th-desugar-1.6: Language/Haskell/TH/Desugar.hs
{- Language/Haskell/TH/Desugar.hs
(c) Richard Eisenberg 2013
eir@cis.upenn.edu
-}
{-# LANGUAGE CPP, MultiParamTypeClasses, FunctionalDependencies,
TypeSynonymInstances, FlexibleInstances #-}
-----------------------------------------------------------------------------
-- |
-- Module : Language.Haskell.TH.Desugar
-- Copyright : (C) 2014 Richard Eisenberg
-- License : BSD-style (see LICENSE)
-- Maintainer : Richard Eisenberg (eir@cis.upenn.edu)
-- Stability : experimental
-- Portability : non-portable
--
-- Desugars full Template Haskell syntax into a smaller core syntax for further
-- processing. The desugared types and constructors are prefixed with a D.
--
----------------------------------------------------------------------------
module Language.Haskell.TH.Desugar (
-- * Desugared data types
DExp(..), DLetDec(..), DPat(..), DType(..), DKind, DCxt, DPred(..),
DTyVarBndr(..), DMatch(..), DClause(..), DDec(..),
Overlap(..), NewOrData(..),
DTypeFamilyHead(..), DFamilyResultSig(..), InjectivityAnn(..),
DCon(..), DConFields(..), DBangType, DVarBangType,
Bang(..), SourceUnpackedness(..), SourceStrictness(..),
DForeign(..),
DPragma(..), DRuleBndr(..), DTySynEqn(..), DInfo(..), DInstanceDec,
Role(..), AnnTarget(..),
-- * The 'Desugar' class
Desugar(..),
-- * Main desugaring functions
dsExp, dsDecs, dsType, dsInfo,
dsPatOverExp, dsPatsOverExp, dsPatX,
dsLetDecs, dsTvb, dsCxt,
dsCon, dsForeign, dsPragma, dsRuleBndr,
-- ** Secondary desugaring functions
PatM, dsPred, dsPat, dsDec, dsLetDec,
dsMatches, dsBody, dsGuards, dsDoStmts, dsComp, dsClauses,
dsBangType, dsVarBangType,
#if __GLASGOW_HASKELL__ > 710
dsTypeFamilyHead, dsFamilyResultSig,
#endif
-- * Converting desugared AST back to TH AST
module Language.Haskell.TH.Desugar.Sweeten,
-- * Expanding type synonyms
expand, expandType,
-- * Reification
reifyWithWarning,
-- | The following definitions allow you to register a list of
-- @Dec@s to be used in reification queries.
withLocalDeclarations, dsReify, reifyWithLocals_maybe, reifyWithLocals,
DsMonad(..), DsM,
-- * Nested pattern flattening
scExp, scLetDec,
-- * Utility functions
applyDExp, applyDType,
dPatToDExp, removeWilds,
getDataD, dataConNameToDataName, dataConNameToCon,
nameOccursIn, allNamesIn, flattenDValD, getRecordSelectors,
mkTypeName, mkDataName, newUniqueName,
mkTupleDExp, mkTupleDPat, maybeDLetE, maybeDCaseE,
substTy,
tupleDegree_maybe, tupleNameDegree_maybe,
unboxedTupleDegree_maybe, unboxedTupleNameDegree_maybe,
strictToBang,
-- ** Extracting bound names
extractBoundNamesStmt, extractBoundNamesDec, extractBoundNamesPat
) where
import Language.Haskell.TH.Desugar.Core
import Language.Haskell.TH.Desugar.Util
import Language.Haskell.TH.Desugar.Sweeten
import Language.Haskell.TH.Syntax
import Language.Haskell.TH.Desugar.Reify
import Language.Haskell.TH.Desugar.Expand
import Language.Haskell.TH.Desugar.Match
import qualified Data.Set as S
#if __GLASGOW_HASKELL__ < 709
import Data.Foldable ( foldMap )
#endif
import Prelude hiding ( exp )
-- | This class relates a TH type with its th-desugar type and allows
-- conversions back and forth. The functional dependency goes only one
-- way because `Type` and `Kind` are type synonyms, but they desugar
-- to different types.
class Desugar th ds | ds -> th where
desugar :: DsMonad q => th -> q ds
sweeten :: ds -> th
instance Desugar Exp DExp where
desugar = dsExp
sweeten = expToTH
instance Desugar Type DType where
desugar = dsType
sweeten = typeToTH
instance Desugar Cxt DCxt where
desugar = dsCxt
sweeten = cxtToTH
instance Desugar TyVarBndr DTyVarBndr where
desugar = dsTvb
sweeten = tvbToTH
instance Desugar [Dec] [DDec] where
desugar = dsDecs
sweeten = decsToTH
instance Desugar [Con] [DCon] where
desugar = concatMapM dsCon
sweeten = map conToTH
-- | If the declaration passed in is a 'DValD', creates new, equivalent
-- declarations such that the 'DPat' in all 'DValD's is just a plain
-- 'DVarPa'. Other declarations are passed through unchanged.
-- Note that the declarations that come out of this function are rather
-- less efficient than those that come in: they have many more pattern
-- matches.
flattenDValD :: Quasi q => DLetDec -> q [DLetDec]
flattenDValD dec@(DValD (DVarPa _) _) = return [dec]
flattenDValD (DValD pat exp) = do
x <- newUniqueName "x" -- must use newUniqueName here because we might be top-level
let top_val_d = DValD (DVarPa x) exp
bound_names = S.elems $ extractBoundNamesDPat pat
other_val_ds <- mapM (mk_val_d x) bound_names
return $ top_val_d : other_val_ds
where
mk_val_d x name = do
y <- newUniqueName "y"
let pat' = wildify name y pat
match = DMatch pat' (DVarE y)
cas = DCaseE (DVarE x) [match]
return $ DValD (DVarPa name) cas
wildify name y p =
case p of
DLitPa lit -> DLitPa lit
DVarPa n
| n == name -> DVarPa y
| otherwise -> DWildPa
DConPa con ps -> DConPa con (map (wildify name y) ps)
DTildePa pa -> DTildePa (wildify name y pa)
DBangPa pa -> DBangPa (wildify name y pa)
DWildPa -> DWildPa
flattenDValD other_dec = return [other_dec]
extractBoundNamesDPat :: DPat -> S.Set Name
extractBoundNamesDPat (DLitPa _) = S.empty
extractBoundNamesDPat (DVarPa n) = S.singleton n
extractBoundNamesDPat (DConPa _ pats) = foldMap extractBoundNamesDPat pats
extractBoundNamesDPat (DTildePa pat) = extractBoundNamesDPat pat
extractBoundNamesDPat (DBangPa pat) = extractBoundNamesDPat pat
extractBoundNamesDPat DWildPa = S.empty
fvDType :: DType -> S.Set Name
fvDType = go
where
go (DForallT tvbs _cxt ty) = go ty `S.difference` (foldMap dtvbName tvbs)
go (DAppT ty1 ty2) = go ty1 `S.union` go ty2
go (DSigT ty ki) = go ty `S.union` fvDType ki
go (DVarT n) = S.singleton n
go (DConT _) = S.empty
go DArrowT = S.empty
go (DLitT {}) = S.empty
go DWildCardT = S.empty
go DStarT = S.empty
dtvbName :: DTyVarBndr -> S.Set Name
dtvbName (DPlainTV n) = S.singleton n
dtvbName (DKindedTV n _) = S.singleton n
-- | Produces 'DLetDec's representing the record selector functions from
-- the provided 'DCon'.
getRecordSelectors :: Quasi q
=> DType -- ^ the type of the argument
-> DCon
-> q [DLetDec]
getRecordSelectors arg_ty (DCon _ _ con_name con _) = case con of
DRecC fields -> go fields
_ -> return []
where
go fields = do
varName <- qNewName "field"
let tvbs = fvDType arg_ty
maybe_forall
| S.null tvbs = id
| otherwise = DForallT (map DPlainTV $ S.toList tvbs) []
num_pats = length fields
return $ concat
[ [ DSigD name (maybe_forall $ DArrowT `DAppT` arg_ty `DAppT` res_ty)
, DFunD name [DClause [DConPa con_name (mk_field_pats n num_pats varName)]
(DVarE varName)] ]
| ((name, _strict, res_ty), n) <- zip fields [0..]
, fvDType res_ty `S.isSubsetOf` tvbs -- exclude "naughty" selectors
]
mk_field_pats :: Int -> Int -> Name -> [DPat]
mk_field_pats 0 total name = DVarPa name : (replicate (total-1) DWildPa)
mk_field_pats n total name = DWildPa : mk_field_pats (n-1) (total-1) name