemaElement
@@ -454,7 +436,6 @@
                     buf
                     pos
                     identifier
-                    fieldStack
             9 -> do
                 fieldId <- readInt32FromBuffer buf pos
                 readSchemaElement
@@ -462,21 +443,19 @@
                     buf
                     pos
                     identifier
-                    fieldStack
             10 -> do
-                logicalType <- readLogicalType buf pos 0 []
+                logicalType <- readLogicalType LOGICAL_TYPE_UNKNOWN buf pos 0
                 readSchemaElement
                     (schemaElement{logicalType = logicalType})
                     buf
                     pos
                     identifier
-                    fieldStack
-            _ -> error "Uknown schema element"
+            n -> error ("Uknown schema element: " ++ show n)
 
 readRowGroup ::
-    RowGroup -> BS.ByteString -> IORef Int -> Int16 -> [Int16] -> IO RowGroup
-readRowGroup r buf pos lastFieldId fieldStack = do
-    fieldContents <- readField buf pos lastFieldId fieldStack
+    RowGroup -> BS.ByteString -> IORef Int -> Int16 -> IO RowGroup
+readRowGroup r buf pos lastFieldId = do
+    fieldContents <- readField buf pos lastFieldId
     case fieldContents of
         Nothing -> return r
         Just (elemType, identifier) -> case identifier of
@@ -488,18 +467,18 @@
                         else return $ fromIntegral ((sizeAndType `shiftR` 4) .&. 0x0f)
                 let _elemType = toTType sizeAndType
                 columnChunks <-
-                    replicateM listSize (readColumnChunk emptyColumnChunk buf pos 0 [])
-                readRowGroup (r{rowGroupColumns = columnChunks}) buf pos identifier fieldStack
+                    replicateM listSize (readColumnChunk emptyColumnChunk buf pos 0)
+                readRowGroup (r{rowGroupColumns = columnChunks}) buf pos identifier
             2 -> do
                 totalBytes <- readIntFromBuffer @Int64 buf pos
-                readRowGroup (r{totalByteSize = totalBytes}) buf pos identifier fieldStack
+                readRowGroup (r{totalByteSize = totalBytes}) buf pos identifier
             3 -> do
                 nRows <- readIntFromBuffer @Int64 buf pos
-                readRowGroup (r{rowGroupNumRows = nRows}) buf pos identifier fieldStack
+                readRowGroup (r{rowGroupNumRows = nRows}) buf pos identifier
             4 -> return r
             5 -> do
                 offset <- readIntFromBuffer @Int64 buf pos
-                readRowGroup (r{fileOffset = offset}) buf pos identifier fieldStack
+                readRowGroup (r{fileOffset = offset}) buf pos identifier
             6 -> do
                 compressedSize <- readIntFromBuffer @Int64 buf pos
                 readRowGroup
@@ -507,16 +486,15 @@
                     buf
                     pos
                     identifier
-                    fieldStack
             7 -> do
                 ordinal <- readIntFromBuffer @Int16 buf pos
-                readRowGroup (r{ordinal = ordinal}) buf pos identifier fieldStack
+                readRowGroup (r{ordinal = ordinal}) buf pos identifier
             _ -> error $ "Unknown row group field: " ++ show identifier
 
 readColumnChunk ::
-    ColumnChunk -> BS.ByteString -> IORef Int -> Int16 -> [Int16] -> IO ColumnChunk
-readColumnChunk c buf pos lastFieldId fieldStack = do
-    fieldContents <- readField buf pos lastFieldId fieldStack
+    ColumnChunk -> BS.ByteString -> IORef Int -> Int16 -> IO ColumnChunk
+readColumnChunk c buf pos lastFieldId = do
+    fieldContents <- readField buf pos lastFieldId
     case fieldContents of
         Nothing -> return c
         Just (elemType, identifier) -> case identifier of
@@ -529,7 +507,6 @@
                     buf
                     pos
                     identifier
-                    fieldStack
             2 -> do
                 columnChunkMetadataFileOffset <- readIntFromBuffer @Int64 buf pos
                 readColumnChunk
@@ -537,15 +514,13 @@
                     buf
                     pos
                     identifier
-                    fieldStack
             3 -> do
-                columnMetadata <- readColumnMetadata emptyColumnMetadata buf pos 0 []
+                columnMetadata <- readColumnMetadata emptyColumnMetadata buf pos 0
                 readColumnChunk
                     (c{columnMetaData = columnMetadata})
                     buf
                     pos
                     identifier
-                    fieldStack
             4 -> do
                 columnOffsetIndexOffset <- readIntFromBuffer @Int64 buf pos
                 readColumnChunk
@@ -553,7 +528,6 @@
                     buf
                     pos
                     identifier
-                    fieldStack
             5 -> do
                 columnOffsetIndexLength <- readInt32FromBuffer buf pos
                 readColumnChunk
@@ -561,7 +535,6 @@
                     buf
                     pos
                     identifier
-                    fieldStack
             6 -> do
                 columnChunkColumnIndexOffset <- readIntFromBuffer @Int64 buf pos
                 readColumnChunk
@@ -569,7 +542,6 @@
                     buf
                     pos
                     identifier
-                    fieldStack
             7 -> do
                 columnChunkColumnIndexLength <- readInt32FromBuffer buf pos
                 readColumnChunk
@@ -577,7 +549,6 @@
                     buf
                     pos
                     identifier
-                    fieldStack
             _ -> error "Unknown column chunk"
 
 readColumnMetadata ::
@@ -585,27 +556,25 @@
     BS.ByteString ->
     IORef Int ->
     Int16 ->
-    [Int16] ->
     IO ColumnMetaData
-readColumnMetadata cm buf pos lastFieldId fieldStack = do
-    fieldContents <- readField buf pos lastFieldId fieldStack
+readColumnMetadata cm buf pos lastFieldId = do
+    fieldContents <- readField buf pos lastFieldId
     case fieldContents of
         Nothing -> return cm
         Just (elemType, identifier) -> case identifier of
             1 -> do
                 cType <- parquetTypeFromInt <$> readInt32FromBuffer buf pos
-                readColumnMetadata (cm{columnType = cType}) buf pos identifier []
+                readColumnMetadata (cm{columnType = cType}) buf pos identifier
             2 -> do
                 sizeAndType <- readAndAdvance pos buf
                 let sizeOnly = fromIntegral ((sizeAndType `shiftR` 4) .&. 0x0f) :: Int
                 let _elemType = toTType sizeAndType
-                encodings <- replicateM sizeOnly (readParquetEncoding buf pos 0 [])
+                encodings <- replicateM sizeOnly (readParquetEncoding buf pos 0)
                 readColumnMetadata
                     (cm{columnEncodings = encodings})
                     buf
                     pos
                     identifier
-                    fieldStack
             3 -> do
                 sizeAndType <- readAndAdvance pos buf
                 let sizeOnly = fromIntegral ((sizeAndType `shiftR` 4) .&. 0x0f) :: Int
@@ -616,13 +585,12 @@
                     buf
                     pos
                     identifier
-                    fieldStack
             4 -> do
                 cType <- compressionCodecFromInt <$> readInt32FromBuffer buf pos
-                readColumnMetadata (cm{columnCodec = cType}) buf pos identifier []
+                readColumnMetadata (cm{columnCodec = cType}) buf pos identifier
             5 -> do
                 numValues <- readIntFromBuffer @Int64 buf pos
-                readColumnMetadata (cm{columnNumValues = numValues}) buf pos identifier []
+                readColumnMetadata (cm{columnNumValues = numValues}) buf pos identifier
             6 -> do
                 columnTotalUncompressedSize <- readIntFromBuffer @Int64 buf pos
                 readColumnMetadata
@@ -630,7 +598,6 @@
                     buf
                     pos
                     identifier
-                    []
             7 -> do
                 columnTotalCompressedSize <- readIntFromBuffer @Int64 buf pos
                 readColumnMetadata
@@ -638,19 +605,17 @@
                     buf
                     pos
                     identifier
-                    []
             8 -> do
                 sizeAndType <- readAndAdvance pos buf
                 let sizeOnly = fromIntegral ((sizeAndType `shiftR` 4) .&. 0x0f) :: Int
                 let _elemType = toTType sizeAndType
                 columnKeyValueMetadata <-
-                    replicateM sizeOnly (readKeyValue emptyKeyValue buf pos 0 [])
+                    replicateM sizeOnly (readKeyValue emptyKeyValue buf pos 0)
                 readColumnMetadata
                     (cm{columnKeyValueMetadata = columnKeyValueMetadata})
                     buf
                     pos
                     identifier
-                    fieldStack
             9 -> do
                 columnDataPageOffset <- readIntFromBuffer @Int64 buf pos
                 readColumnMetadata
@@ -658,7 +623,6 @@
                     buf
                     pos
                     identifier
-                    []
             10 -> do
                 columnIndexPageOffset <- readIntFromBuffer @Int64 buf pos
                 readColumnMetadata
@@ -666,7 +630,6 @@
                     buf
                     pos
                     identifier
-                    []
             11 -> do
                 columnDictionaryPageOffset <- readIntFromBuffer @Int64 buf pos
                 readColumnMetadata
@@ -674,22 +637,20 @@
                     buf
                     pos
                     identifier
-                    []
             12 -> do
-                stats <- readStatistics emptyColumnStatistics buf pos 0 []
-                readColumnMetadata (cm{columnStatistics = stats}) buf pos identifier fieldStack
+                stats <- readStatistics emptyColumnStatistics buf pos 0
+                readColumnMetadata (cm{columnStatistics = stats}) buf pos identifier
             13 -> do
                 sizeAndType <- readAndAdvance pos buf
                 let sizeOnly = fromIntegral ((sizeAndType `shiftR` 4) .&. 0x0f) :: Int
                 let _elemType = toTType sizeAndType
                 pageEncodingStats <-
-                    replicateM sizeOnly (readPageEncodingStats emptyPageEncodingStats buf pos 0 [])
+                    replicateM sizeOnly (readPageEncodingStats emptyPageEncodingStats buf pos 0)
                 readColumnMetadata
                     (cm{columnEncodingStats = pageEncodingStats})
                     buf
                     pos
                     identifier
-                    fieldStack
             14 -> do
                 bloomFilterOffset <- readIntFromBuffer @Int64 buf pos
                 readColumnMetadata
@@ -697,7 +658,6 @@
                     buf
                     pos
                     identifier
-                    []
             15 -> do
                 bloomFilterLength <- readInt32FromBuffer buf pos
                 readColumnMetadata
@@ -705,22 +665,20 @@
                     buf
                     pos
                     identifier
-                    []
             16 -> do
-                stats <- readSizeStatistics emptySizeStatistics buf pos 0 []
+                stats <- readSizeStatistics emptySizeStatistics buf pos 0
                 readColumnMetadata
                     (cm{columnSizeStatistics = stats})
                     buf
                     pos
                     identifier
-                    fieldStack
             17 -> return $ error "UNIMPLEMENTED"
             _ -> error $ "Unknown column metadata " ++ show identifier
 
 readEncryptionAlgorithm ::
-    BS.ByteString -> IORef Int -> Int16 -> [Int16] -> IO EncryptionAlgorithm
-readEncryptionAlgorithm buf pos lastFieldId fieldStack = do
-    fieldContents <- readField buf pos lastFieldId fieldStack
+    BS.ByteString -> IORef Int -> Int16 -> IO EncryptionAlgorithm
+readEncryptionAlgorithm buf pos lastFieldId = do
+    fieldContents <- readField buf pos lastFieldId
     case fieldContents of
         Nothing -> return ENCRYPTION_ALGORITHM_UNKNOWN
         Just (elemType, identifier) -> case identifier of
@@ -730,25 +688,24 @@
                     buf
                     pos
                     0
-                    []
             2 -> do
                 readAesGcmCtrV1
                     (AesGcmCtrV1{aadPrefix = [], aadFileUnique = [], supplyAadPrefix = False})
                     buf
                     pos
                     0
-                    []
             n -> return ENCRYPTION_ALGORITHM_UNKNOWN
 
 readColumnOrder ::
-    BS.ByteString -> IORef Int -> Int16 -> [Int16] -> IO ColumnOrder
-readColumnOrder buf pos lastFieldId fieldStack = do
-    fieldContents <- readField buf pos lastFieldId fieldStack
+    BS.ByteString -> IORef Int -> Int16 -> IO ColumnOrder
+readColumnOrder buf pos lastFieldId = do
+    fieldContents <- readField buf pos lastFieldId
     case fieldContents of
         Nothing -> return COLUMN_ORDER_UNKNOWN
         Just (elemType, identifier) -> case identifier of
             1 -> do
-                replicateM_ 2 (readTypeOrder buf pos 0 [])
+                -- Read begin struct and stop since this an empty struct.
+                replicateM_ 2 (readTypeOrder buf pos 0)
                 return TYPE_ORDER
             _ -> return COLUMN_ORDER_UNKNOWN
 
@@ -757,16 +714,15 @@
     BS.ByteString ->
     IORef Int ->
     Int16 ->
-    [Int16] ->
     IO EncryptionAlgorithm
-readAesGcmCtrV1 v@(AesGcmCtrV1 aadPrefix aadFileUnique supplyAadPrefix) buf pos lastFieldId fieldStack = do
-    fieldContents <- readField buf pos lastFieldId fieldStack
+readAesGcmCtrV1 v@(AesGcmCtrV1 aadPrefix aadFileUnique supplyAadPrefix) buf pos lastFieldId = do
+    fieldContents <- readField buf pos lastFieldId
     case fieldContents of
         Nothing -> return v
         Just (elemType, identifier) -> case identifier of
             1 -> do
                 aadPrefix <- readByteString buf pos
-                readAesGcmCtrV1 (v{aadPrefix = aadPrefix}) buf pos lastFieldId fieldStack
+                readAesGcmCtrV1 (v{aadPrefix = aadPrefix}) buf pos lastFieldId
             2 -> do
                 aadFileUnique <- readByteString buf pos
                 readAesGcmCtrV1
@@ -774,7 +730,6 @@
                     buf
                     pos
                     lastFieldId
-                    fieldStack
             3 -> do
                 supplyAadPrefix <- readAndAdvance pos buf
                 readAesGcmCtrV1
@@ -782,9 +737,8 @@
                     buf
                     pos
                     lastFieldId
-                    fieldStack
             _ -> return ENCRYPTION_ALGORITHM_UNKNOWN
-readAesGcmCtrV1 _ _ _ _ _ =
+readAesGcmCtrV1 _ _ _ _ =
     error "readAesGcmCtrV1 called with non AesGcmCtrV1"
 
 readAesGcmV1 ::
@@ -792,19 +746,18 @@
     BS.ByteString ->
     IORef Int ->
     Int16 ->
-    [Int16] ->
     IO EncryptionAlgorithm
-readAesGcmV1 v@(AesGcmV1 aadPrefix aadFileUnique supplyAadPrefix) buf pos lastFieldId fieldStack = do
-    fieldContents <- readField buf pos lastFieldId fieldStack
+readAesGcmV1 v@(AesGcmV1 aadPrefix aadFileUnique supplyAadPrefix) buf pos lastFieldId = do
+    fieldContents <- readField buf pos lastFieldId
     case fieldContents of
         Nothing -> return v
         Just (elemType, identifier) -> case identifier of
             1 -> do
                 aadPrefix <- readByteString buf pos
-                readAesGcmV1 (v{aadPrefix = aadPrefix}) buf pos lastFieldId fieldStack
+                readAesGcmV1 (v{aadPrefix = aadPrefix}) buf pos lastFieldId
             2 -> do
                 aadFileUnique <- readByteString buf pos
-                readAesGcmV1 (v{aadFileUnique = aadFileUnique}) buf pos lastFieldId fieldStack
+                readAesGcmV1 (v{aadFileUnique = aadFileUnique}) buf pos lastFieldId
             3 -> do
                 supplyAadPrefix <- readAndAdvance pos buf
                 readAesGcmV1
@@ -812,35 +765,34 @@
                     buf
                     pos
                     lastFieldId
-                    fieldStack
             _ -> return ENCRYPTION_ALGORITHM_UNKNOWN
-readAesGcmV1 _ _ _ _ _ =
+readAesGcmV1 _ _ _ _ =
     error "readAesGcmV1 called with non AesGcmV1"
 
 readTypeOrder ::
-    BS.ByteString -> IORef Int -> Int16 -> [Int16] -> IO ColumnOrder
-readTypeOrder buf pos lastFieldId fieldStack = do
-    fieldContents <- readField buf pos lastFieldId fieldStack
+    BS.ByteString -> IORef Int -> Int16 -> IO ColumnOrder
+readTypeOrder buf pos lastFieldId = do
+    fieldContents <- readField buf pos lastFieldId
     case fieldContents of
         Nothing -> return TYPE_ORDER
         Just (elemType, identifier) ->
             if elemType == STOP
                 then return TYPE_ORDER
-                else readTypeOrder buf pos identifier fieldStack
+                else readTypeOrder buf pos identifier
 
 readKeyValue ::
-    KeyValue -> BS.ByteString -> IORef Int -> Int16 -> [Int16] -> IO KeyValue
-readKeyValue kv buf pos lastFieldId fieldStack = do
-    fieldContents <- readField buf pos lastFieldId fieldStack
+    KeyValue -> BS.ByteString -> IORef Int -> Int16 -> IO KeyValue
+readKeyValue kv buf pos lastFieldId = do
+    fieldContents <- readField buf pos lastFieldId
     case fieldContents of
         Nothing -> return kv
         Just (elemType, identifier) -> case identifier of
             1 -> do
                 k <- readString buf pos
-                readKeyValue (kv{key = k}) buf pos identifier fieldStack
+                readKeyValue (kv{key = k}) buf pos identifier
             2 -> do
                 v <- readString buf pos
-                readKeyValue (kv{value = v}) buf pos identifier fieldStack
+                readKeyValue (kv{value = v}) buf pos identifier
             _ -> error "Unknown kv"
 
 readPageEncodingStats ::
@@ -848,19 +800,18 @@
     BS.ByteString ->
     IORef Int ->
     Int16 ->
-    [Int16] ->
     IO PageEncodingStats
-readPageEncodingStats pes buf pos lastFieldId fieldStack = do
-    fieldContents <- readField buf pos lastFieldId fieldStack
+readPageEncodingStats pes buf pos lastFieldId = do
+    fieldContents <- readField buf pos lastFieldId
     case fieldContents of
         Nothing -> return pes
         Just (elemType, identifier) -> case identifier of
             1 -> do
                 pType <- pageTypeFromInt <$> readInt32FromBuffer buf pos
-                readPageEncodingStats (pes{pageEncodingPageType = pType}) buf pos identifier []
+                readPageEncodingStats (pes{pageEncodingPageType = pType}) buf pos identifier
             2 -> do
                 pEnc <- parquetEncodingFromInt <$> readInt32FromBuffer buf pos
-                readPageEncodingStats (pes{pageEncoding = pEnc}) buf pos identifier []
+                readPageEncodingStats (pes{pageEncoding = pEnc}) buf pos identifier
             3 -> do
                 encodedCount <- readInt32FromBuffer buf pos
                 readPageEncodingStats
@@ -868,34 +819,32 @@
                     buf
                     pos
                     identifier
-                    []
             _ -> error "Unknown page encoding stats"
 
 readParquetEncoding ::
-    BS.ByteString -> IORef Int -> Int16 -> [Int16] -> IO ParquetEncoding
-readParquetEncoding buf pos lastFieldId fieldStack = parquetEncodingFromInt <$> readInt32FromBuffer buf pos
+    BS.ByteString -> IORef Int -> Int16 -> IO ParquetEncoding
+readParquetEncoding buf pos lastFieldId = parquetEncodingFromInt <$> readInt32FromBuffer buf pos
 
 readStatistics ::
     ColumnStatistics ->
     BS.ByteString ->
     IORef Int ->
     Int16 ->
-    [Int16] ->
     IO ColumnStatistics
-readStatistics cs buf pos lastFieldId fieldStack = do
-    fieldContents <- readField buf pos lastFieldId fieldStack
+readStatistics cs buf pos lastFieldId = do
+    fieldContents <- readField buf pos lastFieldId
     case fieldContents of
         Nothing -> return cs
         Just (elemType, identifier) -> case identifier of
             1 -> do
                 maxInBytes <- readByteString buf pos
-                readStatistics (cs{columnMax = maxInBytes}) buf pos identifier fieldStack
+                readStatistics (cs{columnMax = maxInBytes}) buf pos identifier
             2 -> do
                 minInBytes <- readByteString buf pos
-                readStatistics (cs{columnMin = minInBytes}) buf pos identifier fieldStack
+                readStatistics (cs{columnMin = minInBytes}) buf pos identifier
             3 -> do
                 nullCount <- readIntFromBuffer @Int64 buf pos
-                readStatistics (cs{columnNullCount = nullCount}) buf pos identifier fieldStack
+                readStatistics (cs{columnNullCount = nullCount}) buf pos identifier
             4 -> do
                 distinctCount <- readIntFromBuffer @Int64 buf pos
                 readStatistics
@@ -903,13 +852,12 @@
                     buf
                     pos
                     identifier
-                    fieldStack
             5 -> do
                 maxInBytes <- readByteString buf pos
-                readStatistics (cs{columnMaxValue = maxInBytes}) buf pos identifier fieldStack
+                readStatistics (cs{columnMaxValue = maxInBytes}) buf pos identifier
             6 -> do
                 minInBytes <- readByteString buf pos
-                readStatistics (cs{columnMinValue = minInBytes}) buf pos identifier fieldStack
+                readStatistics (cs{columnMinValue = minInBytes}) buf pos identifier
             7 -> do
                 isMaxValueExact <- readAndAdvance pos buf
                 readStatistics
@@ -917,7 +865,6 @@
                     buf
                     pos
                     identifier
-                    fieldStack
             8 -> do
                 isMinValueExact <- readAndAdvance pos buf
                 readStatistics
@@ -925,7 +872,6 @@
                     buf
                     pos
                     identifier
-                    fieldStack
             _ -> error "Unknown statistics"
 
 readSizeStatistics ::
@@ -933,10 +879,9 @@
     BS.ByteString ->
     IORef Int ->
     Int16 ->
-    [Int16] ->
     IO SizeStatistics
-readSizeStatistics ss buf pos lastFieldId fieldStack = do
-    fieldContents <- readField buf pos lastFieldId fieldStack
+readSizeStatistics ss buf pos lastFieldId = do
+    fieldContents <- readField buf pos lastFieldId
     case fieldContents of
         Nothing -> return ss
         Just (elemType, identifier) -> case identifier of
@@ -947,7 +892,6 @@
                     buf
                     pos
                     identifier
-                    fieldStack
             2 -> do
                 sizeAndType <- readAndAdvance pos buf
                 let sizeOnly = fromIntegral ((sizeAndType `shiftR` 4) .&. 0x0f) :: Int
@@ -959,7 +903,6 @@
                     buf
                     pos
                     identifier
-                    fieldStack
             3 -> do
                 sizeAndType <- readAndAdvance pos buf
                 let sizeOnly = fromIntegral ((sizeAndType `shiftR` 4) .&. 0x0f) :: Int
@@ -971,7 +914,6 @@
                     buf
                     pos
                     identifier
-                    fieldStack
             _ -> error "Unknown size statistics"
 
 footerSize :: Int
@@ -990,68 +932,63 @@
     | otherwise = error ("Unknown type in schema: " ++ show n)
 
 readLogicalType ::
-    BS.ByteString -> IORef Int -> Int16 -> [Int16] -> IO LogicalType
-readLogicalType buf pos lastFieldId fieldStack = do
-    t <- readAndAdvance pos buf
-    if t .&. 0x0f == 0
-        then return LOGICAL_TYPE_UNKNOWN
-        else do
-            let modifier = fromIntegral ((t .&. 0xf0) `shiftR` 4) :: Int16
-            identifier <-
-                if modifier == 0
-                    then readIntFromBuffer @Int16 buf pos
-                    else return (lastFieldId + modifier)
-            let _elemType = toTType (t .&. 0x0f)
-            case identifier of
-                1 -> do
-                    replicateM_ 2 (readField buf pos 0 [])
-                    return STRING_TYPE
-                2 -> do
-                    replicateM_ 2 (readField buf pos 0 [])
-                    return MAP_TYPE
-                3 -> do
-                    replicateM_ 2 (readField buf pos 0 [])
-                    return LIST_TYPE
-                4 -> do
-                    replicateM_ 2 (readField buf pos 0 [])
-                    return ENUM_TYPE
-                5 -> do
-                    readDecimalType 0 0 buf pos 0 []
-                6 -> do
-                    replicateM_ 2 (readField buf pos 0 [])
-                    return DATE_TYPE
-                7 -> do
-                    readTimeType False MILLISECONDS buf pos 0 []
-                8 -> do
-                    readTimestampType False MILLISECONDS buf pos 0 []
-                -- Apparently reserved for interval types
-                9 -> return LOGICAL_TYPE_UNKNOWN
-                10 -> do
-                    intType <- readIntType 0 False buf pos 0 []
-                    _ <- readField buf pos 0 []
-                    pure intType
-                11 -> do
-                    replicateM_ 2 (readField buf pos 0 [])
-                    return LOGICAL_TYPE_UNKNOWN
-                12 -> do
-                    replicateM_ 2 (readField buf pos 0 [])
-                    return JSON_TYPE
-                13 -> do
-                    replicateM_ 2 (readField buf pos 0 [])
-                    return BSON_TYPE
-                14 -> do
-                    replicateM_ 2 (readField buf pos 0 [])
-                    return UUID_TYPE
-                15 -> do
-                    replicateM_ 2 (readField buf pos 0 [])
-                    return FLOAT16_TYPE
-                16 -> do
-                    return VariantType{specificationVersion = 1}
-                17 -> do
-                    return GeometryType{crs = ""}
-                18 -> do
-                    return GeographyType{crs = "", algorithm = SPHERICAL}
-                _ -> return LOGICAL_TYPE_UNKNOWN
+    LogicalType -> BS.ByteString -> IORef Int -> Int16 -> IO LogicalType
+readLogicalType logicalType buf pos lastFieldId = do
+    fieldContents <- readField buf pos lastFieldId
+    case fieldContents of
+        Nothing -> pure logicalType
+        Just (elemType, identifier) -> case identifier of
+            1 -> do
+                -- This is an empty enum and is read as a field.
+                _ <- readField buf pos 0
+                readLogicalType STRING_TYPE buf pos identifier
+            2 -> do
+                _ <- readField buf pos 0
+                readLogicalType MAP_TYPE buf pos identifier
+            3 -> do
+                _ <- readField buf pos 0
+                readLogicalType LIST_TYPE buf pos identifier
+            4 -> do
+                _ <- readField buf pos 0
+                readLogicalType ENUM_TYPE buf pos identifier
+            5 -> do
+                decimal <- readDecimalType 0 0 buf pos 0
+                readLogicalType decimal buf pos identifier
+            6 -> do
+                _ <- readField buf pos 0
+                readLogicalType DATE_TYPE buf pos identifier
+            7 -> do
+                time <- readTimeType False MILLISECONDS buf pos 0
+                readLogicalType time buf pos identifier
+            8 -> do
+                timestamp <- readTimestampType False MILLISECONDS buf pos 0
+                readLogicalType timestamp buf pos identifier
+            -- Apparently reserved for interval types
+            9 -> do
+                _ <- readField buf pos 0
+                readLogicalType LOGICAL_TYPE_UNKNOWN buf pos identifier
+            10 -> do
+                intType <- readIntType 0 False buf pos 0
+                readLogicalType intType buf pos identifier
+            11 -> do
+                _ <- readField buf pos 0
+                readLogicalType LOGICAL_TYPE_UNKNOWN buf pos identifier
+            12 -> do
+                _ <- readField buf pos 0
+                readLogicalType JSON_TYPE buf pos identifier
+            13 -> do
+                _ <- readField buf pos 0
+                readLogicalType BSON_TYPE buf pos identifier
+            14 -> do
+                _ <- readField buf pos 0
+                readLogicalType UUID_TYPE buf pos identifier
+            15 -> do
+                _ <- readField buf pos 0
+                readLogicalType FLOAT16_TYPE buf pos identifier
+            16 -> error "Variant fields are unsupported"
+            17 -> error "Geometry fields are unsupported"
+            18 -> error "Geography fields are unsupported"
+            n -> error $ "Unknown logical type field: " ++ show n
 
 readIntType ::
     Int8 ->
@@ -1059,9 +996,8 @@
     BS.ByteString ->
     IORef Int ->
     Int16 ->
-    [Int16] ->
     IO LogicalType
-readIntType bitWidth intIsSigned buf pos lastFieldId fieldStack = do
+readIntType bitWidth intIsSigned buf pos lastFieldId = do
     t <- readAndAdvance pos buf
     if t .&. 0x0f == 0
         then return (IntType bitWidth intIsSigned)
@@ -1075,10 +1011,10 @@
             case identifier of
                 1 -> do
                     bitWidth' <- readAndAdvance pos buf
-                    readIntType (fromIntegral bitWidth') intIsSigned buf pos identifier fieldStack
+                    readIntType (fromIntegral bitWidth') intIsSigned buf pos identifier
                 2 -> do
                     let intIsSigned' = (t .&. 0x0f) == compactBooleanTrue
-                    readIntType bitWidth intIsSigned' buf pos identifier fieldStack
+                    readIntType bitWidth intIsSigned' buf pos identifier
                 _ -> error $ "UNKNOWN field ID for IntType: " ++ show identifier
 
 readDecimalType ::
@@ -1087,19 +1023,18 @@
     BS.ByteString ->
     IORef Int ->
     Int16 ->
-    [Int16] ->
     IO LogicalType
-readDecimalType precision scale buf pos lastFieldId fieldStack = do
-    fieldContents <- readField buf pos lastFieldId fieldStack
+readDecimalType precision scale buf pos lastFieldId = do
+    fieldContents <- readField buf pos lastFieldId
     case fieldContents of
         Nothing -> return (DecimalType precision scale)
         Just (elemType, identifier) -> case identifier of
             1 -> do
                 scale' <- readInt32FromBuffer buf pos
-                readDecimalType precision scale' buf pos lastFieldId fieldStack
+                readDecimalType precision scale' buf pos lastFieldId
             2 -> do
                 precision' <- readInt32FromBuffer buf pos
-                readDecimalType precision' scale buf pos lastFieldId fieldStack
+                readDecimalType precision' scale buf pos lastFieldId
             _ -> error $ "UNKNOWN field ID for DecimalType" ++ show identifier
 
 readTimeType ::
@@ -1108,20 +1043,19 @@
     BS.ByteString ->
     IORef Int ->
     Int16 ->
-    [Int16] ->
     IO LogicalType
-readTimeType isAdjustedToUTC unit buf pos lastFieldId fieldStack = do
-    fieldContents <- readField buf pos lastFieldId fieldStack
+readTimeType isAdjustedToUTC unit buf pos lastFieldId = do
+    fieldContents <- readField buf pos lastFieldId
     case fieldContents of
         Nothing -> return (TimeType isAdjustedToUTC unit)
         Just (elemType, identifier) -> case identifier of
             1 -> do
                 -- TODO: Check for empty
                 isAdjustedToUTC' <- (== compactBooleanTrue) <$> readAndAdvance pos buf
-                readTimeType isAdjustedToUTC' unit buf pos lastFieldId fieldStack
+                readTimeType isAdjustedToUTC' unit buf pos lastFieldId
             2 -> do
-                unit' <- readUnit buf pos 0 []
-                readTimeType isAdjustedToUTC unit' buf pos lastFieldId fieldStack
+                unit' <- readUnit TIME_UNIT_UNKNOWN buf pos 0
+                readTimeType isAdjustedToUTC unit' buf pos lastFieldId
             _ -> error $ "UNKNOWN field ID for TimeType" ++ show identifier
 
 readTimestampType ::
@@ -1130,35 +1064,32 @@
     BS.ByteString ->
     IORef Int ->
     Int16 ->
-    [Int16] ->
     IO LogicalType
-readTimestampType isAdjustedToUTC unit buf pos lastFieldId fieldStack = do
-    fieldContents <- readField buf pos lastFieldId fieldStack
+readTimestampType isAdjustedToUTC unit buf pos lastFieldId = do
+    fieldContents <- readField buf pos lastFieldId
     case fieldContents of
         Nothing -> return (TimestampType isAdjustedToUTC unit)
         Just (elemType, identifier) -> case identifier of
             1 -> do
                 -- TODO: Check for empty
-                isAdjustedToUTC' <- (== compactBooleanTrue) <$> readAndAdvance pos buf
-                readTimestampType isAdjustedToUTC' unit buf pos lastFieldId fieldStack
+                isAdjustedToUTC' <- (== compactBooleanTrue) <$> readNoAdvance pos buf
+                readTimestampType False unit buf pos lastFieldId
             2 -> do
-                unit' <- readUnit buf pos 0 []
-                readTimestampType isAdjustedToUTC unit' buf pos lastFieldId fieldStack
+                _ <- readField buf pos identifier
+                unit' <- readUnit TIME_UNIT_UNKNOWN buf pos 0
+                readTimestampType isAdjustedToUTC unit' buf pos lastFieldId
             _ -> error $ "UNKNOWN field ID for TimestampType" ++ show identifier
 
-readUnit :: BS.ByteString -> IORef Int -> Int16 -> [Int16] -> IO TimeUnit
-readUnit buf pos lastFieldId fieldStack = do
-    fieldContents <- readField buf pos lastFieldId fieldStack
+readUnit :: TimeUnit -> BS.ByteString -> IORef Int -> Int16 -> IO TimeUnit
+readUnit unit buf pos lastFieldId = do
+    fieldContents <- readField buf pos lastFieldId
     case fieldContents of
-        Nothing -> return TIME_UNIT_UNKNOWN
+        Nothing -> return unit
         Just (elemType, identifier) -> case identifier of
             1 -> do
-                _ <- readField buf pos 0 []
-                return MILLISECONDS
+                readUnit MILLISECONDS buf pos identifier
             2 -> do
-                _ <- readField buf pos 0 []
-                return MICROSECONDS
+                readUnit MICROSECONDS buf pos identifier
             3 -> do
-                _ <- readField buf pos 0 []
-                return NANOSECONDS
-            _ -> return TIME_UNIT_UNKNOWN
+                readUnit NANOSECONDS buf pos identifier
+            n -> error $ "Unknown time unit: " ++ show n
diff --git a/src/DataFrame/Monad.hs b/src/DataFrame/Monad.hs
--- a/src/DataFrame/Monad.hs
+++ b/src/DataFrame/Monad.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE ExplicitNamespaces #-}
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE GADTs #-}
+{-# LANGUAGE InstanceSigs #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TupleSections #-}
@@ -10,7 +11,7 @@
 import DataFrame (DataFrame)
 import qualified DataFrame as D
 import DataFrame.Internal.Column (Columnable)
-import DataFrame.Internal.Expression (Expr)
+import DataFrame.Internal.Expression (Expr (..))
 
 import qualified Data.Text as T
 
@@ -20,31 +21,60 @@
 newtype FrameM a = FrameM {runFrameM_ :: DataFrame -> (DataFrame, a)}
 
 instance Functor FrameM where
+    fmap :: (a -> b) -> FrameM a -> FrameM b
     fmap f (FrameM g) = FrameM $ \df ->
         let (df', x) = g df
          in (df', f x)
 
 instance Applicative FrameM where
     pure x = FrameM (,x)
+    (<*>) :: FrameM (a -> b) -> FrameM a -> FrameM b
     FrameM ff <*> FrameM fx = FrameM $ \df ->
         let (df1, f) = ff df
             (df2, x) = fx df1
          in (df2, f x)
 
 instance Monad FrameM where
+    (>>=) :: FrameM a -> (a -> FrameM b) -> FrameM b
     FrameM g >>= f = FrameM $ \df ->
         let (df1, x) = g df
             FrameM h = f x
          in h df1
 
+modifyM :: (DataFrame -> DataFrame) -> FrameM ()
+modifyM f = FrameM $ \df -> (f df, ())
+
+inspectM :: (DataFrame -> b) -> FrameM b
+inspectM f = FrameM $ \df -> (df, f df)
+
 deriveM :: (Columnable a) => T.Text -> Expr a -> FrameM (Expr a)
 deriveM name expr = FrameM $ \df ->
     let df' = D.derive name expr df
-     in (df', expr) -- or (df', F.col @a name)
+     in (df', Col name)
 
 filterWhereM :: Expr Bool -> FrameM ()
-filterWhereM p = FrameM $ \df ->
-    (D.filterWhere p df, ())
+filterWhereM p = modifyM (D.filterWhere p)
 
-runFrameM :: DataFrame -> FrameM a -> DataFrame
-runFrameM df action = fst (runFrameM_ action df)
+filterJustM :: (Columnable a) => Expr (Maybe a) -> FrameM (Expr a)
+filterJustM (Col name) = FrameM $ \df ->
+    let df' = D.filterJust name df
+     in (df', Col name)
+filterJustM expr =
+    error $ "Cannot filter on compound expression: " ++ show expr
+
+imputeM :: (Columnable a) => Expr (Maybe a) -> a -> FrameM (Expr a)
+imputeM expr@(Col name) value = FrameM $ \df ->
+    let df' = D.impute expr value df
+     in (df', Col name)
+imputeM expr _ = error $ "Cannot impute on compound expression: " ++ show expr
+
+runFrameM :: DataFrame -> FrameM a -> (a, DataFrame)
+runFrameM df (FrameM action) =
+    let (df', a) = action df
+     in (a, df')
+
+evalFrameM :: DataFrame -> FrameM a -> a
+evalFrameM df m = fst (runFrameM df m)
+
+execFrameM :: DataFrame -> FrameM a -> DataFrame
+execFrameM df m = snd (runFrameM df m)
diff --git a/src/DataFrame/Operations/Core.hs b/src/DataFrame/Operations/Core.hs
--- a/src/DataFrame/Operations/Core.hs
+++ b/src/DataFrame/Operations/Core.hs
@@ -31,8 +31,17 @@
     expandColumn,
     fromList,
     fromVector,
+    toDoubleVector,
+    toFloatVector,
+    toIntVector,
+    toUnboxedVector,
  )
-import DataFrame.Internal.DataFrame (DataFrame (..), empty, getColumn)
+import DataFrame.Internal.DataFrame (
+    DataFrame (..),
+    empty,
+    getColumn,
+    unsafeGetColumn,
+ )
 import DataFrame.Internal.Expression
 import DataFrame.Internal.Parsing (isNullish)
 import DataFrame.Internal.Row (Any, mkColumnFromRow)
@@ -749,3 +758,169 @@
 -}
 fold :: (a -> DataFrame -> DataFrame) -> [a] -> DataFrame -> DataFrame
 fold f xs acc = L.foldl' (flip f) acc xs
+
+{- | Returns a dataframe as a two dimensional vector of floats.
+
+Converts all columns in the dataframe to float vectors and transposes them
+into a row-major matrix representation.
+
+This is useful for handing data over into ML systems.
+
+Returns 'Left' with an error if any column cannot be converted to floats.
+-}
+toFloatMatrix ::
+    DataFrame -> Either DataFrameException (V.Vector (VU.Vector Float))
+toFloatMatrix df = case V.foldl'
+    (\acc c -> V.snoc <$> acc <*> toFloatVector c)
+    (Right V.empty :: Either DataFrameException (V.Vector (VU.Vector Float)))
+    (columns df) of
+    Left e -> Left e
+    Right m ->
+        pure $
+            V.generate
+                (fst (dataframeDimensions df))
+                ( \i ->
+                    foldl
+                        (\acc j -> acc `VU.snoc` ((m VG.! j) VG.! i))
+                        VU.empty
+                        [0 .. (V.length m - 1)]
+                )
+
+{- | Returns a dataframe as a two dimensional vector of doubles.
+
+Converts all columns in the dataframe to double vectors and transposes them
+into a row-major matrix representation.
+
+This is useful for handing data over into ML systems.
+
+Returns 'Left' with an error if any column cannot be converted to doubles.
+-}
+toDoubleMatrix ::
+    DataFrame -> Either DataFrameException (V.Vector (VU.Vector Double))
+toDoubleMatrix df = case V.foldl'
+    (\acc c -> V.snoc <$> acc <*> toDoubleVector c)
+    (Right V.empty :: Either DataFrameException (V.Vector (VU.Vector Double)))
+    (columns df) of
+    Left e -> Left e
+    Right m ->
+        pure $
+            V.generate
+                (fst (dataframeDimensions df))
+                ( \i ->
+                    foldl
+                        (\acc j -> acc `VU.snoc` ((m VG.! j) VG.! i))
+                        VU.empty
+                        [0 .. (V.length m - 1)]
+                )
+
+{- | Returns a dataframe as a two dimensional vector of ints.
+
+Converts all columns in the dataframe to int vectors and transposes them
+into a row-major matrix representation.
+
+This is useful for handing data over into ML systems.
+
+Returns 'Left' with an error if any column cannot be converted to ints.
+-}
+toIntMatrix :: DataFrame -> Either DataFrameException (V.Vector (VU.Vector Int))
+toIntMatrix df = case V.foldl'
+    (\acc c -> V.snoc <$> acc <*> toIntVector c)
+    (Right V.empty :: Either DataFrameException (V.Vector (VU.Vector Int)))
+    (columns df) of
+    Left e -> Left e
+    Right m ->
+        pure $
+            V.generate
+                (fst (dataframeDimensions df))
+                ( \i ->
+                    foldl
+                        (\acc j -> acc `VU.snoc` ((m VG.! j) VG.! i))
+                        VU.empty
+                        [0 .. (V.length m - 1)]
+                )
+
+{- | Get a specific column as a vector.
+
+You must specify the type via type applications.
+
+==== __Examples__
+
+>>> columnAsVector @Int "age" df
+[25, 30, 35, ...]
+
+>>> columnAsVector @Text "name" df
+["Alice", "Bob", "Charlie", ...]
+
+==== __Throws__
+
+* 'error' - if the column type doesn't match the requested type
+-}
+columnAsVector :: forall a. (Columnable a) => Expr a -> DataFrame -> V.Vector a
+columnAsVector (Col name) df = case unsafeGetColumn name df of
+    (BoxedColumn (col :: V.Vector b)) -> case testEquality (typeRep @a) (typeRep @b) of
+        Nothing -> error "Type error"
+        Just Refl -> col
+    (OptionalColumn (col :: V.Vector b)) -> case testEquality (typeRep @a) (typeRep @b) of
+        Nothing -> error "Type error"
+        Just Refl -> col
+    (UnboxedColumn (col :: VU.Vector b)) -> case testEquality (typeRep @a) (typeRep @b) of
+        Nothing -> error "Type error"
+        Just Refl -> VG.convert col
+columnAsVector _ _ = error "UNIMPLEMENTED"
+
+{- | Retrieves a column as an unboxed vector of 'Int' values.
+
+Returns 'Left' with a 'DataFrameException' if the column cannot be converted to ints.
+This may occur if the column contains non-numeric data or values outside the 'Int' range.
+-}
+columnAsIntVector ::
+    Expr Int -> DataFrame -> Either DataFrameException (VU.Vector Int)
+columnAsIntVector (Col name) df = toIntVector (unsafeGetColumn name df)
+columnAsIntVector _ _ = error "UNIMPLEMENTED"
+
+{- | Retrieves a column as an unboxed vector of 'Double' values.
+
+Returns 'Left' with a 'DataFrameException' if the column cannot be converted to doubles.
+This may occur if the column contains non-numeric data.
+-}
+columnAsDoubleVector ::
+    Expr Double -> DataFrame -> Either DataFrameException (VU.Vector Double)
+columnAsDoubleVector (Col name) df = toDoubleVector (unsafeGetColumn name df)
+columnAsDoubleVector _ _ = error "UNIMPLEMENTED"
+
+{- | Retrieves a column as an unboxed vector of 'Float' values.
+
+Returns 'Left' with a 'DataFrameException' if the column cannot be converted to floats.
+This may occur if the column contains non-numeric data.
+-}
+columnAsFloatVector ::
+    Expr Float -> DataFrame -> Either DataFrameException (VU.Vector Float)
+columnAsFloatVector (Col name) df = toFloatVector (unsafeGetColumn name df)
+columnAsFloatVector _ _ = error "UNIMPLEMENTED"
+
+columnAsUnboxedVector ::
+    forall a.
+    (Columnable a, VU.Unbox a) =>
+    Expr a -> DataFrame -> Either DataFrameException (VU.Vector a)
+columnAsUnboxedVector (Col name) df = toUnboxedVector @a (unsafeGetColumn name df)
+columnAsUnboxedVector _ _ = error "UNIMPLEMENTED"
+
+{- | Get a specific column as a list.
+
+You must specify the type via type applications.
+
+==== __Examples__
+
+>>> columnAsList @Int "age" df
+[25, 30, 35, ...]
+
+>>> columnAsList @Text "name" df
+["Alice", "Bob", "Charlie", ...]
+
+==== __Throws__
+
+* 'error' - if the column type doesn't match the requested type
+-}
+columnAsList :: forall a. (Columnable a) => Expr a -> DataFrame -> [a]
+columnAsList expr@(Col name) df = V.toList (columnAsVector expr df)
+columnAsList _ _ = error "UNIMPLEMENTED"
diff --git a/src/DataFrame/Operations/Statistics.hs b/src/DataFrame/Operations/Statistics.hs
--- a/src/DataFrame/Operations/Statistics.hs
+++ b/src/DataFrame/Operations/Statistics.hs
@@ -25,8 +25,6 @@
 import DataFrame.Internal.Column
 import DataFrame.Internal.DataFrame (
     DataFrame (..),
-    columnAsUnboxedVector,
-    columnAsVector,
     empty,
     getColumn,
  )
@@ -89,7 +87,7 @@
 -- | Calculates the mean of a given column as a standalone value.
 mean ::
     forall a. (Columnable a, Real a, VU.Unbox a) => Expr a -> DataFrame -> Double
-mean (Col name) df = case columnAsUnboxedVector @a name df of
+mean (Col name) df = case columnAsUnboxedVector (Col @a name) df of
     Right xs -> mean' xs
     Left e -> throw e
 mean expr df = case interpret df expr of
@@ -100,7 +98,7 @@
 
 meanMaybe ::
     forall a. (Columnable a, Real a) => Expr (Maybe a) -> DataFrame -> Double
-meanMaybe (Col name) df = (mean' . optionalToDoubleVector) (columnAsVector @(Maybe a) name df)
+meanMaybe (Col name) df = (mean' . optionalToDoubleVector) (columnAsVector (Col @(Maybe a) name) df)
 meanMaybe expr df = case interpret @(Maybe a) df expr of
     Left e -> throw e
     Right (TColumn col) -> case toVector @(Maybe a) col of
@@ -110,7 +108,7 @@
 -- | Calculates the median of a given column as a standalone value.
 median ::
     forall a. (Columnable a, Real a, VU.Unbox a) => Expr a -> DataFrame -> Double
-median (Col name) df = case columnAsUnboxedVector @a name df of
+median (Col name) df = case columnAsUnboxedVector (Col @a name) df of
     Right xs -> median' xs
     Left e -> throw e
 median expr df = case interpret df expr of
@@ -122,7 +120,7 @@
 -- | Calculates the standard deviation of a given column as a standalone value.
 standardDeviation ::
     forall a. (Columnable a, Real a, VU.Unbox a) => Expr a -> DataFrame -> Double
-standardDeviation (Col name) df = case columnAsUnboxedVector @a name df of
+standardDeviation (Col name) df = case columnAsUnboxedVector (Col @a name) df of
     Right xs -> (sqrt . variance') xs
     Left e -> throw e
 standardDeviation expr df = case interpret df expr of
@@ -134,7 +132,7 @@
 -- | Calculates the skewness of a given column as a standalone value.
 skewness ::
     forall a. (Columnable a, Real a, VU.Unbox a) => Expr a -> DataFrame -> Double
-skewness (Col name) df = case columnAsUnboxedVector @a name df of
+skewness (Col name) df = case columnAsUnboxedVector (Col @a name) df of
     Right xs -> skewness' xs
     Left e -> throw e
 skewness expr df = case interpret df expr of
@@ -146,7 +144,7 @@
 -- | Calculates the variance of a given column as a standalone value.
 variance ::
     forall a. (Columnable a, Real a, VU.Unbox a) => Expr a -> DataFrame -> Double
-variance (Col name) df = case columnAsUnboxedVector @a name df of
+variance (Col name) df = case columnAsUnboxedVector (Col @a name) df of
     Right xs -> variance' xs
     Left e -> throw e
 variance expr df = case interpret df expr of
@@ -158,7 +156,7 @@
 -- | Calculates the inter-quartile range of a given column as a standalone value.
 interQuartileRange ::
     forall a. (Columnable a, Real a, VU.Unbox a) => Expr a -> DataFrame -> Double
-interQuartileRange (Col name) df = case columnAsUnboxedVector @a name df of
+interQuartileRange (Col name) df = case columnAsUnboxedVector (Col @a name) df of
     Right xs -> interQuartileRange' xs
     Left e -> throw e
 interQuartileRange expr df = case interpret df expr of
diff --git a/src/DataFrame/Synthesis.hs b/src/DataFrame/Synthesis.hs
--- a/src/DataFrame/Synthesis.hs
+++ b/src/DataFrame/Synthesis.hs
@@ -22,11 +22,10 @@
     Expr (..),
     eSize,
     interpret,
-    replaceExpr,
  )
 import DataFrame.Internal.Statistics
 import qualified DataFrame.Operations.Statistics as Stats
-import DataFrame.Operations.Subset (exclude, select)
+import DataFrame.Operations.Subset (exclude)
 
 import Control.Exception (throw)
 import Data.Containers.ListUtils
@@ -40,7 +39,6 @@
 import qualified Data.Vector.Unboxed as VU
 import DataFrame.Functions ((.&&), (.<=), (.>), (.||))
 import qualified DataFrame.Operations.Core as D
-import qualified DataFrame.Operations.Transformations as D
 import Debug.Trace (trace)
 import Type.Reflection (typeRep)
 
@@ -80,6 +78,7 @@
         existingPrograms
             ++ [ transform p
                | p <- ps ++ vars
+               , Prelude.not (isConditional p)
                , transform <-
                     [ sqrt
                     , abs
@@ -93,20 +92,30 @@
                ]
             ++ [ F.pow p i
                | p <- existingPrograms
+               , Prelude.not (isConditional p)
                , i <- [2 .. 6]
                ]
             ++ [ p + q
                | (i, p) <- zip [0 ..] existingPrograms
                , (j, q) <- zip [0 ..] existingPrograms
                , Prelude.not (isLiteral p && isLiteral q)
+               , Prelude.not (isConditional p || isConditional q)
                , i >= j
                ]
+            ++ [ p - q
+               | (i, p) <- zip [0 ..] existingPrograms
+               , (j, q) <- zip [0 ..] existingPrograms
+               , Prelude.not (isLiteral p && isLiteral q)
+               , Prelude.not (isConditional p || isConditional q)
+               , i /= j
+               ]
             ++ ( if includeConds
                     then
                         [ F.min p q
                         | (i, p) <- zip [0 ..] existingPrograms
                         , (j, q) <- zip [0 ..] existingPrograms
                         , Prelude.not (isLiteral p && isLiteral q)
+                        , Prelude.not (isConditional p || isConditional q)
                         , p /= q
                         , i > j
                         ]
@@ -114,6 +123,7 @@
                                | (i, p) <- zip [0 ..] existingPrograms
                                , (j, q) <- zip [0 ..] existingPrograms
                                , Prelude.not (isLiteral p && isLiteral q)
+                               , Prelude.not (isConditional p || isConditional q)
                                , p /= q
                                , i > j
                                ]
@@ -121,26 +131,23 @@
                                | cond <- conds
                                , r <- existingPrograms
                                , s <- existingPrograms
+                               , Prelude.not (isConditional r || isConditional s)
                                , r /= s
                                ]
                     else []
                )
-            ++ [ p - q
-               | (i, p) <- zip [0 ..] existingPrograms
-               , (j, q) <- zip [0 ..] existingPrograms
-               , Prelude.not (isLiteral p && isLiteral q)
-               , i /= j
-               ]
             ++ [ p * q
                | (i, p) <- zip [0 ..] existingPrograms
                , (j, q) <- zip [0 ..] existingPrograms
                , Prelude.not (isLiteral p && isLiteral q)
+               , Prelude.not (isConditional p || isConditional q)
                , i >= j
                ]
             ++ [ p / q
                | p <- existingPrograms
                , q <- existingPrograms
                , Prelude.not (isLiteral p && isLiteral q)
+               , Prelude.not (isConditional p || isConditional q)
                , p /= q
                ]
 
@@ -148,6 +155,10 @@
 isLiteral (Lit _) = True
 isLiteral _ = False
 
+isConditional :: Expr a -> Bool
+isConditional (If{}) = True
+isConditional _ = False
+
 deduplicate ::
     forall a.
     (Columnable a) =>
@@ -289,34 +300,12 @@
         t = case interpret df (Col target) of
             Left e -> throw e
             Right v -> v
+        cfg = BeamConfig d b MeanSquaredError True
+        constants = percentiles df' ++ [Lit 10, Lit 1, Lit 0.1, Lit targetMean]
      in
-        case beamSearch
-            df'
-            ( BeamConfig
-                d
-                b
-                MutualInformation
-                False
-            )
-            t
-            (percentiles df')
-            []
-            [] of
+        case beamSearch df' cfg t constants [] [] of
             Nothing -> Left "No programs found"
-            Just p ->
-                trace (show p) $
-                    let
-                     in case beamSearch
-                            ( D.derive "_generated_regression_feature_" p df
-                                & select ["_generated_regression_feature_"]
-                            )
-                            (BeamConfig d b MeanSquaredError False)
-                            t
-                            (percentiles df' ++ [Lit targetMean, Lit 10])
-                            []
-                            [Col "_generated_regression_feature_"] of
-                            Nothing -> Left "Could not find coefficients"
-                            Just p' -> Right (replaceExpr p (Col @Double "_generated_regression_feature_") p')
+            Just p -> Right p
 
 data LossFunction
     = PearsonCorrelation
@@ -375,7 +364,7 @@
             (generatePrograms (includeConditionals cfg) conditions vars constants ps)
   where
     vars = map Col names
-    conditions = generateConditions outputs conds (vars ++ constants ++ ps) df
+    conditions = generateConditions outputs conds vars df
     ps = pickTopN df outputs cfg $ deduplicate df programs
     names = (map fst . L.sortBy (compare `on` snd) . M.toList . columnIndices) df
 
diff --git a/tests/Functions.hs b/tests/Functions.hs
--- a/tests/Functions.hs
+++ b/tests/Functions.hs
@@ -6,9 +6,11 @@
 import qualified DataFrame as D
 import DataFrame.Functions (
     sanitize,
+    (.>),
  )
 import qualified DataFrame.Functions as F
 import qualified DataFrame.Internal.Column as DI
+import DataFrame.Internal.Expression
 import Test.HUnit
 
 -- Test cases for the sanitize function
@@ -79,8 +81,48 @@
             (D.derive "sum" (F.sum (F.col @Int "A")) df)
         )
 
+testGtTwoLitsRewriteAsLit :: Test
+testGtTwoLitsRewriteAsLit =
+    TestCase
+        ( assertEqual
+            "Two lits rewrite as one"
+            (Lit True)
+            (Lit (5 :: Int) .> Lit 4)
+        )
+
+testGtLeftLitRewriteAsUnary :: Test
+testGtLeftLitRewriteAsUnary =
+    TestCase
+        ( assertEqual
+            "Two lits rewrite as single literal"
+            (UnaryOp "gt 5" ((5 :: Int) >) (Col "x"))
+            (Lit (5 :: Int) .> Col "x")
+        )
+
+testGtRightLitRewriteAsUnary :: Test
+testGtRightLitRewriteAsUnary =
+    TestCase
+        ( assertEqual
+            "Two lits rewrite as unary op"
+            (UnaryOp "gt 5" ((5 :: Int) >) (Col "x"))
+            (Lit (5 :: Int) .> Col "x")
+        )
+
+testGtNoLitWriteAsBinary :: Test
+testGtNoLitWriteAsBinary =
+    TestCase
+        ( assertEqual
+            "Two lits rewrite as unary op"
+            (BinaryOp "gt" (>) (Col @Int "x") (Col "y"))
+            (Col @Int "x" .> Col "y")
+        )
+
 tests :: [Test]
 tests =
     [ TestLabel "sanitizeIdentifiers" sanitizeIdentifiers
     , TestLabel "testSum" testSum
+    , TestLabel "testGtTwoLitRewrite" testGtTwoLitsRewriteAsLit
+    , TestLabel "testGtLeftLit" testGtLeftLitRewriteAsUnary
+    , TestLabel "testGtRightLit" testGtRightLitRewriteAsUnary
+    , TestLabel "testGtNoLit" testGtNoLitWriteAsBinary
     ]