diff --git a/ChangeLog.markdown b/ChangeLog.markdown
--- a/ChangeLog.markdown
+++ b/ChangeLog.markdown
@@ -1,3 +1,16 @@
+v3.19.2
+--------
+
+New Features:
+
+- Allow a `default` thunk to be passed to `hash-table-ref`.
+- Added `hash-table-ref/default`.
+
+Bug Fixes:
+
+- Fixed `rational?` to properly handle floating-point numbers.
+- Migrated `string-fill!` from a macro to a function. This makes it easier to redefine, for example per SRFI 13.
+
 v3.19.1
 --------
 
diff --git a/hs-src/Language/Scheme/Core.hs b/hs-src/Language/Scheme/Core.hs
--- a/hs-src/Language/Scheme/Core.hs
+++ b/hs-src/Language/Scheme/Core.hs
@@ -43,6 +43,7 @@
     , updateList
     , updateVector
     , updateByteVector
+    , hashTblRef
     -- * Error handling
     , addToCallHistory
     , throwErrorWithCallHistory
@@ -87,7 +88,7 @@
   putStrLn " |_| |_|\\__,_|___/_|\\_\\  ///   \\\\\\  |___/\\___|_| |_|\\___|_| |_| |_|\\___| "
   putStrLn "                                                                         "
   putStrLn " http://justinethier.github.io/husk-scheme                              "
-  putStrLn " (c) 2010-2015 Justin Ethier                                             "
+  putStrLn " (c) 2010-2016 Justin Ethier                                             "
   putStrLn $ " Version " ++ (DV.showVersion PHS.version) ++ " "
   putStrLn "                                                                         "
 
@@ -1075,7 +1076,7 @@
 nullEnvWithImport = nullEnv >>= 
   (flip extendEnv [
     ((varNamespace, "%import"), EvalFunc evalfuncImport),
-    ((varNamespace, "hash-table-ref"), IOFunc $ wrapHashTbl hashTblRef)])
+    ((varNamespace, "hash-table-ref"), EvalFunc hashTblRef)])
 
 -- |Load the standard r5rs environment, including libraries
 r5rsEnv :: IO Env
@@ -1426,6 +1427,7 @@
                   , ("current-environment", evalfuncInteractionEnv)
                   , ("interaction-environment", evalfuncInteractionEnv)
                   , ("make-environment", evalfuncMakeEnv)
+                  , ("hash-table-ref", hashTblRef)
 
                -- Non-standard extensions
 #ifdef UseFfi
@@ -1452,3 +1454,34 @@
 addToCallHistory f history 
   | null history = [f]
   | otherwise = (lastN' 9 history) ++ [f]
+
+-- | Retrieve the value from the hashtable for the given key.
+--   An error is thrown if the key is not found.
+--
+--   Note this had to be made an EvalFunc because a thunk
+--   can be passed as an optional argument to be executed 
+--   if the key is not found.
+--
+--   Arguments:
+--
+--   * Current continuation
+--   * HashTable to copy
+--   * Object that is the key to query the table for
+--
+--   Returns: Object containing the key's value
+--
+hashTblRef :: [LispVal] -> IOThrowsError LispVal
+hashTblRef [_, (HashTable ht), key] = do
+  case Data.Map.lookup key ht of
+    Just val -> return val
+    Nothing -> throwError $ BadSpecialForm "Hash table does not contain key" key
+hashTblRef [cont, (HashTable ht), key, thunk] = do
+  case Data.Map.lookup key ht of
+    Just val -> return $ val
+    Nothing -> apply cont thunk []
+hashTblRef (cont : p@(Pointer _ _) : args) = do
+  ht <- derefPtr p
+  hashTblRef (cont : ht : args)
+hashTblRef [_, badType] = throwError $ TypeMismatch "hash-table" badType
+hashTblRef badArgList = throwError $ NumArgs (Just 2) (tail badArgList)
+
diff --git a/hs-src/Language/Scheme/Environments.hs b/hs-src/Language/Scheme/Environments.hs
--- a/hs-src/Language/Scheme/Environments.hs
+++ b/hs-src/Language/Scheme/Environments.hs
@@ -132,7 +132,6 @@
 
               ("hash-table?",       wrapHashTbl isHashTbl),
               ("hash-table-exists?",wrapHashTbl hashTblExists),
-              ("hash-table-ref",    wrapHashTbl hashTblRef),
               ("hash-table-size",   wrapHashTbl hashTblSize),
               ("hash-table->alist", wrapHashTbl hashTbl2List),
               ("hash-table-keys",   wrapHashTbl hashTblKeys),
diff --git a/hs-src/Language/Scheme/Numerical.hs b/hs-src/Language/Scheme/Numerical.hs
--- a/hs-src/Language/Scheme/Numerical.hs
+++ b/hs-src/Language/Scheme/Numerical.hs
@@ -613,8 +613,7 @@
 isRational :: [LispVal] -> ThrowsError LispVal
 isRational ([Number _]) = return $ Bool True
 isRational ([Rational _]) = return $ Bool True
-isRational ([n@(Float _)]) = return $ Bool $ isFloatAnInteger n
-                             -- FUTURE: not quite good enough, could be represented exactly and not an integer
+isRational ([Float n]) = return $ Bool $ not $ isInfinite n 
 isRational _ = return $ Bool False
 
 -- |Predicate to determine if given number is an integer.
diff --git a/hs-src/Language/Scheme/Primitives.hs b/hs-src/Language/Scheme/Primitives.hs
--- a/hs-src/Language/Scheme/Primitives.hs
+++ b/hs-src/Language/Scheme/Primitives.hs
@@ -44,7 +44,6 @@
  , byteVectorStr2Utf
  -- ** Hash Table
  , hashTblExists 
- , hashTblRef
  , hashTblSize 
  , hashTbl2List
  , hashTblKeys
@@ -1216,31 +1215,6 @@
     Nothing -> return $ Bool False
 hashTblExists [] = throwError $ NumArgs (Just 2) []
 hashTblExists args@(_ : _) = throwError $ NumArgs (Just 2) args
-
--- | Retrieve the value from the hashtable for the given key.
---   An error is thrown if the key is not found.
---
---   Arguments:
---
---   * HashTable to copy
---
---   * Object that is the key to query the table for
---
---   Returns: Object containing the key's value
---
-hashTblRef :: [LispVal] -> ThrowsError LispVal
-hashTblRef [(HashTable ht), key] = do
-  case Data.Map.lookup key ht of
-    Just val -> return val
-    Nothing -> throwError $ BadSpecialForm "Hash table does not contain key" key
-hashTblRef [(HashTable ht), key, Func {}] = do
-  case Data.Map.lookup key ht of
-    Just val -> return $ val
-    Nothing -> throwError $ NotImplemented "thunk"
-{- FUTURE: a thunk can optionally be specified, this drives definition of /default
-Nothing -> apply thunk [] -}
-hashTblRef [badType] = throwError $ TypeMismatch "hash-table" badType
-hashTblRef badArgList = throwError $ NumArgs (Just 2) badArgList
 
 -- | Return the number of key/value associations in the hashtable
 --
diff --git a/husk-scheme.cabal b/husk-scheme.cabal
--- a/husk-scheme.cabal
+++ b/husk-scheme.cabal
@@ -1,5 +1,5 @@
 Name:                husk-scheme
-Version:             3.19.1
+Version:             3.19.2
 Synopsis:            R5RS Scheme interpreter, compiler, and library.
 Description:         
   <<https://github.com/justinethier/husk-scheme/raw/master/docs/husk-scheme.png>>
diff --git a/lib/core.scm b/lib/core.scm
--- a/lib/core.scm
+++ b/lib/core.scm
@@ -331,11 +331,17 @@
 ; End delayed evaluation section
 
 ; String Section
-(define-syntax string-fill!
-  (syntax-rules ()
-    ((_ _str _chr)
-     (set! _str
-           (make-string (string-length _str) _chr)))))
+(define (string-fill! str fill . opts)
+  (letrec* ((len (string-length str))
+            (start (if (> (length opts) 0) (car opts) 0))
+            (end (if (> (length opts) 1) (cadr opts) len))
+            (loop (lambda (i)
+                    (cond
+                     ((= i end) str)
+                     (else
+                       (string-set! str i fill)
+                       (loop (+ i 1)))))))
+    (loop start)))
 
 (define (string-concatenate l) 
     (apply string-append l)) 
@@ -404,6 +410,9 @@
     (exit-fail))
 
 ;; Hashtable derived forms
+(define (hash-table-ref/default ht key default)
+  (hash-table-ref ht key (lambda () default)))
+
 (define hash-table-walk
   (lambda (ht proc)
     (map 
diff --git a/lib/srfi/69.sld b/lib/srfi/69.sld
--- a/lib/srfi/69.sld
+++ b/lib/srfi/69.sld
@@ -6,7 +6,7 @@
         ;hash-table-equivalence-function 
         ;hash-table-hash-function
         hash-table-ref 
-        ;hash-table-ref/default 
+        hash-table-ref/default 
         ;hash-table-set! 
         ;TODO: should implement this: hash-table-delete! 
         hash-table-exists?