% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
-Desugaring list comprehensions and array comprehensions
+Desugaring list comprehensions, monad comprehensions and array comprehensions
\begin{code}
-{-# OPTIONS_GHC -w #-}
+{-# LANGUAGE NamedFieldPuns #-}
+{-# OPTIONS -fno-warn-incomplete-patterns #-}
-- The above warning supression flag is a temporary kludge.
-- While working on this module you are encouraged to remove it and fix
-- any warnings in the module. See
--- http://hackage.haskell.org/trac/ghc/wiki/WorkingConventions#Warnings
+-- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
-- for details
-module DsListComp ( dsListComp, dsPArrComp ) where
+module DsListComp ( dsListComp, dsPArrComp, dsMonadComp ) where
#include "HsVersions.h"
-import {-# SOURCE #-} DsExpr ( dsLExpr, dsLocalBinds )
+import {-# SOURCE #-} DsExpr ( dsExpr, dsLExpr, dsLocalBinds )
-import BasicTypes
import HsSyn
import TcHsSyn
import CoreSyn
+import MkCore
import DsMonad -- the monadery used in the desugarer
import DsUtils
import DynFlags
import CoreUtils
-import Var
+import Id
import Type
-import TysPrim
import TysWiredIn
import Match
import PrelNames
-import PrelInfo
import SrcLoc
-import Panic
+import Outputable
+import FastString
+import TcType
\end{code}
List comprehensions may be desugared in one of two ways: ``ordinary''
\begin{code}
dsListComp :: [LStmt Id]
- -> LHsExpr Id
- -> Type -- Type of list elements
+ -> Type -- Type of entire list
-> DsM CoreExpr
-dsListComp lquals body elt_ty
- = getDOptsDs `thenDs` \dflags ->
- let
- quals = map unLoc lquals
- in
- if not (dopt Opt_RewriteRules dflags) || dopt Opt_IgnoreInterfacePragmas dflags
- -- Either rules are switched off, or we are ignoring what there are;
- -- Either way foldr/build won't happen, so use the more efficient
- -- Wadler-style desugaring
- || isParallelComp quals
- -- Foldr-style desugaring can't handle
- -- parallel list comprehensions
- then deListComp quals body (mkNilExpr elt_ty)
-
- else -- Foldr/build should be enabled, so desugar
- -- into foldrs and builds
- newTyVarsDs [alphaTyVar] `thenDs` \ [n_tyvar] ->
- let
- n_ty = mkTyVarTy n_tyvar
- c_ty = mkFunTys [elt_ty, n_ty] n_ty
- in
- newSysLocalsDs [c_ty,n_ty] `thenDs` \ [c, n] ->
- dfListComp c n quals body `thenDs` \ result ->
- dsLookupGlobalId buildName `thenDs` \ build_id ->
- returnDs (Var build_id `App` Type elt_ty
- `App` mkLams [n_tyvar, c, n] result)
-
- where isParallelComp (ParStmt bndrstmtss : _) = True
- isParallelComp _ = False
+dsListComp lquals res_ty = do
+ dflags <- getDOptsDs
+ let quals = map unLoc lquals
+ elt_ty = case tcTyConAppArgs res_ty of
+ [elt_ty] -> elt_ty
+ _ -> pprPanic "dsListComp" (ppr res_ty $$ ppr lquals)
+
+ if not (dopt Opt_EnableRewriteRules dflags) || dopt Opt_IgnoreInterfacePragmas dflags
+ -- Either rules are switched off, or we are ignoring what there are;
+ -- Either way foldr/build won't happen, so use the more efficient
+ -- Wadler-style desugaring
+ || isParallelComp quals
+ -- Foldr-style desugaring can't handle parallel list comprehensions
+ then deListComp quals (mkNilExpr elt_ty)
+ else mkBuildExpr elt_ty (\(c, _) (n, _) -> dfListComp c n quals)
+ -- Foldr/build should be enabled, so desugar
+ -- into foldrs and builds
+
+ where
+ -- We must test for ParStmt anywhere, not just at the head, because an extension
+ -- to list comprehensions would be to add brackets to specify the associativity
+ -- of qualifier lists. This is really easy to do by adding extra ParStmts into the
+ -- mix of possibly a single element in length, so we do this to leave the possibility open
+ isParallelComp = any isParallelStmt
+
+ isParallelStmt (ParStmt _ _ _ _) = True
+ isParallelStmt _ = False
+
+
+-- This function lets you desugar a inner list comprehension and a list of the binders
+-- of that comprehension that we need in the outer comprehension into such an expression
+-- and the type of the elements that it outputs (tuples of binders)
+dsInnerListComp :: ([LStmt Id], [Id]) -> DsM (CoreExpr, Type)
+dsInnerListComp (stmts, bndrs)
+ = do { expr <- dsListComp (stmts ++ [noLoc $ mkLastStmt (mkBigLHsVarTup bndrs)])
+ (mkListTy bndrs_tuple_type)
+ ; return (expr, bndrs_tuple_type) }
+ where
+ bndrs_tuple_type = mkBigCoreVarTupTy bndrs
+
+-- This function factors out commonality between the desugaring strategies for TransformStmt.
+-- Given such a statement it gives you back an expression representing how to compute the transformed
+-- list and the tuple that you need to bind from that list in order to proceed with your desugaring
+dsTransformStmt :: Stmt Id -> DsM (CoreExpr, LPat Id)
+dsTransformStmt (TransformStmt stmts binders usingExpr maybeByExpr _ _)
+ = do { (expr, binders_tuple_type) <- dsInnerListComp (stmts, binders)
+ ; usingExpr' <- dsLExpr usingExpr
+
+ ; using_args <-
+ case maybeByExpr of
+ Nothing -> return [expr]
+ Just byExpr -> do
+ byExpr' <- dsLExpr byExpr
+
+ us <- newUniqueSupply
+ [tuple_binder] <- newSysLocalsDs [binders_tuple_type]
+ let byExprWrapper = mkTupleCase us binders byExpr' tuple_binder (Var tuple_binder)
+
+ return [Lam tuple_binder byExprWrapper, expr]
+
+ ; let inner_list_expr = mkApps usingExpr' ((Type binders_tuple_type) : using_args)
+ pat = mkBigLHsVarPatTup binders
+ ; return (inner_list_expr, pat) }
+
+-- This function factors out commonality between the desugaring strategies for GroupStmt.
+-- Given such a statement it gives you back an expression representing how to compute the transformed
+-- list and the tuple that you need to bind from that list in order to proceed with your desugaring
+dsGroupStmt :: Stmt Id -> DsM (CoreExpr, LPat Id)
+dsGroupStmt (GroupStmt { grpS_stmts = stmts, grpS_bndrs = binderMap
+ , grpS_by = by, grpS_using = using }) = do
+ let (fromBinders, toBinders) = unzip binderMap
+
+ fromBindersTypes = map idType fromBinders
+ toBindersTypes = map idType toBinders
+
+ toBindersTupleType = mkBigCoreTupTy toBindersTypes
+
+ -- Desugar an inner comprehension which outputs a list of tuples of the "from" binders
+ (expr, from_tup_ty) <- dsInnerListComp (stmts, fromBinders)
+
+ -- Work out what arguments should be supplied to that expression: i.e. is an extraction
+ -- function required? If so, create that desugared function and add to arguments
+ usingExpr' <- dsLExpr using
+ usingArgs <- case by of
+ Nothing -> return [expr]
+ Just by_e -> do { by_e' <- dsLExpr by_e
+ ; us <- newUniqueSupply
+ ; [from_tup_id] <- newSysLocalsDs [from_tup_ty]
+ ; let by_wrap = mkTupleCase us fromBinders by_e'
+ from_tup_id (Var from_tup_id)
+ ; return [Lam from_tup_id by_wrap, expr] }
+
+ -- Create an unzip function for the appropriate arity and element types and find "map"
+ (unzip_fn, unzip_rhs) <- mkUnzipBind fromBindersTypes
+ map_id <- dsLookupGlobalId mapName
+
+ -- Generate the expressions to build the grouped list
+ let -- First we apply the grouping function to the inner list
+ inner_list_expr = mkApps usingExpr' ((Type from_tup_ty) : usingArgs)
+ -- Then we map our "unzip" across it to turn the lists of tuples into tuples of lists
+ -- We make sure we instantiate the type variable "a" to be a list of "from" tuples and
+ -- the "b" to be a tuple of "to" lists!
+ unzipped_inner_list_expr = mkApps (Var map_id)
+ [Type (mkListTy from_tup_ty), Type toBindersTupleType, Var unzip_fn, inner_list_expr]
+ -- Then finally we bind the unzip function around that expression
+ bound_unzipped_inner_list_expr = Let (Rec [(unzip_fn, unzip_rhs)]) unzipped_inner_list_expr
+
+ -- Build a pattern that ensures the consumer binds into the NEW binders, which hold lists rather than single values
+ let pat = mkBigLHsVarPatTup toBinders
+ return (bound_unzipped_inner_list_expr, pat)
+
\end{code}
%************************************************************************
with the Unboxed variety.
\begin{code}
-deListComp :: [Stmt Id] -> LHsExpr Id -> CoreExpr -> DsM CoreExpr
-deListComp (ParStmt stmtss_w_bndrs : quals) body list
- = mappM do_list_comp stmtss_w_bndrs `thenDs` \ exps ->
- mkZipBind qual_tys `thenDs` \ (zip_fn, zip_rhs) ->
+deListComp :: [Stmt Id] -> CoreExpr -> DsM CoreExpr
- -- Deal with [e | pat <- zip l1 .. ln] in example above
- deBindComp pat (Let (Rec [(zip_fn, zip_rhs)]) (mkApps (Var zip_fn) exps))
- quals body list
+deListComp [] _ = panic "deListComp"
- where
- bndrs_s = map snd stmtss_w_bndrs
+deListComp (LastStmt body _ : quals) list
+ = -- Figure 7.4, SLPJ, p 135, rule C above
+ ASSERT( null quals )
+ do { core_body <- dsLExpr body
+ ; return (mkConsExpr (exprType core_body) core_body list) }
- -- pat is the pattern ((x1,..,xn), (y1,..,ym)) in the example above
- pat = mkTuplePat pats
- pats = map mk_hs_tuple_pat bndrs_s
+ -- Non-last: must be a guard
+deListComp (ExprStmt guard _ _ _ : quals) list = do -- rule B above
+ core_guard <- dsLExpr guard
+ core_rest <- deListComp quals list
+ return (mkIfThenElse core_guard core_rest list)
+
+-- [e | let B, qs] = let B in [e | qs]
+deListComp (LetStmt binds : quals) list = do
+ core_rest <- deListComp quals list
+ dsLocalBinds binds core_rest
- -- Types of (x1,..,xn), (y1,..,yn) etc
- qual_tys = map mk_bndrs_tys bndrs_s
+deListComp (stmt@(TransformStmt {}) : quals) list = do
+ (inner_list_expr, pat) <- dsTransformStmt stmt
+ deBindComp pat inner_list_expr quals list
- do_list_comp (stmts, bndrs)
- = dsListComp stmts (mk_hs_tuple_expr bndrs)
- (mk_bndrs_tys bndrs)
+deListComp (stmt@(GroupStmt {}) : quals) list = do
+ (inner_list_expr, pat) <- dsGroupStmt stmt
+ deBindComp pat inner_list_expr quals list
- mk_bndrs_tys bndrs = mkCoreTupTy (map idType bndrs)
+deListComp (BindStmt pat list1 _ _ : quals) core_list2 = do -- rule A' above
+ core_list1 <- dsLExpr list1
+ deBindComp pat core_list1 quals core_list2
- -- Last: the one to return
-deListComp [] body list -- Figure 7.4, SLPJ, p 135, rule C above
- = dsLExpr body `thenDs` \ core_body ->
- returnDs (mkConsExpr (exprType core_body) core_body list)
+deListComp (ParStmt stmtss_w_bndrs _ _ _ : quals) list
+ = do
+ exps_and_qual_tys <- mapM dsInnerListComp stmtss_w_bndrs
+ let (exps, qual_tys) = unzip exps_and_qual_tys
+
+ (zip_fn, zip_rhs) <- mkZipBind qual_tys
- -- Non-last: must be a guard
-deListComp (ExprStmt guard _ _ : quals) body list -- rule B above
- = dsLExpr guard `thenDs` \ core_guard ->
- deListComp quals body list `thenDs` \ core_rest ->
- returnDs (mkIfThenElse core_guard core_rest list)
+ -- Deal with [e | pat <- zip l1 .. ln] in example above
+ deBindComp pat (Let (Rec [(zip_fn, zip_rhs)]) (mkApps (Var zip_fn) exps))
+ quals list
--- [e | let B, qs] = let B in [e | qs]
-deListComp (LetStmt binds : quals) body list
- = deListComp quals body list `thenDs` \ core_rest ->
- dsLocalBinds binds core_rest
+ where
+ bndrs_s = map snd stmtss_w_bndrs
-deListComp (BindStmt pat list1 _ _ : quals) body core_list2 -- rule A' above
- = dsLExpr list1 `thenDs` \ core_list1 ->
- deBindComp pat core_list1 quals body core_list2
+ -- pat is the pattern ((x1,..,xn), (y1,..,ym)) in the example above
+ pat = mkBigLHsPatTup pats
+ pats = map mkBigLHsVarPatTup bndrs_s
\end{code}
\begin{code}
-deBindComp pat core_list1 quals body core_list2
- = let
- u3_ty@u1_ty = exprType core_list1 -- two names, same thing
+deBindComp :: OutPat Id
+ -> CoreExpr
+ -> [Stmt Id]
+ -> CoreExpr
+ -> DsM (Expr Id)
+deBindComp pat core_list1 quals core_list2 = do
+ let
+ u3_ty@u1_ty = exprType core_list1 -- two names, same thing
- -- u1_ty is a [alpha] type, and u2_ty = alpha
- u2_ty = hsLPatType pat
+ -- u1_ty is a [alpha] type, and u2_ty = alpha
+ u2_ty = hsLPatType pat
- res_ty = exprType core_list2
- h_ty = u1_ty `mkFunTy` res_ty
- in
- newSysLocalsDs [h_ty, u1_ty, u2_ty, u3_ty] `thenDs` \ [h, u1, u2, u3] ->
+ res_ty = exprType core_list2
+ h_ty = u1_ty `mkFunTy` res_ty
+
+ [h, u1, u2, u3] <- newSysLocalsDs [h_ty, u1_ty, u2_ty, u3_ty]
-- the "fail" value ...
let
- core_fail = App (Var h) (Var u3)
- letrec_body = App (Var h) core_list1
- in
- deListComp quals body core_fail `thenDs` \ rest_expr ->
- matchSimply (Var u2) (StmtCtxt ListComp) pat
- rest_expr core_fail `thenDs` \ core_match ->
+ core_fail = App (Var h) (Var u3)
+ letrec_body = App (Var h) core_list1
+
+ rest_expr <- deListComp quals core_fail
+ core_match <- matchSimply (Var u2) (StmtCtxt ListComp) pat rest_expr core_fail
+
let
- rhs = Lam u1 $
+ rhs = Lam u1 $
Case (Var u1) u1 res_ty
[(DataAlt nilDataCon, [], core_list2),
(DataAlt consDataCon, [u2, u3], core_match)]
-- Increasing order of tag
- in
- returnDs (Let (Rec [(h, rhs)]) letrec_body)
-\end{code}
-
-
-\begin{code}
-mkZipBind :: [Type] -> DsM (Id, CoreExpr)
--- mkZipBind [t1, t2]
--- = (zip, \as1:[t1] as2:[t2]
--- -> case as1 of
--- [] -> []
--- (a1:as'1) -> case as2 of
--- [] -> []
--- (a2:as'2) -> (a2,a2) : zip as'1 as'2)]
-
-mkZipBind elt_tys
- = mappM newSysLocalDs list_tys `thenDs` \ ass ->
- mappM newSysLocalDs elt_tys `thenDs` \ as' ->
- mappM newSysLocalDs list_tys `thenDs` \ as's ->
- newSysLocalDs zip_fn_ty `thenDs` \ zip_fn ->
- let
- inner_rhs = mkConsExpr ret_elt_ty
- (mkCoreTup (map Var as'))
- (mkVarApps (Var zip_fn) as's)
- zip_body = foldr mk_case inner_rhs (zip3 ass as' as's)
- in
- returnDs (zip_fn, mkLams ass zip_body)
- where
- list_tys = map mkListTy elt_tys
- ret_elt_ty = mkCoreTupTy elt_tys
- list_ret_ty = mkListTy ret_elt_ty
- zip_fn_ty = mkFunTys list_tys list_ret_ty
-
- mk_case (as, a', as') rest
- = Case (Var as) as list_ret_ty
- [(DataAlt nilDataCon, [], mkNilExpr ret_elt_ty),
- (DataAlt consDataCon, [a', as'], rest)]
- -- Increasing order of tag
--- Helper functions that makes an HsTuple only for non-1-sized tuples
-mk_hs_tuple_expr :: [Id] -> LHsExpr Id
-mk_hs_tuple_expr [] = nlHsVar unitDataConId
-mk_hs_tuple_expr [id] = nlHsVar id
-mk_hs_tuple_expr ids = noLoc $ ExplicitTuple [ nlHsVar i | i <- ids ] Boxed
-
-mk_hs_tuple_pat :: [Id] -> LPat Id
-mk_hs_tuple_pat bs = mkTuplePat (map nlVarPat bs)
+
+ return (Let (Rec [(h, rhs)]) letrec_body)
\end{code}
-
%************************************************************************
%* *
\subsection[DsListComp-foldr-build]{Foldr/Build desugaring of list comprehensions}
\end{verbatim}
\begin{code}
-dfListComp :: Id -> Id -- 'c' and 'n'
- -> [Stmt Id] -- the rest of the qual's
- -> LHsExpr Id
- -> DsM CoreExpr
+dfListComp :: Id -> Id -- 'c' and 'n'
+ -> [Stmt Id] -- the rest of the qual's
+ -> DsM CoreExpr
+
+dfListComp _ _ [] = panic "dfListComp"
- -- Last: the one to return
-dfListComp c_id n_id [] body
- = dsLExpr body `thenDs` \ core_body ->
- returnDs (mkApps (Var c_id) [core_body, Var n_id])
+dfListComp c_id n_id (LastStmt body _ : quals)
+ = ASSERT( null quals )
+ do { core_body <- dsLExpr body
+ ; return (mkApps (Var c_id) [core_body, Var n_id]) }
-- Non-last: must be a guard
-dfListComp c_id n_id (ExprStmt guard _ _ : quals) body
- = dsLExpr guard `thenDs` \ core_guard ->
- dfListComp c_id n_id quals body `thenDs` \ core_rest ->
- returnDs (mkIfThenElse core_guard core_rest (Var n_id))
-
-dfListComp c_id n_id (LetStmt binds : quals) body
- -- new in 1.3, local bindings
- = dfListComp c_id n_id quals body `thenDs` \ core_rest ->
+dfListComp c_id n_id (ExprStmt guard _ _ _ : quals) = do
+ core_guard <- dsLExpr guard
+ core_rest <- dfListComp c_id n_id quals
+ return (mkIfThenElse core_guard core_rest (Var n_id))
+
+dfListComp c_id n_id (LetStmt binds : quals) = do
+ -- new in 1.3, local bindings
+ core_rest <- dfListComp c_id n_id quals
dsLocalBinds binds core_rest
-dfListComp c_id n_id (BindStmt pat list1 _ _ : quals) body
+dfListComp c_id n_id (stmt@(TransformStmt {}) : quals) = do
+ (inner_list_expr, pat) <- dsTransformStmt stmt
+ -- Anyway, we bind the newly transformed list via the generic binding function
+ dfBindComp c_id n_id (pat, inner_list_expr) quals
+
+dfListComp c_id n_id (stmt@(GroupStmt {}) : quals) = do
+ (inner_list_expr, pat) <- dsGroupStmt stmt
+ -- Anyway, we bind the newly grouped list via the generic binding function
+ dfBindComp c_id n_id (pat, inner_list_expr) quals
+
+dfListComp c_id n_id (BindStmt pat list1 _ _ : quals) = do
-- evaluate the two lists
- = dsLExpr list1 `thenDs` \ core_list1 ->
-
+ core_list1 <- dsLExpr list1
+
+ -- Do the rest of the work in the generic binding builder
+ dfBindComp c_id n_id (pat, core_list1) quals
+
+dfBindComp :: Id -> Id -- 'c' and 'n'
+ -> (LPat Id, CoreExpr)
+ -> [Stmt Id] -- the rest of the qual's
+ -> DsM CoreExpr
+dfBindComp c_id n_id (pat, core_list1) quals = do
-- find the required type
let x_ty = hsLPatType pat
- b_ty = idType n_id
- in
+ b_ty = idType n_id
-- create some new local id's
- newSysLocalsDs [b_ty,x_ty] `thenDs` \ [b,x] ->
+ [b, x] <- newSysLocalsDs [b_ty, x_ty]
-- build rest of the comprehesion
- dfListComp c_id b quals body `thenDs` \ core_rest ->
+ core_rest <- dfListComp c_id b quals
-- build the pattern match
- matchSimply (Var x) (StmtCtxt ListComp)
- pat core_rest (Var b) `thenDs` \ core_expr ->
+ core_expr <- matchSimply (Var x) (StmtCtxt ListComp)
+ pat core_rest (Var b)
-- now build the outermost foldr, and return
- dsLookupGlobalId foldrName `thenDs` \ foldr_id ->
- returnDs (
- Var foldr_id `App` Type x_ty
- `App` Type b_ty
- `App` mkLams [x, b] core_expr
- `App` Var n_id
- `App` core_list1
- )
+ mkFoldrExpr x_ty b_ty (mkLams [x, b] core_expr) (Var n_id) core_list1
+\end{code}
+
+%************************************************************************
+%* *
+\subsection[DsFunGeneration]{Generation of zip/unzip functions for use in desugaring}
+%* *
+%************************************************************************
+
+\begin{code}
+
+mkZipBind :: [Type] -> DsM (Id, CoreExpr)
+-- mkZipBind [t1, t2]
+-- = (zip, \as1:[t1] as2:[t2]
+-- -> case as1 of
+-- [] -> []
+-- (a1:as'1) -> case as2 of
+-- [] -> []
+-- (a2:as'2) -> (a1, a2) : zip as'1 as'2)]
+
+mkZipBind elt_tys = do
+ ass <- mapM newSysLocalDs elt_list_tys
+ as' <- mapM newSysLocalDs elt_tys
+ as's <- mapM newSysLocalDs elt_list_tys
+
+ zip_fn <- newSysLocalDs zip_fn_ty
+
+ let inner_rhs = mkConsExpr elt_tuple_ty
+ (mkBigCoreVarTup as')
+ (mkVarApps (Var zip_fn) as's)
+ zip_body = foldr mk_case inner_rhs (zip3 ass as' as's)
+
+ return (zip_fn, mkLams ass zip_body)
+ where
+ elt_list_tys = map mkListTy elt_tys
+ elt_tuple_ty = mkBigCoreTupTy elt_tys
+ elt_tuple_list_ty = mkListTy elt_tuple_ty
+
+ zip_fn_ty = mkFunTys elt_list_tys elt_tuple_list_ty
+
+ mk_case (as, a', as') rest
+ = Case (Var as) as elt_tuple_list_ty
+ [(DataAlt nilDataCon, [], mkNilExpr elt_tuple_ty),
+ (DataAlt consDataCon, [a', as'], rest)]
+ -- Increasing order of tag
+
+
+mkUnzipBind :: [Type] -> DsM (Id, CoreExpr)
+-- mkUnzipBind [t1, t2]
+-- = (unzip, \ys :: [(t1, t2)] -> foldr (\ax :: (t1, t2) axs :: ([t1], [t2])
+-- -> case ax of
+-- (x1, x2) -> case axs of
+-- (xs1, xs2) -> (x1 : xs1, x2 : xs2))
+-- ([], [])
+-- ys)
+--
+-- We use foldr here in all cases, even if rules are turned off, because we may as well!
+mkUnzipBind elt_tys = do
+ ax <- newSysLocalDs elt_tuple_ty
+ axs <- newSysLocalDs elt_list_tuple_ty
+ ys <- newSysLocalDs elt_tuple_list_ty
+ xs <- mapM newSysLocalDs elt_tys
+ xss <- mapM newSysLocalDs elt_list_tys
+
+ unzip_fn <- newSysLocalDs unzip_fn_ty
+
+ [us1, us2] <- sequence [newUniqueSupply, newUniqueSupply]
+
+ let nil_tuple = mkBigCoreTup (map mkNilExpr elt_tys)
+
+ concat_expressions = map mkConcatExpression (zip3 elt_tys (map Var xs) (map Var xss))
+ tupled_concat_expression = mkBigCoreTup concat_expressions
+
+ folder_body_inner_case = mkTupleCase us1 xss tupled_concat_expression axs (Var axs)
+ folder_body_outer_case = mkTupleCase us2 xs folder_body_inner_case ax (Var ax)
+ folder_body = mkLams [ax, axs] folder_body_outer_case
+
+ unzip_body <- mkFoldrExpr elt_tuple_ty elt_list_tuple_ty folder_body nil_tuple (Var ys)
+ return (unzip_fn, mkLams [ys] unzip_body)
+ where
+ elt_tuple_ty = mkBigCoreTupTy elt_tys
+ elt_tuple_list_ty = mkListTy elt_tuple_ty
+ elt_list_tys = map mkListTy elt_tys
+ elt_list_tuple_ty = mkBigCoreTupTy elt_list_tys
+
+ unzip_fn_ty = elt_tuple_list_ty `mkFunTy` elt_list_tuple_ty
+
+ mkConcatExpression (list_element_ty, head, tail) = mkConsExpr list_element_ty head tail
\end{code}
%************************************************************************
--
-- [:e | qss:] = <<[:e | qss:]>> () [:():]
--
-dsPArrComp :: [Stmt Id]
- -> LHsExpr Id
- -> Type -- Don't use; called with `undefined' below
- -> DsM CoreExpr
-dsPArrComp [ParStmt qss] body _ = -- parallel comprehension
- dePArrParComp qss body
-dsPArrComp qs body _ = -- no ParStmt in `qs'
- dsLookupGlobalId replicatePName `thenDs` \repP ->
- let unitArray = mkApps (Var repP) [Type unitTy,
- mkIntExpr 1,
- mkCoreTup []]
- in
- dePArrComp qs body (mkTuplePat []) unitArray
+dsPArrComp :: [Stmt Id]
+ -> DsM CoreExpr
+
+-- Special case for parallel comprehension
+dsPArrComp (ParStmt qss _ _ _ : quals) = dePArrParComp qss quals
+
+-- Special case for simple generators:
+--
+-- <<[:e' | p <- e, qs:]>> = <<[: e' | qs :]>> p e
+--
+-- if matching again p cannot fail, or else
+--
+-- <<[:e' | p <- e, qs:]>> =
+-- <<[:e' | qs:]>> p (filterP (\x -> case x of {p -> True; _ -> False}) e)
+--
+dsPArrComp (BindStmt p e _ _ : qs) = do
+ filterP <- dsLookupDPHId filterPName
+ ce <- dsLExpr e
+ let ety'ce = parrElemType ce
+ false = Var falseDataConId
+ true = Var trueDataConId
+ v <- newSysLocalDs ety'ce
+ pred <- matchSimply (Var v) (StmtCtxt PArrComp) p true false
+ let gen | isIrrefutableHsPat p = ce
+ | otherwise = mkApps (Var filterP) [Type ety'ce, mkLams [v] pred, ce]
+ dePArrComp qs p gen
+
+dsPArrComp qs = do -- no ParStmt in `qs'
+ sglP <- dsLookupDPHId singletonPName
+ let unitArray = mkApps (Var sglP) [Type unitTy, mkCoreTup []]
+ dePArrComp qs (noLoc $ WildPat unitTy) unitArray
-- the work horse
--
dePArrComp :: [Stmt Id]
- -> LHsExpr Id
-> LPat Id -- the current generator pattern
-> CoreExpr -- the current generator expression
-> DsM CoreExpr
+
+dePArrComp [] _ _ = panic "dePArrComp"
+
--
-- <<[:e' | :]>> pa ea = mapP (\pa -> e') ea
--
-dePArrComp [] e' pa cea =
- dsLookupGlobalId mapPName `thenDs` \mapP ->
- let ty = parrElemType cea
- in
- deLambda ty pa e' `thenDs` \(clam,
- ty'e') ->
- returnDs $ mkApps (Var mapP) [Type ty, Type ty'e', clam, cea]
+dePArrComp (LastStmt e' _ : quals) pa cea
+ = ASSERT( null quals )
+ do { mapP <- dsLookupDPHId mapPName
+ ; let ty = parrElemType cea
+ ; (clam, ty'e') <- deLambda ty pa e'
+ ; return $ mkApps (Var mapP) [Type ty, Type ty'e', clam, cea] }
--
-- <<[:e' | b, qs:]>> pa ea = <<[:e' | qs:]>> pa (filterP (\pa -> b) ea)
--
-dePArrComp (ExprStmt b _ _ : qs) body pa cea =
- dsLookupGlobalId filterPName `thenDs` \filterP ->
- let ty = parrElemType cea
- in
- deLambda ty pa b `thenDs` \(clam,_) ->
- dePArrComp qs body pa (mkApps (Var filterP) [Type ty, clam, cea])
+dePArrComp (ExprStmt b _ _ _ : qs) pa cea = do
+ filterP <- dsLookupDPHId filterPName
+ let ty = parrElemType cea
+ (clam,_) <- deLambda ty pa b
+ dePArrComp qs pa (mkApps (Var filterP) [Type ty, clam, cea])
+
+--
+-- <<[:e' | p <- e, qs:]>> pa ea =
+-- let ef = \pa -> e
+-- in
+-- <<[:e' | qs:]>> (pa, p) (crossMap ea ef)
+--
+-- if matching again p cannot fail, or else
--
-- <<[:e' | p <- e, qs:]>> pa ea =
-- let ef = \pa -> filterP (\x -> case x of {p -> True; _ -> False}) e
-- in
-- <<[:e' | qs:]>> (pa, p) (crossMapP ea ef)
--
-dePArrComp (BindStmt p e _ _ : qs) body pa cea =
- dsLookupGlobalId filterPName `thenDs` \filterP ->
- dsLookupGlobalId crossMapPName `thenDs` \crossMapP ->
- dsLExpr e `thenDs` \ce ->
- let ety'cea = parrElemType cea
- ety'ce = parrElemType ce
- false = Var falseDataConId
- true = Var trueDataConId
- in
- newSysLocalDs ety'ce `thenDs` \v ->
- matchSimply (Var v) (StmtCtxt PArrComp) p true false `thenDs` \pred ->
- let cef = mkApps (Var filterP) [Type ety'ce, mkLams [v] pred, ce]
- in
- mkLambda ety'cea pa cef `thenDs` \(clam,
- _ ) ->
- let ety'cef = ety'ce -- filter doesn't change the element type
- pa' = mkTuplePat [pa, p]
- in
- dePArrComp qs body pa' (mkApps (Var crossMapP)
- [Type ety'cea, Type ety'cef, cea, clam])
+dePArrComp (BindStmt p e _ _ : qs) pa cea = do
+ filterP <- dsLookupDPHId filterPName
+ crossMapP <- dsLookupDPHId crossMapPName
+ ce <- dsLExpr e
+ let ety'cea = parrElemType cea
+ ety'ce = parrElemType ce
+ false = Var falseDataConId
+ true = Var trueDataConId
+ v <- newSysLocalDs ety'ce
+ pred <- matchSimply (Var v) (StmtCtxt PArrComp) p true false
+ let cef | isIrrefutableHsPat p = ce
+ | otherwise = mkApps (Var filterP) [Type ety'ce, mkLams [v] pred, ce]
+ (clam, _) <- mkLambda ety'cea pa cef
+ let ety'cef = ety'ce -- filter doesn't change the element type
+ pa' = mkLHsPatTup [pa, p]
+
+ dePArrComp qs pa' (mkApps (Var crossMapP)
+ [Type ety'cea, Type ety'cef, cea, clam])
--
-- <<[:e' | let ds, qs:]>> pa ea =
-- <<[:e' | qs:]>> (pa, (x_1, ..., x_n))
-- where
-- {x_1, ..., x_n} = DV (ds) -- Defined Variables
--
-dePArrComp (LetStmt ds : qs) body pa cea =
- dsLookupGlobalId mapPName `thenDs` \mapP ->
- let xs = map unLoc (collectLocalBinders ds)
- ty'cea = parrElemType cea
- in
- newSysLocalDs ty'cea `thenDs` \v ->
- dsLocalBinds ds (mkCoreTup (map Var xs)) `thenDs` \clet ->
- newSysLocalDs (exprType clet) `thenDs` \let'v ->
- let projBody = mkDsLet (NonRec let'v clet) $
- mkCoreTup [Var v, Var let'v]
- errTy = exprType projBody
- errMsg = "DsListComp.dePArrComp: internal error!"
- in
- mkErrorAppDs pAT_ERROR_ID errTy errMsg `thenDs` \cerr ->
- matchSimply (Var v) (StmtCtxt PArrComp) pa projBody cerr`thenDs` \ccase ->
- let pa' = mkTuplePat [pa, mkTuplePat (map nlVarPat xs)]
- proj = mkLams [v] ccase
- in
- dePArrComp qs body pa' (mkApps (Var mapP)
- [Type ty'cea, Type errTy, proj, cea])
+dePArrComp (LetStmt ds : qs) pa cea = do
+ mapP <- dsLookupDPHId mapPName
+ let xs = collectLocalBinders ds
+ ty'cea = parrElemType cea
+ v <- newSysLocalDs ty'cea
+ clet <- dsLocalBinds ds (mkCoreTup (map Var xs))
+ let'v <- newSysLocalDs (exprType clet)
+ let projBody = mkCoreLet (NonRec let'v clet) $
+ mkCoreTup [Var v, Var let'v]
+ errTy = exprType projBody
+ errMsg = ptext (sLit "DsListComp.dePArrComp: internal error!")
+ cerr <- mkErrorAppDs pAT_ERROR_ID errTy errMsg
+ ccase <- matchSimply (Var v) (StmtCtxt PArrComp) pa projBody cerr
+ let pa' = mkLHsPatTup [pa, mkLHsPatTup (map nlVarPat xs)]
+ proj = mkLams [v] ccase
+ dePArrComp qs pa' (mkApps (Var mapP)
+ [Type ty'cea, Type errTy, proj, cea])
--
-- The parser guarantees that parallel comprehensions can only appear as
-- singeltons qualifier lists, which we already special case in the caller.
-- So, encountering one here is a bug.
--
-dePArrComp (ParStmt _ : _) _ _ _ =
+dePArrComp (ParStmt _ _ _ _ : _) _ _ =
panic "DsListComp.dePArrComp: malformed comprehension AST"
-- <<[:e' | qs | qss:]>> pa ea =
-- where
-- {x_1, ..., x_n} = DV (qs)
--
-dePArrParComp qss body =
- deParStmt qss `thenDs` \(pQss,
- ceQss) ->
- dePArrComp [] body pQss ceQss
+dePArrParComp :: [([LStmt Id], [Id])] -> [Stmt Id] -> DsM CoreExpr
+dePArrParComp qss quals = do
+ (pQss, ceQss) <- deParStmt qss
+ dePArrComp quals pQss ceQss
where
deParStmt [] =
-- empty parallel statement lists have no source representation
panic "DsListComp.dePArrComp: Empty parallel list comprehension"
- deParStmt ((qs, xs):qss) = -- first statement
- let res_expr = mkExplicitTuple (map nlHsVar xs)
- in
- dsPArrComp (map unLoc qs) res_expr undefined `thenDs` \cqs ->
- parStmts qss (mkTuplePat (map nlVarPat xs)) cqs
+ deParStmt ((qs, xs):qss) = do -- first statement
+ let res_expr = mkLHsVarTuple xs
+ cqs <- dsPArrComp (map unLoc qs ++ [mkLastStmt res_expr])
+ parStmts qss (mkLHsVarPatTup xs) cqs
---
parStmts [] pa cea = return (pa, cea)
- parStmts ((qs, xs):qss) pa cea = -- subsequent statements (zip'ed)
- dsLookupGlobalId zipPName `thenDs` \zipP ->
- let pa' = mkTuplePat [pa, mkTuplePat (map nlVarPat xs)]
- ty'cea = parrElemType cea
- res_expr = mkExplicitTuple (map nlHsVar xs)
- in
- dsPArrComp (map unLoc qs) res_expr undefined `thenDs` \cqs ->
+ parStmts ((qs, xs):qss) pa cea = do -- subsequent statements (zip'ed)
+ zipP <- dsLookupDPHId zipPName
+ let pa' = mkLHsPatTup [pa, mkLHsVarPatTup xs]
+ ty'cea = parrElemType cea
+ res_expr = mkLHsVarTuple xs
+ cqs <- dsPArrComp (map unLoc qs ++ [mkLastStmt res_expr])
let ty'cqs = parrElemType cqs
- cea' = mkApps (Var zipP) [Type ty'cea, Type ty'cqs, cea, cqs]
- in
+ cea' = mkApps (Var zipP) [Type ty'cea, Type ty'cqs, cea, cqs]
parStmts qss pa' cea'
-- generate Core corresponding to `\p -> e'
-> LHsExpr Id -- body
-> DsM (CoreExpr, Type)
deLambda ty p e =
- dsLExpr e `thenDs` \ce ->
- mkLambda ty p ce
+ mkLambda ty p =<< dsLExpr e
-- generate Core for a lambda pattern match, where the body is already in Core
--
-> LPat Id -- argument pattern
-> CoreExpr -- desugared body
-> DsM (CoreExpr, Type)
-mkLambda ty p ce =
- newSysLocalDs ty `thenDs` \v ->
- let errMsg = "DsListComp.deLambda: internal error!"
- ce'ty = exprType ce
- in
- mkErrorAppDs pAT_ERROR_ID ce'ty errMsg `thenDs` \cerr ->
- matchSimply (Var v) (StmtCtxt PArrComp) p ce cerr `thenDs` \res ->
- returnDs (mkLams [v] res, ce'ty)
+mkLambda ty p ce = do
+ v <- newSysLocalDs ty
+ let errMsg = ptext (sLit "DsListComp.deLambda: internal error!")
+ ce'ty = exprType ce
+ cerr <- mkErrorAppDs pAT_ERROR_ID ce'ty errMsg
+ res <- matchSimply (Var v) (StmtCtxt PArrComp) p ce cerr
+ return (mkLams [v] res, ce'ty)
-- obtain the element type of the parallel array produced by the given Core
-- expression
Just (tycon, [ty]) | tycon == parrTyCon -> ty
_ -> panic
"DsListComp.parrElemType: not a parallel array type"
+\end{code}
+
+Translation for monad comprehensions
--- Smart constructor for source tuple patterns
+\begin{code}
+-- Entry point for monad comprehension desugaring
+dsMonadComp :: [LStmt Id] -> DsM CoreExpr
+dsMonadComp stmts = dsMcStmts stmts
+
+dsMcStmts :: [LStmt Id] -> DsM CoreExpr
+dsMcStmts [] = panic "dsMcStmts"
+dsMcStmts (L loc stmt : lstmts) = putSrcSpanDs loc (dsMcStmt stmt lstmts)
+
+---------------
+dsMcStmt :: Stmt Id -> [LStmt Id] -> DsM CoreExpr
+
+dsMcStmt (LastStmt body ret_op) stmts
+ = ASSERT( null stmts )
+ do { body' <- dsLExpr body
+ ; ret_op' <- dsExpr ret_op
+ ; return (App ret_op' body') }
+
+-- [ .. | let binds, stmts ]
+dsMcStmt (LetStmt binds) stmts
+ = do { rest <- dsMcStmts stmts
+ ; dsLocalBinds binds rest }
+
+-- [ .. | a <- m, stmts ]
+dsMcStmt (BindStmt pat rhs bind_op fail_op) stmts
+ = do { rhs' <- dsLExpr rhs
+ ; dsMcBindStmt pat rhs' bind_op fail_op stmts }
+
+-- Apply `guard` to the `exp` expression
+--
+-- [ .. | exp, stmts ]
+--
+dsMcStmt (ExprStmt exp then_exp guard_exp _) stmts
+ = do { exp' <- dsLExpr exp
+ ; guard_exp' <- dsExpr guard_exp
+ ; then_exp' <- dsExpr then_exp
+ ; rest <- dsMcStmts stmts
+ ; return $ mkApps then_exp' [ mkApps guard_exp' [exp']
+ , rest ] }
+
+-- Transform statements desugar like this:
+--
+-- [ .. | qs, then f by e ] -> f (\q_v -> e) [| qs |]
+--
+-- where [| qs |] is the desugared inner monad comprehenion generated by the
+-- statements `qs`.
+dsMcStmt (TransformStmt stmts binders usingExpr maybeByExpr return_op bind_op) stmts_rest
+ = do { expr <- dsInnerMonadComp stmts binders return_op
+ ; let binders_tup_type = mkBigCoreTupTy $ map idType binders
+ ; usingExpr' <- dsLExpr usingExpr
+ ; using_args <- case maybeByExpr of
+ Nothing -> return [expr]
+ Just byExpr -> do
+ byExpr' <- dsLExpr byExpr
+ us <- newUniqueSupply
+ tup_binder <- newSysLocalDs binders_tup_type
+ let byExprWrapper = mkTupleCase us binders byExpr' tup_binder (Var tup_binder)
+ return [Lam tup_binder byExprWrapper, expr]
+
+ ; let pat = mkBigLHsVarPatTup binders
+ rhs = mkApps usingExpr' ((Type binders_tup_type) : using_args)
+
+ ; dsMcBindStmt pat rhs bind_op noSyntaxExpr stmts_rest }
+
+-- Group statements desugar like this:
--
-mkTuplePat :: [LPat Id] -> LPat Id
-mkTuplePat [lpat] = lpat
-mkTuplePat lpats = noLoc $ mkVanillaTuplePat lpats Boxed
+-- [| (q, then group by e using f); rest |]
+-- ---> f {qt} (\qv -> e) [| q; return qv |] >>= \ n_tup ->
+-- case unzip n_tup of qv' -> [| rest |]
+--
+-- where variables (v1:t1, ..., vk:tk) are bound by q
+-- qv = (v1, ..., vk)
+-- qt = (t1, ..., tk)
+-- (>>=) :: m2 a -> (a -> m3 b) -> m3 b
+-- f :: forall a. (a -> t) -> m1 a -> m2 (n a)
+-- n_tup :: n qt
+-- unzip :: n qt -> (n t1, ..., n tk) (needs Functor n)
+
+dsMcStmt (GroupStmt { grpS_stmts = stmts, grpS_bndrs = bndrs
+ , grpS_by = by, grpS_using = using
+ , grpS_ret = return_op, grpS_bind = bind_op
+ , grpS_fmap = fmap_op }) stmts_rest
+ = do { let (from_bndrs, to_bndrs) = unzip bndrs
+ from_bndr_tys = map idType from_bndrs -- Types ty
+
+ -- Desugar an inner comprehension which outputs a list of tuples of the "from" binders
+ ; expr <- dsInnerMonadComp stmts from_bndrs return_op
+
+ -- Work out what arguments should be supplied to that expression: i.e. is an extraction
+ -- function required? If so, create that desugared function and add to arguments
+ ; usingExpr' <- dsLExpr using
+ ; usingArgs <- case by of
+ Nothing -> return [expr]
+ Just by_e -> do { by_e' <- dsLExpr by_e
+ ; lam <- matchTuple from_bndrs by_e'
+ ; return [lam, expr] }
+
+ -- Generate the expressions to build the grouped list
+ -- Build a pattern that ensures the consumer binds into the NEW binders,
+ -- which hold monads rather than single values
+ ; fmap_op' <- dsExpr fmap_op
+ ; bind_op' <- dsExpr bind_op
+ ; let bind_ty = exprType bind_op' -- m2 (n (a,b,c)) -> (n (a,b,c) -> r1) -> r2
+ n_tup_ty = funArgTy $ funArgTy $ funResultTy bind_ty -- n (a,b,c)
+ tup_n_ty = mkBigCoreVarTupTy to_bndrs
+
+ ; body <- dsMcStmts stmts_rest
+ ; n_tup_var <- newSysLocalDs n_tup_ty
+ ; tup_n_var <- newSysLocalDs tup_n_ty
+ ; tup_n_expr <- mkMcUnzipM fmap_op' n_tup_var from_bndr_tys
+ ; us <- newUniqueSupply
+ ; let rhs' = mkApps usingExpr' usingArgs
+ body' = mkTupleCase us to_bndrs body tup_n_var tup_n_expr
+
+ ; return (mkApps bind_op' [rhs', Lam n_tup_var body']) }
+
+-- Parallel statements. Use `Control.Monad.Zip.mzip` to zip parallel
+-- statements, for example:
+--
+-- [ body | qs1 | qs2 | qs3 ]
+-- -> [ body | (bndrs1, (bndrs2, bndrs3))
+-- <- [bndrs1 | qs1] `mzip` ([bndrs2 | qs2] `mzip` [bndrs3 | qs3]) ]
+--
+-- where `mzip` has type
+-- mzip :: forall a b. m a -> m b -> m (a,b)
+-- NB: we need a polymorphic mzip because we call it several times
+
+dsMcStmt (ParStmt pairs mzip_op bind_op return_op) stmts_rest
+ = do { exps_w_tys <- mapM ds_inner pairs -- Pairs (exp :: m ty, ty)
+ ; mzip_op' <- dsExpr mzip_op
+
+ ; let -- The pattern variables
+ pats = map (mkBigLHsVarPatTup . snd) pairs
+ -- Pattern with tuples of variables
+ -- [v1,v2,v3] => (v1, (v2, v3))
+ pat = foldr1 (\p1 p2 -> mkLHsPatTup [p1, p2]) pats
+ (rhs, _) = foldr1 (\(e1,t1) (e2,t2) ->
+ (mkApps mzip_op' [Type t1, Type t2, e1, e2],
+ mkBoxedTupleTy [t1,t2]))
+ exps_w_tys
+
+ ; dsMcBindStmt pat rhs bind_op noSyntaxExpr stmts_rest }
+ where
+ ds_inner (stmts, bndrs) = do { exp <- dsInnerMonadComp stmts bndrs mono_ret_op
+ ; return (exp, tup_ty) }
+ where
+ mono_ret_op = HsWrap (WpTyApp tup_ty) return_op
+ tup_ty = mkBigCoreVarTupTy bndrs
+
+dsMcStmt stmt _ = pprPanic "dsMcStmt: unexpected stmt" (ppr stmt)
+
+
+matchTuple :: [Id] -> CoreExpr -> DsM CoreExpr
+-- (matchTuple [a,b,c] body)
+-- returns the Core term
+-- \x. case x of (a,b,c) -> body
+matchTuple ids body
+ = do { us <- newUniqueSupply
+ ; tup_id <- newSysLocalDs (mkBigCoreVarTupTy ids)
+ ; return (Lam tup_id $ mkTupleCase us ids body tup_id (Var tup_id)) }
+
+-- general `rhs' >>= \pat -> stmts` desugaring where `rhs'` is already a
+-- desugared `CoreExpr`
+dsMcBindStmt :: LPat Id
+ -> CoreExpr -- ^ the desugared rhs of the bind statement
+ -> SyntaxExpr Id
+ -> SyntaxExpr Id
+ -> [LStmt Id]
+ -> DsM CoreExpr
+dsMcBindStmt pat rhs' bind_op fail_op stmts
+ = do { body <- dsMcStmts stmts
+ ; bind_op' <- dsExpr bind_op
+ ; var <- selectSimpleMatchVarL pat
+ ; let bind_ty = exprType bind_op' -- rhs -> (pat -> res1) -> res2
+ res1_ty = funResultTy (funArgTy (funResultTy bind_ty))
+ ; match <- matchSinglePat (Var var) (StmtCtxt DoExpr) pat
+ res1_ty (cantFailMatchResult body)
+ ; match_code <- handle_failure pat match fail_op
+ ; return (mkApps bind_op' [rhs', Lam var match_code]) }
--- Smart constructor for source tuple expressions
+ where
+ -- In a monad comprehension expression, pattern-match failure just calls
+ -- the monadic `fail` rather than throwing an exception
+ handle_failure pat match fail_op
+ | matchCanFail match
+ = do { fail_op' <- dsExpr fail_op
+ ; fail_msg <- mkStringExpr (mk_fail_msg pat)
+ ; extractMatchResult match (App fail_op' fail_msg) }
+ | otherwise
+ = extractMatchResult match (error "It can't fail")
+
+ mk_fail_msg :: Located e -> String
+ mk_fail_msg pat = "Pattern match failure in monad comprehension at " ++
+ showSDoc (ppr (getLoc pat))
+
+-- Desugar nested monad comprehensions, for example in `then..` constructs
+-- dsInnerMonadComp quals [a,b,c] ret_op
+-- returns the desugaring of
+-- [ (a,b,c) | quals ]
+
+dsInnerMonadComp :: [LStmt Id]
+ -> [Id] -- Return a tuple of these variables
+ -> HsExpr Id -- The monomorphic "return" operator
+ -> DsM CoreExpr
+dsInnerMonadComp stmts bndrs ret_op
+ = dsMcStmts (stmts ++ [noLoc (LastStmt (mkBigLHsVarTup bndrs) ret_op)])
+
+-- The `unzip` function for `GroupStmt` in a monad comprehensions
+--
+-- unzip :: m (a,b,..) -> (m a,m b,..)
+-- unzip m_tuple = ( liftM selN1 m_tuple
+-- , liftM selN2 m_tuple
+-- , .. )
--
-mkExplicitTuple :: [LHsExpr id] -> LHsExpr id
-mkExplicitTuple [lexp] = lexp
-mkExplicitTuple lexps = noLoc $ ExplicitTuple lexps Boxed
+-- mkMcUnzipM fmap ys [t1, t2]
+-- = ( fmap (selN1 :: (t1, t2) -> t1) ys
+-- , fmap (selN2 :: (t1, t2) -> t2) ys )
+
+mkMcUnzipM :: CoreExpr -- fmap
+ -> Id -- Of type n (a,b,c)
+ -> [Type] -- [a,b,c]
+ -> DsM CoreExpr -- Of type (n a, n b, n c)
+mkMcUnzipM fmap_op ys elt_tys
+ = do { xs <- mapM newSysLocalDs elt_tys
+ ; tup_xs <- newSysLocalDs (mkBigCoreTupTy elt_tys)
+
+ ; let arg_ty = idType ys
+ mk_elt i = mkApps fmap_op -- fmap :: forall a b. (a -> b) -> n a -> n b
+ [ Type arg_ty, Type (elt_tys !! i)
+ , mk_sel i, Var ys]
+
+ mk_sel n = Lam tup_xs $
+ mkTupleSelector xs (xs !! n) tup_xs (Var tup_xs)
+
+ ; return (mkBigCoreTup (map mk_elt [0..length elt_tys - 1])) }
\end{code}
projects / ghc-hetmet.git / blobdiff