% (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}
-module DsListComp ( dsListComp, dsPArrComp ) where
+{-# 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/Commentary/CodingStyle#Warnings
+-- for details
+
+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 StaticFlags
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''
-> LHsExpr Id
-> Type -- Type of list elements
-> DsM CoreExpr
-dsListComp lquals body elt_ty
- = getDOptsDs `thenDs` \dflags ->
- let
- quals = map unLoc lquals
- in
- if opt_RulesOff || 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 body elt_ty = do
+ dflags <- getDOptsDs
+ let quals = map unLoc 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 body (mkNilExpr elt_ty)
+ else mkBuildExpr elt_ty (\(c, _) (n, _) -> dfListComp c n quals body)
+ -- 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 (mkBigLHsVarTup bndrs) bndrs_tuple_type
+ return (expr, bndrs_tuple_type)
+ where
+ bndrs_types = map idType bndrs
+ bndrs_tuple_type = mkBigCoreTupTy bndrs_types
+
+
+-- 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 stmts binderMap by 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 (either id noLoc 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 (ParStmt stmtss_w_bndrs _ _ _ : quals) body 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
-- Deal with [e | pat <- zip l1 .. ln] in example above
deBindComp pat (Let (Rec [(zip_fn, zip_rhs)]) (mkApps (Var zip_fn) exps))
bndrs_s = map snd stmtss_w_bndrs
-- pat is the pattern ((x1,..,xn), (y1,..,ym)) in the example above
- pat = mkTuplePat pats
- pats = map mk_hs_tuple_pat bndrs_s
-
- -- Types of (x1,..,xn), (y1,..,yn) etc
- qual_tys = map mk_bndrs_tys bndrs_s
-
- do_list_comp (stmts, bndrs)
- = dsListComp stmts (mk_hs_tuple_expr bndrs)
- (mk_bndrs_tys bndrs)
-
- mk_bndrs_tys bndrs = mkCoreTupTy (map idType bndrs)
+ pat = mkBigLHsPatTup pats
+ pats = map mkBigLHsVarPatTup bndrs_s
-- 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 [] body list = do -- Figure 7.4, SLPJ, p 135, rule C above
+ core_body <- dsLExpr body
+ return (mkConsExpr (exprType core_body) core_body list)
-- 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)
+deListComp (ExprStmt guard _ _ _ : quals) body list = do -- rule B above
+ core_guard <- dsLExpr guard
+ core_rest <- deListComp quals body list
+ return (mkIfThenElse core_guard core_rest list)
-- [e | let B, qs] = let B in [e | qs]
-deListComp (LetStmt binds : quals) body list
- = deListComp quals body list `thenDs` \ core_rest ->
+deListComp (LetStmt binds : quals) body list = do
+ core_rest <- deListComp quals body list
dsLocalBinds binds core_rest
-deListComp (BindStmt pat list1 _ _ : quals) body core_list2 -- rule A' above
- = dsLExpr list1 `thenDs` \ core_list1 ->
+deListComp (stmt@(TransformStmt {}) : quals) body list = do
+ (inner_list_expr, pat) <- dsTransformStmt stmt
+ deBindComp pat inner_list_expr quals body list
+
+deListComp (stmt@(GroupStmt {}) : quals) body list = do
+ (inner_list_expr, pat) <- dsGroupStmt stmt
+ deBindComp pat inner_list_expr quals body list
+
+deListComp (BindStmt pat list1 _ _ : quals) body core_list2 = do -- rule A' above
+ core_list1 <- dsLExpr list1
deBindComp pat core_list1 quals body core_list2
\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]
+ -> LHsExpr Id
+ -> CoreExpr
+ -> DsM (Expr Id)
+deBindComp pat core_list1 quals body 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 body 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)
+
+ return (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)
-\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
+ -> LHsExpr Id
+ -> DsM CoreExpr
-- 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 [] body = 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) body = do
+ core_guard <- dsLExpr guard
+ core_rest <- dfListComp c_id n_id quals body
+ return (mkIfThenElse core_guard core_rest (Var n_id))
+
+dfListComp c_id n_id (LetStmt binds : quals) body = do
+ -- new in 1.3, local bindings
+ core_rest <- dfListComp c_id n_id quals body
dsLocalBinds binds core_rest
-dfListComp c_id n_id (BindStmt pat list1 _ _ : quals) body
+dfListComp c_id n_id (stmt@(TransformStmt {}) : quals) body = 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 body
+
+dfListComp c_id n_id (stmt@(GroupStmt {}) : quals) body = 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 body
+
+dfListComp c_id n_id (BindStmt pat list1 _ _ : quals) body = 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 body
+
+dfBindComp :: Id -> Id -- 'c' and 'n'
+ -> (LPat Id, CoreExpr)
+ -> [Stmt Id] -- the rest of the qual's
+ -> LHsExpr Id
+ -> DsM CoreExpr
+dfBindComp c_id n_id (pat, core_list1) quals body = 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 body
-- 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 qs body _ =
- dsLookupGlobalId replicatePName `thenDs` \repP ->
- let unitArray = mkApps (Var repP) [Type unitTy,
- mkIntExpr 1,
- mkCoreTup []]
- in
- dePArrComp qs body (mkTuplePat []) unitArray
+dsPArrComp :: [Stmt Id]
+ -> LHsExpr Id
+ -> Type -- Don't use; called with `undefined' below
+ -> DsM CoreExpr
+dsPArrComp [ParStmt qss _ _ _] body _ = -- parallel comprehension
+ dePArrParComp qss body
+
+-- 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) body _ = 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 body p gen
+
+dsPArrComp qs body _ = do -- no ParStmt in `qs'
+ sglP <- dsLookupDPHId singletonPName
+ let unitArray = mkApps (Var sglP) [Type unitTy, mkCoreTup []]
+ dePArrComp qs body (noLoc $ WildPat unitTy) unitArray
+
+
-- the work horse
--
--
-- <<[: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 [] e' pa cea = 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) body pa cea = do
+ filterP <- dsLookupDPHId filterPName
+ let ty = parrElemType cea
+ (clam,_) <- deLambda ty pa b
+ dePArrComp qs body 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 = filterP (\x -> case x of {p -> True; _ -> False}) e
+-- let ef = \pa -> filterP (\x -> case x of {p -> True; _ -> False}) e
-- in
--- <<[:e' | qs:]>> (pa, p) (crossP ea ef)
---
-dePArrComp (BindStmt p e _ _ : qs) body pa cea =
- dsLookupGlobalId filterPName `thenDs` \filterP ->
- dsLookupGlobalId crossPName `thenDs` \crossP ->
- dsLExpr e `thenDs` \ce ->
- let ty'cea = parrElemType cea
- ty'ce = parrElemType ce
- false = Var falseDataConId
- true = Var trueDataConId
- in
- newSysLocalDs ty'ce `thenDs` \v ->
- matchSimply (Var v) (StmtCtxt PArrComp) p true false `thenDs` \pred ->
- let cef = mkApps (Var filterP) [Type ty'ce, mkLams [v] pred, ce]
- ty'cef = ty'ce -- filterP preserves the type
- pa' = mkTuplePat [pa, p]
- in
- dePArrComp qs body pa' (mkApps (Var crossP) [Type ty'cea, Type ty'cef, cea, cef])
+-- <<[:e' | qs:]>> (pa, p) (crossMapP ea ef)
+--
+dePArrComp (BindStmt p e _ _ : qs) body 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 body 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))
--- (mapP (\v@pa -> (v, let ds in (x_1, ..., x_n))) ea)
+-- (mapP (\v@pa -> let ds in (v, (x_1, ..., x_n))) ea)
-- 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, proj, cea])
+dePArrComp (LetStmt ds : qs) body 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 body 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 _ _ _ _ : _) _ _ _ =
+ panic "DsListComp.dePArrComp: malformed comprehension AST"
+
-- <<[:e' | qs | qss:]>> pa ea =
-- <<[:e' | qss:]>> (pa, (x_1, ..., x_n))
-- (zipP ea <<[:(x_1, ..., x_n) | qs:]>>)
-- where
-- {x_1, ..., x_n} = DV (qs)
--
-dePArrComp (ParStmt qss : qs) body pa cea =
- dsLookupGlobalId crossPName `thenDs` \crossP ->
- deParStmt qss `thenDs` \(pQss,
- ceQss) ->
- let ty'cea = parrElemType cea
- ty'ceQss = parrElemType ceQss
- pa' = mkTuplePat [pa, pQss]
- in
- dePArrComp qs body pa' (mkApps (Var crossP) [Type ty'cea, Type ty'ceQss,
- cea, ceQss])
+dePArrParComp :: [([LStmt Id], [Id])] -> LHsExpr Id -> DsM CoreExpr
+dePArrParComp qss body = do
+ (pQss, ceQss) <- deParStmt qss
+ dePArrComp [] body pQss ceQss
where
deParStmt [] =
- -- empty parallel statement lists have not source representation
+ -- 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) res_expr undefined
+ 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) res_expr undefined
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'
--
-deLambda :: Type -- type of the argument
- -> LPat Id -- argument pattern
- -> LHsExpr Id -- body
- -> DsM (CoreExpr, Type)
-deLambda ty p e =
- newSysLocalDs ty `thenDs` \v ->
- dsLExpr e `thenDs` \ce ->
- let errTy = exprType ce
- errMsg = "DsListComp.deLambda: internal error!"
- in
- mkErrorAppDs pAT_ERROR_ID errTy errMsg `thenDs` \cerr ->
- matchSimply (Var v) (StmtCtxt PArrComp) p ce cerr `thenDs` \res ->
- returnDs (mkLams [v] res, errTy)
+deLambda :: Type -- type of the argument
+ -> LPat Id -- argument pattern
+ -> LHsExpr Id -- body
+ -> DsM (CoreExpr, Type)
+deLambda ty p e =
+ mkLambda ty p =<< dsLExpr e
+
+-- generate Core for a lambda pattern match, where the body is already in Core
+--
+mkLambda :: Type -- type of the argument
+ -> LPat Id -- argument pattern
+ -> CoreExpr -- desugared body
+ -> DsM (CoreExpr, Type)
+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
+
+\begin{code}
+
+-- | Keep the "context" of a monad comprehension in a small data type to avoid
+-- some boilerplate...
+data DsMonadComp = DsMonadComp
+ { mc_return :: Either (SyntaxExpr Id) (Expr CoreBndr)
+ , mc_body :: LHsExpr Id
+ , mc_m_ty :: Type
+ }
+
+--
+-- Entry point for monad comprehension desugaring
+--
+dsMonadComp :: [LStmt Id] -- the statements
+ -> SyntaxExpr Id -- the "return" function
+ -> LHsExpr Id -- the body
+ -> Type -- the final type
+ -> DsM CoreExpr
+dsMonadComp stmts return_op body res_ty
+ = dsMcStmts stmts (DsMonadComp (Left return_op) body m_ty)
+ where
+ (m_ty, _) = tcSplitAppTy res_ty
+
+
+dsMcStmts :: [LStmt Id]
+ -> DsMonadComp
+ -> DsM CoreExpr
+
+-- No statements left for desugaring. Desugar the body after calling "return"
+-- on it.
+dsMcStmts [] DsMonadComp { mc_return, mc_body }
+ = case mc_return of
+ Left ret -> dsLExpr $ noLoc ret `nlHsApp` mc_body
+ Right ret' -> do
+ { body' <- dsLExpr mc_body
+ ; return $ mkApps ret' [body'] }
+
+-- Otherwise desugar each statement step by step
+dsMcStmts ((L loc stmt) : lstmts) mc
+ = putSrcSpanDs loc (dsMcStmt stmt lstmts mc)
+
+
+dsMcStmt :: Stmt Id
+ -> [LStmt Id]
+ -> DsMonadComp
+ -> DsM CoreExpr
--- Smart constructor for source tuple patterns
+-- [ .. | let binds, stmts ]
+dsMcStmt (LetStmt binds) stmts mc
+ = do { rest <- dsMcStmts stmts mc
+ ; dsLocalBinds binds rest }
+
+-- [ .. | a <- m, stmts ]
+dsMcStmt (BindStmt pat rhs bind_op fail_op) stmts mc
+ = do { rhs' <- dsLExpr rhs
+ ; dsMcBindStmt pat rhs' bind_op fail_op stmts mc }
+
+-- Apply `guard` to the `exp` expression
+--
+-- [ .. | exp, stmts ]
+--
+dsMcStmt (ExprStmt exp then_exp guard_exp _) stmts mc
+ = do { exp' <- dsLExpr exp
+ ; guard_exp' <- dsExpr guard_exp
+ ; then_exp' <- dsExpr then_exp
+ ; rest <- dsMcStmts stmts mc
+ ; 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 mc
+ = do { (expr, _) <- dsInnerMonadComp (stmts, binders) (mc { mc_return = Left return_op })
+ ; let binders_tuple_type = mkBigCoreTupTy $ map idType binders
+ ; usingExpr' <- dsLExpr usingExpr
+ ; using_args <- case maybeByExpr of
+ Nothing -> return [expr]
+ Just byExpr -> do
+ byExpr' <- dsLExpr byExpr
+ us <- newUniqueSupply
+ tuple_binder <- newSysLocalDs binders_tuple_type
+ let byExprWrapper = mkTupleCase us binders byExpr' tuple_binder (Var tuple_binder)
+ return [Lam tuple_binder byExprWrapper, expr]
+
+ ; let pat = mkBigLHsVarPatTup binders
+ rhs = mkApps usingExpr' ((Type binders_tuple_type) : using_args)
+
+ ; dsMcBindStmt pat rhs bind_op noSyntaxExpr stmts_rest mc }
+
+-- Group statements desugar like this:
+--
+-- [| q, then group by e using f |] -> (f (\q_v -> e) [| q |]) >>= (return . (unzip q_v))
--
-mkTuplePat :: [LPat Id] -> LPat Id
-mkTuplePat [lpat] = lpat
-mkTuplePat lpats = noLoc $ mkVanillaTuplePat lpats Boxed
+-- which is equal to
+--
+-- [| q, then group by e using f |] -> liftM (unzip q_v) (f (\q_v -> e) [| q |])
+--
+-- where unzip is of the form
+--
+-- unzip :: m (a,b,c,..) -> (m a,m b,m c,..)
+-- unzip m_tuple = ( liftM selN1 m_tuple
+-- , liftM selN2 m_tuple
+-- , .. )
+-- where selN1 (a,b,c,..) = a
+-- selN2 (a,b,c,..) = b
+-- ..
+--
+dsMcStmt (GroupStmt stmts binderMap by using return_op bind_op liftM_op) stmts_rest mc
+ = do { let (fromBinders, toBinders) = unzip binderMap
+ fromBindersTypes = map idType fromBinders
+ fromBindersTupleTy = mkBigCoreTupTy fromBindersTypes
+ toBindersTypes = map idType toBinders
+ toBindersTupleTy = mkBigCoreTupTy toBindersTypes
+ m_ty = mc_m_ty mc
+
+ -- Desugar an inner comprehension which outputs a list of tuples of the "from" binders
+ ; (expr, _) <- dsInnerMonadComp (stmts, fromBinders) (mc { mc_return = Left 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 (either id noLoc using)
+ ; usingArgs <- case by of
+ Nothing -> return [expr]
+ Just by_e -> do { by_e' <- dsLExpr by_e
+ ; us <- newUniqueSupply
+ ; from_tup_id <- newSysLocalDs fromBindersTupleTy
+ ; 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
+ ; liftM_op' <- dsExpr liftM_op
+ ; (unzip_fn, unzip_rhs) <- mkMcUnzipM liftM_op' m_ty fromBindersTypes
+
+ -- Generate the expressions to build the grouped list
+
+ ; let -- First we apply the grouping function to the inner monad
+ inner_monad_expr = mkApps usingExpr' ((Type fromBindersTupleTy) : usingArgs)
+ -- Then we map our "unzip" across it to turn the "monad of tuples" into "tuples of monads"
+ -- We make sure we instantiate the type variable "a" to be a "monad of 'from' tuples" and
+ -- the "b" to be a "tuple of 'to' monads"!
+ unzipped_inner_monad_expr = mkApps liftM_op' -- !
+ -- Types:
+ [ Type (m_ty `mkAppTy` fromBindersTupleTy), Type toBindersTupleTy
+ -- And arguments:
+ , Var unzip_fn, inner_monad_expr ]
+ -- Then finally we bind the unzip function around that expression
+ bound_unzipped_inner_monad_expr = Let (Rec [(unzip_fn, unzip_rhs)]) unzipped_inner_monad_expr
+
+ -- Build a pattern that ensures the consumer binds into the NEW binders, which hold monads
+ -- rather than single values
+ ; let pat = mkBigLHsVarPatTup toBinders
+ rhs = bound_unzipped_inner_monad_expr
+
+ ; dsMcBindStmt pat rhs bind_op noSyntaxExpr stmts_rest mc }
+
+-- Parallel statements. Use `Control.Monad.Zip.mzip` to zip parallel
+-- statements, for example:
+--
+-- [ body | qs1 | qs2 | qs3 ]
+-- -> [ body | (bndrs1, (bndrs2, bndrs3)) <- mzip qs1 (mzip qs2 qs3) ]
+--
+-- where `mzip` is of the form
+--
+-- mzip :: m a -> m b -> m (a,b)
+--
+dsMcStmt (ParStmt pairs mzip_op bind_op return_op) stmts_rest mc
+ = do { -- Get types for `return`
+ return_op' <- dsExpr return_op
+ ; let pairs_with_return = map (\tp@(_,b) -> (mkReturn b,tp)) pairs
+ mkReturn bndrs = mkApps return_op' [Type (mkBigCoreTupTy (map idType bndrs))]
+
+ ; pairs' <- mapM (\(r,tp) -> dsInnerMonadComp tp mc{mc_return = Right r})
+ pairs_with_return
+
+ ; let (exps, _qual_tys) = unzip pairs'
+ -- Types of our `Id`s are getting messed up by `dsInnerMonadComp`
+ -- so we construct them by hand:
+ qual_tys = map (mkBigCoreTupTy . map idType . snd) pairs
+
+ ; mzip_op' <- dsExpr mzip_op
+ ; (zip_fn, zip_rhs) <- mkMcZipM mzip_op' (mc_m_ty mc) qual_tys
+
+ ; let -- The pattern variables
+ vars = map (mkBigLHsVarPatTup . snd) pairs
+ -- Pattern with tuples of variables
+ -- [v1,v2,v3] => (v1, (v2, v3))
+ pat = foldr (\tn tm -> mkBigLHsPatTup [tn, tm]) (last vars) (init vars)
+ rhs = Let (Rec [(zip_fn, zip_rhs)]) (mkApps (Var zip_fn) exps)
+
+ ; dsMcBindStmt pat rhs bind_op noSyntaxExpr stmts_rest mc }
+
+dsMcStmt stmt _ _ = pprPanic "dsMcStmt: unexpected stmt" (ppr stmt)
+
+
+-- 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]
+ -> DsMonadComp
+ -> DsM CoreExpr
+dsMcBindStmt pat rhs' bind_op fail_op stmts mc
+ = do { body <- dsMcStmts stmts mc
+ ; 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 :: ([LStmt Id], [Id])
+ -> DsMonadComp
+ -> DsM (CoreExpr, Type)
+dsInnerMonadComp (stmts, bndrs) DsMonadComp{ mc_return, mc_m_ty }
+ = do { expr <- dsMcStmts stmts mc'
+ ; return (expr, bndrs_tuple_type) }
+ where
+ bndrs_types = map idType bndrs
+ bndrs_tuple_type = mkAppTy mc_m_ty $ mkBigCoreTupTy bndrs_types
+ mc' = DsMonadComp mc_return (mkBigLHsVarTup bndrs) mc_m_ty
+
+-- 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
+-- , .. )
+--
+-- mkMcUnzipM m [t1, t2]
+-- = (unzip_fn, \ys :: m (t1, t2) ->
+-- ( liftM (selN1 :: (t1, t2) -> t1) ys
+-- , liftM (selN2 :: (t1, t2) -> t2) ys
+-- ))
+--
+mkMcUnzipM :: CoreExpr
+ -> Type -- m
+ -> [Type] -- [a,b,c,..]
+ -> DsM (Id, CoreExpr)
+mkMcUnzipM liftM_op m_ty elt_tys
+ = do { ys <- newSysLocalDs monad_tuple_ty
+ ; xs <- mapM newSysLocalDs elt_tys
+ ; scrut <- newSysLocalDs tuple_tys
+
+ ; unzip_fn <- newSysLocalDs unzip_fn_ty
+
+ ; let -- Select one Id from our tuple
+ selectExpr n = mkLams [scrut] $ mkTupleSelector xs (xs !! n) scrut (Var scrut)
+ -- Apply 'selectVar' and 'ys' to 'liftM'
+ tupleElem n = mkApps liftM_op
+ -- Types (m is figured out by the type checker):
+ -- liftM :: forall a b. (a -> b) -> m a -> m b
+ [ Type tuple_tys, Type (elt_tys !! n)
+ -- Arguments:
+ , selectExpr n, Var ys ]
+ -- The final expression with the big tuple
+ unzip_body = mkBigCoreTup [ tupleElem n | n <- [0..length elt_tys - 1] ]
+
+ ; return (unzip_fn, mkLams [ys] unzip_body) }
+ where monad_tys = map (m_ty `mkAppTy`) elt_tys -- [m a,m b,m c,..]
+ tuple_monad_tys = mkBigCoreTupTy monad_tys -- (m a,m b,m c,..)
+ tuple_tys = mkBigCoreTupTy elt_tys -- (a,b,c,..)
+ monad_tuple_ty = m_ty `mkAppTy` tuple_tys -- m (a,b,c,..)
+ unzip_fn_ty = monad_tuple_ty `mkFunTy` tuple_monad_tys -- m (a,b,c,..) -> (m a,m b,m c,..)
+
+-- Generate the `mzip` function for `ParStmt` in monad comprehensions, for
+-- example:
--
-mkExplicitTuple :: [LHsExpr id] -> LHsExpr id
-mkExplicitTuple [lexp] = lexp
-mkExplicitTuple lexps = noLoc $ ExplicitTuple lexps Boxed
+-- mzip :: m t1
+-- -> (m t2 -> m t3 -> m (t2, t3))
+-- -> m (t1, (t2, t3))
+--
+-- mkMcZipM m [t1, t2, t3]
+-- = (zip_fn, \(q1::t1) (q2::t2) (q3::t3) ->
+-- mzip q1 (mzip q2 q3))
+--
+mkMcZipM :: CoreExpr
+ -> Type
+ -> [Type]
+ -> DsM (Id, CoreExpr)
+
+mkMcZipM mzip_op m_ty tys@(_:_:_) -- min. 2 types
+ = do { (ids, t1, tuple_ty, zip_body) <- loop tys
+ ; zip_fn <- newSysLocalDs $
+ (m_ty `mkAppTy` t1)
+ `mkFunTy`
+ (m_ty `mkAppTy` tuple_ty)
+ `mkFunTy`
+ (m_ty `mkAppTy` mkBigCoreTupTy [t1, tuple_ty])
+ ; return (zip_fn, mkLams ids zip_body) }
+
+ where
+ -- loop :: [Type] -> DsM ([Id], Type, [Type], CoreExpr)
+ loop [t1, t2] = do -- last run of the `loop`
+ { ids@[a,b] <- newSysLocalsDs (map (m_ty `mkAppTy`) [t1,t2])
+ ; let zip_body = mkApps mzip_op [ Type t1, Type t2 , Var a, Var b ]
+ ; return (ids, t1, t2, zip_body) }
+
+ loop (t1:tr) = do
+ { -- Get ty, ids etc from the "inner" zip
+ (ids', t1', t2', zip_body') <- loop tr
+
+ ; a <- newSysLocalDs $ m_ty `mkAppTy` t1
+ ; let tuple_ty' = mkBigCoreTupTy [t1', t2']
+ zip_body = mkApps mzip_op [ Type t1, Type tuple_ty', Var a, zip_body' ]
+ ; return ((a:ids'), t1, tuple_ty', zip_body) }
+
+-- This case should never happen:
+mkMcZipM _ _ tys = pprPanic "mkMcZipM: unexpected argument" (ppr tys)
+
\end{code}
projects / ghc-hetmet.git / blobdiff