2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[HsExpr]{Abstract Haskell syntax: expressions}
9 #include "HsVersions.h"
12 import HsDecls ( HsGroup )
14 import HsLit ( HsLit(..), HsOverLit )
15 import HsTypes ( LHsType, PostTcType )
16 import HsImpExp ( isOperator, pprHsVar )
17 import HsBinds ( HsLocalBinds, DictBinds, ExprCoFn, isEmptyLocalBinds )
20 import Type ( Type, pprParendType )
21 import Var ( TyVar, Id )
23 import BasicTypes ( IPName, Boxity, tupleParens, Arity, Fixity(..) )
24 import SrcLoc ( Located(..), unLoc )
30 %************************************************************************
32 \subsection{Expressions proper}
34 %************************************************************************
37 type LHsExpr id = Located (HsExpr id)
39 -------------------------
40 -- PostTcExpr is an evidence expression attached to the
41 -- syntax tree by the type checker (c.f. postTcType)
42 -- We use a PostTcTable where there are a bunch of pieces of
43 -- evidence, more than is convenient to keep individually
44 type PostTcExpr = HsExpr Id
45 type PostTcTable = [(Name, Id)]
47 noPostTcExpr :: PostTcExpr
48 noPostTcExpr = HsLit (HsString FSLIT("noPostTcExpr"))
50 noPostTcTable :: PostTcTable
53 -------------------------
54 -- SyntaxExpr is like PostTcExpr, but it's filled in a little earlier,
55 -- by the renamer. It's used for rebindable syntax.
56 -- E.g. (>>=) is filled in before the renamer by the appropriate Name
57 -- for (>>=), and then instantiated by the type checker with its
60 type SyntaxExpr id = HsExpr id
62 noSyntaxExpr :: SyntaxExpr id -- Before renaming, and sometimes after,
63 -- (if the syntax slot makes no sense)
64 noSyntaxExpr = HsLit (HsString FSLIT("noSyntaxExpr"))
67 type SyntaxTable id = [(Name, SyntaxExpr id)]
68 -- *** Currently used only for CmdTop (sigh) ***
69 -- * Before the renamer, this list is noSyntaxTable
71 -- * After the renamer, it takes the form [(std_name, HsVar actual_name)]
72 -- For example, for the 'return' op of a monad
73 -- normal case: (GHC.Base.return, HsVar GHC.Base.return)
74 -- with rebindable syntax: (GHC.Base.return, return_22)
75 -- where return_22 is whatever "return" is in scope
77 -- * After the type checker, it takes the form [(std_name, <expression>)]
78 -- where <expression> is the evidence for the method
80 noSyntaxTable :: SyntaxTable id
84 -------------------------
86 = HsVar id -- variable
87 | HsIPVar (IPName id) -- implicit parameter
88 | HsOverLit (HsOverLit id) -- Overloaded literals
89 | HsLit HsLit -- Simple (non-overloaded) literals
91 | HsLam (MatchGroup id) -- Currently always a single match
93 | HsApp (LHsExpr id) -- Application
96 -- Operator applications:
97 -- NB Bracketed ops such as (+) come out as Vars.
99 -- NB We need an expr for the operator in an OpApp/Section since
100 -- the typechecker may need to apply the operator to a few types.
102 | OpApp (LHsExpr id) -- left operand
103 (LHsExpr id) -- operator
104 Fixity -- Renamer adds fixity; bottom until then
105 (LHsExpr id) -- right operand
107 | NegApp (LHsExpr id) -- negated expr
108 (SyntaxExpr id) -- Name of 'negate'
110 | HsPar (LHsExpr id) -- parenthesised expr
112 | SectionL (LHsExpr id) -- operand
113 (LHsExpr id) -- operator
114 | SectionR (LHsExpr id) -- operator
115 (LHsExpr id) -- operand
117 | HsCase (LHsExpr id)
120 | HsIf (LHsExpr id) -- predicate
121 (LHsExpr id) -- then part
122 (LHsExpr id) -- else part
124 | HsLet (HsLocalBinds id) -- let(rec)
127 | HsDo (HsStmtContext Name) -- The parameterisation is unimportant
128 -- because in this context we never use
129 -- the PatGuard or ParStmt variant
130 [LStmt id] -- "do":one or more stmts
131 (LHsExpr id) -- The body; the last expression in the 'do'
132 -- of [ body | ... ] in a list comp
133 PostTcType -- Type of the whole expression
135 | ExplicitList -- syntactic list
136 PostTcType -- Gives type of components of list
139 | ExplicitPArr -- syntactic parallel array: [:e1, ..., en:]
140 PostTcType -- type of elements of the parallel array
143 | ExplicitTuple -- tuple
145 -- NB: Unit is ExplicitTuple []
146 -- for tuples, we can get the types
147 -- direct from the components
151 -- Record construction
152 | RecordCon (Located id) -- The constructor. After type checking
153 -- it's the dataConWrapId of the constructor
154 PostTcExpr -- Data con Id applied to type args
158 | RecordUpd (LHsExpr id)
160 PostTcType -- Type of *input* record
161 PostTcType -- Type of *result* record (may differ from
162 -- type of input record)
164 | ExprWithTySig -- e :: type
168 | ExprWithTySigOut -- TRANSLATION
170 (LHsType Name) -- Retain the signature for round-tripping purposes
172 | ArithSeq -- arithmetic sequence
176 | PArrSeq -- arith. sequence for parallel array
177 PostTcExpr -- [:e1..e2:] or [:e1, e2..e3:]
180 | HsSCC FastString -- "set cost centre" (_scc_) annotation
181 (LHsExpr id) -- expr whose cost is to be measured
183 | HsCoreAnn FastString -- hdaume: core annotation
186 -----------------------------------------------------------
187 -- MetaHaskell Extensions
188 | HsBracket (HsBracket id)
190 | HsBracketOut (HsBracket Name) -- Output of the type checker is the *original*
191 [PendingSplice] -- renamed expression, plus *typechecked* splices
192 -- to be pasted back in by the desugarer
194 | HsSpliceE (HsSplice id)
196 -----------------------------------------------------------
197 -- Arrow notation extension
199 | HsProc (LPat id) -- arrow abstraction, proc
200 (LHsCmdTop id) -- body of the abstraction
201 -- always has an empty stack
203 ---------------------------------------
204 -- The following are commands, not expressions proper
206 | HsArrApp -- Arrow tail, or arrow application (f -< arg)
207 (LHsExpr id) -- arrow expression, f
208 (LHsExpr id) -- input expression, arg
209 PostTcType -- type of the arrow expressions f,
210 -- of the form a t t', where arg :: t
211 HsArrAppType -- higher-order (-<<) or first-order (-<)
212 Bool -- True => right-to-left (f -< arg)
213 -- False => left-to-right (arg >- f)
215 | HsArrForm -- Command formation, (| e cmd1 .. cmdn |)
216 (LHsExpr id) -- the operator
217 -- after type-checking, a type abstraction to be
218 -- applied to the type of the local environment tuple
219 (Maybe Fixity) -- fixity (filled in by the renamer), for forms that
220 -- were converted from OpApp's by the renamer
221 [LHsCmdTop id] -- argument commands
225 These constructors only appear temporarily in the parser.
226 The renamer translates them into the Right Thing.
229 | EWildPat -- wildcard
231 | EAsPat (Located id) -- as pattern
234 | ELazyPat (LHsExpr id) -- ~ pattern
236 | HsType (LHsType id) -- Explicit type argument; e.g f {| Int |} x y
239 Everything from here on appears only in typechecker output.
242 | TyLam -- TRANSLATION
245 | TyApp -- TRANSLATION
246 (LHsExpr id) -- generated by Spec
249 -- DictLam and DictApp are "inverses"
257 | HsCoerce ExprCoFn -- TRANSLATION
260 type PendingSplice = (Name, LHsExpr Id) -- Typechecked splices, waiting to be
261 -- pasted back in by the desugarer
264 A @Dictionary@, unless of length 0 or 1, becomes a tuple. A
265 @ClassDictLam dictvars methods expr@ is, therefore:
267 \ x -> case x of ( dictvars-and-methods-tuple ) -> expr
271 instance OutputableBndr id => Outputable (HsExpr id) where
272 ppr expr = pprExpr expr
276 pprExpr :: OutputableBndr id => HsExpr id -> SDoc
278 pprExpr e = pprDeeper (ppr_expr e)
280 pprBinds :: OutputableBndr id => HsLocalBinds id -> SDoc
281 pprBinds b = pprDeeper (ppr b)
283 ppr_lexpr :: OutputableBndr id => LHsExpr id -> SDoc
284 ppr_lexpr e = ppr_expr (unLoc e)
286 ppr_expr (HsVar v) = pprHsVar v
287 ppr_expr (HsIPVar v) = ppr v
288 ppr_expr (HsLit lit) = ppr lit
289 ppr_expr (HsOverLit lit) = ppr lit
290 ppr_expr (HsPar e) = parens (ppr_lexpr e)
292 ppr_expr (HsCoreAnn s e)
293 = vcat [ptext SLIT("HsCoreAnn") <+> ftext s, ppr_lexpr e]
295 ppr_expr (HsApp e1 e2)
296 = let (fun, args) = collect_args e1 [e2] in
297 hang (ppr_lexpr fun) 2 (sep (map pprParendExpr args))
299 collect_args (L _ (HsApp fun arg)) args = collect_args fun (arg:args)
300 collect_args fun args = (fun, args)
302 ppr_expr (OpApp e1 op fixity e2)
304 HsVar v -> pp_infixly v
307 pp_e1 = pprParendExpr e1 -- Add parens to make precedence clear
308 pp_e2 = pprParendExpr e2
311 = hang (ppr op) 2 (sep [pp_e1, pp_e2])
314 = sep [nest 2 pp_e1, pprInfix v, nest 2 pp_e2]
316 ppr_expr (NegApp e _) = char '-' <+> pprParendExpr e
318 ppr_expr (SectionL expr op)
320 HsVar v -> pp_infixly v
323 pp_expr = pprParendExpr expr
325 pp_prefixly = hang (hsep [text " \\ x_ ->", ppr op])
326 4 (hsep [pp_expr, ptext SLIT("x_ )")])
327 pp_infixly v = parens (sep [pp_expr, pprInfix v])
329 ppr_expr (SectionR op expr)
331 HsVar v -> pp_infixly v
334 pp_expr = pprParendExpr expr
336 pp_prefixly = hang (hsep [text "( \\ x_ ->", ppr op, ptext SLIT("x_")])
337 4 ((<>) pp_expr rparen)
339 = parens (sep [pprInfix v, pp_expr])
341 ppr_expr (HsLam matches)
342 = pprMatches LambdaExpr matches
344 ppr_expr (HsCase expr matches)
345 = sep [ sep [ptext SLIT("case"), nest 4 (ppr expr), ptext SLIT("of")],
346 nest 2 (pprMatches CaseAlt matches) ]
348 ppr_expr (HsIf e1 e2 e3)
349 = sep [hsep [ptext SLIT("if"), nest 2 (ppr e1), ptext SLIT("then")],
354 -- special case: let ... in let ...
355 ppr_expr (HsLet binds expr@(L _ (HsLet _ _)))
356 = sep [hang (ptext SLIT("let")) 2 (hsep [pprBinds binds, ptext SLIT("in")]),
359 ppr_expr (HsLet binds expr)
360 = sep [hang (ptext SLIT("let")) 2 (pprBinds binds),
361 hang (ptext SLIT("in")) 2 (ppr expr)]
363 ppr_expr (HsDo do_or_list_comp stmts body _) = pprDo do_or_list_comp stmts body
365 ppr_expr (ExplicitList _ exprs)
366 = brackets (fsep (punctuate comma (map ppr_lexpr exprs)))
368 ppr_expr (ExplicitPArr _ exprs)
369 = pa_brackets (fsep (punctuate comma (map ppr_lexpr exprs)))
371 ppr_expr (ExplicitTuple exprs boxity)
372 = tupleParens boxity (sep (punctuate comma (map ppr_lexpr exprs)))
374 ppr_expr (RecordCon con_id con_expr rbinds)
375 = pp_rbinds (ppr con_id) rbinds
377 ppr_expr (RecordUpd aexp rbinds _ _)
378 = pp_rbinds (pprParendExpr aexp) rbinds
380 ppr_expr (ExprWithTySig expr sig)
381 = hang (nest 2 (ppr_lexpr expr) <+> dcolon)
383 ppr_expr (ExprWithTySigOut expr sig)
384 = hang (nest 2 (ppr_lexpr expr) <+> dcolon)
387 ppr_expr (ArithSeq expr info) = brackets (ppr info)
388 ppr_expr (PArrSeq expr info) = pa_brackets (ppr info)
390 ppr_expr EWildPat = char '_'
391 ppr_expr (ELazyPat e) = char '~' <> pprParendExpr e
392 ppr_expr (EAsPat v e) = ppr v <> char '@' <> pprParendExpr e
394 ppr_expr (HsSCC lbl expr)
395 = sep [ ptext SLIT("_scc_") <+> doubleQuotes (ftext lbl), pprParendExpr expr ]
397 ppr_expr (TyLam tyvars expr)
398 = hang (hsep [ptext SLIT("/\\"),
399 hsep (map (pprBndr LambdaBind) tyvars),
403 ppr_expr (TyApp expr [ty])
404 = hang (ppr_lexpr expr) 4 (pprParendType ty)
406 ppr_expr (TyApp expr tys)
407 = hang (ppr_lexpr expr)
408 4 (brackets (interpp'SP tys))
410 ppr_expr (DictLam dictvars expr)
411 = hang (hsep [ptext SLIT("\\{-dict-}"),
412 hsep (map (pprBndr LambdaBind) dictvars),
416 ppr_expr (DictApp expr [dname])
417 = hang (ppr_lexpr expr) 4 (ppr dname)
419 ppr_expr (DictApp expr dnames)
420 = hang (ppr_lexpr expr)
421 4 (brackets (interpp'SP dnames))
423 ppr_expr (HsCoerce co_fn e) = ppr_expr e
425 ppr_expr (HsType id) = ppr id
427 ppr_expr (HsSpliceE s) = pprSplice s
428 ppr_expr (HsBracket b) = pprHsBracket b
429 ppr_expr (HsBracketOut e []) = ppr e
430 ppr_expr (HsBracketOut e ps) = ppr e $$ ptext SLIT("pending") <+> ppr ps
432 ppr_expr (HsProc pat (L _ (HsCmdTop cmd _ _ _)))
433 = hsep [ptext SLIT("proc"), ppr pat, ptext SLIT("->"), ppr cmd]
435 ppr_expr (HsArrApp arrow arg _ HsFirstOrderApp True)
436 = hsep [ppr_lexpr arrow, ptext SLIT("-<"), ppr_lexpr arg]
437 ppr_expr (HsArrApp arrow arg _ HsFirstOrderApp False)
438 = hsep [ppr_lexpr arg, ptext SLIT(">-"), ppr_lexpr arrow]
439 ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp True)
440 = hsep [ppr_lexpr arrow, ptext SLIT("-<<"), ppr_lexpr arg]
441 ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp False)
442 = hsep [ppr_lexpr arg, ptext SLIT(">>-"), ppr_lexpr arrow]
444 ppr_expr (HsArrForm (L _ (HsVar v)) (Just _) [arg1, arg2])
445 = sep [pprCmdArg (unLoc arg1), hsep [pprInfix v, pprCmdArg (unLoc arg2)]]
446 ppr_expr (HsArrForm op _ args)
447 = hang (ptext SLIT("(|") <> ppr_lexpr op)
448 4 (sep (map (pprCmdArg.unLoc) args) <> ptext SLIT("|)"))
450 pprCmdArg :: OutputableBndr id => HsCmdTop id -> SDoc
451 pprCmdArg (HsCmdTop cmd@(L _ (HsArrForm _ Nothing [])) _ _ _)
453 pprCmdArg (HsCmdTop cmd _ _ _)
454 = parens (ppr_lexpr cmd)
456 -- Put a var in backquotes if it's not an operator already
457 pprInfix :: Outputable name => name -> SDoc
458 pprInfix v | isOperator ppr_v = ppr_v
459 | otherwise = char '`' <> ppr_v <> char '`'
463 -- add parallel array brackets around a document
465 pa_brackets :: SDoc -> SDoc
466 pa_brackets p = ptext SLIT("[:") <> p <> ptext SLIT(":]")
469 Parenthesize unless very simple:
471 pprParendExpr :: OutputableBndr id => LHsExpr id -> SDoc
474 pp_as_was = ppr_lexpr expr
475 -- Using ppr_expr here avoids the call to 'deeper'
476 -- Not sure if that's always right.
483 HsIPVar _ -> pp_as_was
484 ExplicitList _ _ -> pp_as_was
485 ExplicitPArr _ _ -> pp_as_was
486 ExplicitTuple _ _ -> pp_as_was
488 HsBracket _ -> pp_as_was
489 HsBracketOut _ [] -> pp_as_was
491 _ -> parens pp_as_was
494 %************************************************************************
496 \subsection{Commands (in arrow abstractions)}
498 %************************************************************************
500 We re-use HsExpr to represent these.
503 type HsCmd id = HsExpr id
505 type LHsCmd id = LHsExpr id
507 data HsArrAppType = HsHigherOrderApp | HsFirstOrderApp
510 The legal constructors for commands are:
512 = HsArrApp ... -- as above
514 | HsArrForm ... -- as above
519 | HsLam (Match id) -- kappa
521 -- the renamer turns this one into HsArrForm
522 | OpApp (HsExpr id) -- left operand
523 (HsCmd id) -- operator
524 Fixity -- Renamer adds fixity; bottom until then
525 (HsCmd id) -- right operand
527 | HsPar (HsCmd id) -- parenthesised command
530 [Match id] -- bodies are HsCmd's
533 | HsIf (HsExpr id) -- predicate
534 (HsCmd id) -- then part
535 (HsCmd id) -- else part
538 | HsLet (HsLocalBinds id) -- let(rec)
541 | HsDo (HsStmtContext Name) -- The parameterisation is unimportant
542 -- because in this context we never use
543 -- the PatGuard or ParStmt variant
544 [Stmt id] -- HsExpr's are really HsCmd's
545 PostTcType -- Type of the whole expression
548 Top-level command, introducing a new arrow.
549 This may occur inside a proc (where the stack is empty) or as an
550 argument of a command-forming operator.
553 type LHsCmdTop id = Located (HsCmdTop id)
556 = HsCmdTop (LHsCmd id)
557 [PostTcType] -- types of inputs on the command's stack
558 PostTcType -- return type of the command
560 -- after type checking:
561 -- names used in the command's desugaring
564 %************************************************************************
566 \subsection{Record binds}
568 %************************************************************************
571 type HsRecordBinds id = [(Located id, LHsExpr id)]
573 recBindFields :: HsRecordBinds id -> [id]
574 recBindFields rbinds = [unLoc field | (field,_) <- rbinds]
576 pp_rbinds :: OutputableBndr id => SDoc -> HsRecordBinds id -> SDoc
577 pp_rbinds thing rbinds
579 4 (braces (sep (punctuate comma (map (pp_rbind) rbinds))))
581 pp_rbind (v, e) = hsep [pprBndr LetBind (unLoc v), char '=', ppr e]
586 %************************************************************************
588 \subsection{@Match@, @GRHSs@, and @GRHS@ datatypes}
590 %************************************************************************
592 @Match@es are sets of pattern bindings and right hand sides for
593 functions, patterns or case branches. For example, if a function @g@
599 then \tr{g} has two @Match@es: @(x,y) = y@ and @((x:ys),y) = y+1@.
601 It is always the case that each element of an @[Match]@ list has the
602 same number of @pats@s inside it. This corresponds to saying that
603 a function defined by pattern matching must have the same number of
604 patterns in each equation.
609 [LMatch id] -- The alternatives
610 PostTcType -- The type is the type of the entire group
611 -- t1 -> ... -> tn -> tr
612 -- where there are n patterns
614 type LMatch id = Located (Match id)
618 [LPat id] -- The patterns
619 (Maybe (LHsType id)) -- A type signature for the result of the match
620 -- Nothing after typechecking
623 matchGroupArity :: MatchGroup id -> Arity
624 matchGroupArity (MatchGroup [] _)
625 = panic "matchGroupArity" -- MatchGroup is never empty
626 matchGroupArity (MatchGroup (match:matches) _)
627 = ASSERT( all ((== n_pats) . length . hsLMatchPats) matches )
628 -- Assertion just checks that all the matches have the same number of pats
631 n_pats = length (hsLMatchPats match)
633 hsLMatchPats :: LMatch id -> [LPat id]
634 hsLMatchPats (L _ (Match pats _ _)) = pats
636 -- GRHSs are used both for pattern bindings and for Matches
638 = GRHSs [LGRHS id] -- Guarded RHSs
639 (HsLocalBinds id) -- The where clause
641 type LGRHS id = Located (GRHS id)
643 data GRHS id = GRHS [LStmt id] -- Guards
644 (LHsExpr id) -- Right hand side
647 We know the list must have at least one @Match@ in it.
650 pprMatches :: (OutputableBndr id) => HsMatchContext id -> MatchGroup id -> SDoc
651 pprMatches ctxt (MatchGroup matches _) = vcat (map (pprMatch ctxt) (map unLoc matches))
653 -- Exported to HsBinds, which can't see the defn of HsMatchContext
654 pprFunBind :: (OutputableBndr id) => id -> MatchGroup id -> SDoc
655 pprFunBind fun matches = pprMatches (FunRhs fun) matches
657 -- Exported to HsBinds, which can't see the defn of HsMatchContext
658 pprPatBind :: (OutputableBndr bndr, OutputableBndr id)
659 => LPat bndr -> GRHSs id -> SDoc
660 pprPatBind pat grhss = sep [ppr pat, nest 4 (pprGRHSs PatBindRhs grhss)]
663 pprMatch :: OutputableBndr id => HsMatchContext id -> Match id -> SDoc
664 pprMatch ctxt (Match pats maybe_ty grhss)
665 = pp_name ctxt <+> sep [sep (map ppr pats),
667 nest 2 (pprGRHSs ctxt grhss)]
669 pp_name (FunRhs fun) = ppr fun -- Not pprBndr; the AbsBinds will
670 -- have printed the signature
671 pp_name LambdaExpr = char '\\'
672 pp_name other = empty
674 ppr_maybe_ty = case maybe_ty of
675 Just ty -> dcolon <+> ppr ty
679 pprGRHSs :: OutputableBndr id => HsMatchContext id -> GRHSs id -> SDoc
680 pprGRHSs ctxt (GRHSs grhss binds)
681 = vcat (map (pprGRHS ctxt . unLoc) grhss)
683 (if isEmptyLocalBinds binds then empty
684 else text "where" $$ nest 4 (pprBinds binds))
686 pprGRHS :: OutputableBndr id => HsMatchContext id -> GRHS id -> SDoc
688 pprGRHS ctxt (GRHS [] expr)
691 pprGRHS ctxt (GRHS guards expr)
692 = sep [char '|' <+> interpp'SP guards, pp_rhs ctxt expr]
694 pp_rhs ctxt rhs = matchSeparator ctxt <+> pprDeeper (ppr rhs)
697 %************************************************************************
699 \subsection{Do stmts and list comprehensions}
701 %************************************************************************
704 type LStmt id = Located (Stmt id)
706 -- The SyntaxExprs in here are used *only* for do-notation, which
707 -- has rebindable syntax. Otherwise they are unused.
711 (SyntaxExpr id) -- The (>>=) operator
712 (SyntaxExpr id) -- The fail operator
713 -- The fail operator is noSyntaxExpr
714 -- if the pattern match can't fail
716 | ExprStmt (LHsExpr id)
717 (SyntaxExpr id) -- The (>>) operator
718 PostTcType -- Element type of the RHS (used for arrows)
720 | LetStmt (HsLocalBinds id)
722 -- ParStmts only occur in a list comprehension
723 | ParStmt [([LStmt id], [id])] -- After renaming, the ids are the binders
724 -- bound by the stmts and used subsequently
726 -- Recursive statement (see Note [RecStmt] below)
728 --- The next two fields are only valid after renaming
729 [id] -- The ids are a subset of the variables bound by the stmts
730 -- that are used in stmts that follow the RecStmt
732 [id] -- Ditto, but these variables are the "recursive" ones, that
733 -- are used before they are bound in the stmts of the RecStmt
734 -- From a type-checking point of view, these ones have to be monomorphic
736 --- These fields are only valid after typechecking
737 [PostTcExpr] -- These expressions correspond
738 -- 1-to-1 with the "recursive" [id], and are the expresions that
739 -- should be returned by the recursion. They may not quite be the
740 -- Ids themselves, because the Id may be *polymorphic*, but
741 -- the returned thing has to be *monomorphic*.
742 (DictBinds id) -- Method bindings of Ids bound by the RecStmt,
743 -- and used afterwards
746 ExprStmts are a bit tricky, because what they mean
747 depends on the context. Consider the following contexts:
749 A do expression of type (m res_ty)
750 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
751 * ExprStmt E any_ty: do { ....; E; ... }
753 Translation: E >> ...
755 A list comprehensions of type [elt_ty]
756 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
757 * ExprStmt E Bool: [ .. | .... E ]
759 [ .. | .... | ..., E | ... ]
761 Translation: if E then fail else ...
763 A guard list, guarding a RHS of type rhs_ty
764 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
765 * ExprStmt E Bool: f x | ..., E, ... = ...rhs...
767 Translation: if E then fail else ...
769 Array comprehensions are handled like list comprehensions -=chak
776 , RecStmt [a::forall a. a -> a, b]
778 [ BindStmt b (return x)
784 Here, the RecStmt binds a,b,c; but
785 - Only a,b are used in the stmts *following* the RecStmt,
786 This 'a' is *polymorphic'
787 - Only a,c are used in the stmts *inside* the RecStmt
788 *before* their bindings
789 This 'a' is monomorphic
791 Nota Bene: the two a's have different types, even though they
796 instance OutputableBndr id => Outputable (Stmt id) where
797 ppr stmt = pprStmt stmt
799 pprStmt (BindStmt pat expr _ _) = hsep [ppr pat, ptext SLIT("<-"), ppr expr]
800 pprStmt (LetStmt binds) = hsep [ptext SLIT("let"), pprBinds binds]
801 pprStmt (ExprStmt expr _ _) = ppr expr
802 pprStmt (ParStmt stmtss) = hsep (map (\stmts -> ptext SLIT("| ") <> ppr stmts) stmtss)
803 pprStmt (RecStmt segment _ _ _ _) = ptext SLIT("rec") <+> braces (vcat (map ppr segment))
805 pprDo :: OutputableBndr id => HsStmtContext any -> [LStmt id] -> LHsExpr id -> SDoc
806 pprDo DoExpr stmts body = ptext SLIT("do") <+> (vcat (map ppr stmts) $$ ppr body)
807 pprDo (MDoExpr _) stmts body = ptext SLIT("mdo") <+> (vcat (map ppr stmts) $$ ppr body)
808 pprDo ListComp stmts body = pprComp brackets stmts body
809 pprDo PArrComp stmts body = pprComp pa_brackets stmts body
810 pprDo other stmts body = panic "pprDo" -- PatGuard, ParStmtCxt
812 pprComp :: OutputableBndr id => (SDoc -> SDoc) -> [LStmt id] -> LHsExpr id -> SDoc
813 pprComp brack quals body
815 hang (ppr body <+> char '|')
819 %************************************************************************
821 Template Haskell quotation brackets
823 %************************************************************************
826 data HsSplice id = HsSplice -- $z or $(f 4)
827 id -- The id is just a unique name to
828 (LHsExpr id) -- identify this splice point
830 instance OutputableBndr id => Outputable (HsSplice id) where
833 pprSplice :: OutputableBndr id => HsSplice id -> SDoc
834 pprSplice (HsSplice n e) = char '$' <> brackets (ppr n) <> pprParendExpr e
837 data HsBracket id = ExpBr (LHsExpr id) -- [| expr |]
838 | PatBr (LPat id) -- [p| pat |]
839 | DecBr (HsGroup id) -- [d| decls |]
840 | TypBr (LHsType id) -- [t| type |]
841 | VarBr id -- 'x, ''T
843 instance OutputableBndr id => Outputable (HsBracket id) where
847 pprHsBracket (ExpBr e) = thBrackets empty (ppr e)
848 pprHsBracket (PatBr p) = thBrackets (char 'p') (ppr p)
849 pprHsBracket (DecBr d) = thBrackets (char 'd') (ppr d)
850 pprHsBracket (TypBr t) = thBrackets (char 't') (ppr t)
851 pprHsBracket (VarBr n) = char '\'' <> ppr n
852 -- Infelicity: can't show ' vs '', because
853 -- we can't ask n what its OccName is, because the
854 -- pretty-printer for HsExpr doesn't ask for NamedThings
855 -- But the pretty-printer for names will show the OccName class
857 thBrackets pp_kind pp_body = char '[' <> pp_kind <> char '|' <+>
858 pp_body <+> ptext SLIT("|]")
861 %************************************************************************
863 \subsection{Enumerations and list comprehensions}
865 %************************************************************************
870 | FromThen (LHsExpr id)
872 | FromTo (LHsExpr id)
874 | FromThenTo (LHsExpr id)
880 instance OutputableBndr id => Outputable (ArithSeqInfo id) where
881 ppr (From e1) = hcat [ppr e1, pp_dotdot]
882 ppr (FromThen e1 e2) = hcat [ppr e1, comma, space, ppr e2, pp_dotdot]
883 ppr (FromTo e1 e3) = hcat [ppr e1, pp_dotdot, ppr e3]
884 ppr (FromThenTo e1 e2 e3)
885 = hcat [ppr e1, comma, space, ppr e2, pp_dotdot, ppr e3]
887 pp_dotdot = ptext SLIT(" .. ")
891 %************************************************************************
893 \subsection{HsMatchCtxt}
895 %************************************************************************
898 data HsMatchContext id -- Context of a Match
899 = FunRhs id -- Function binding for f
900 | CaseAlt -- Guard on a case alternative
901 | LambdaExpr -- Pattern of a lambda
902 | ProcExpr -- Pattern of a proc
903 | PatBindRhs -- Pattern binding
904 | RecUpd -- Record update [used only in DsExpr to tell matchWrapper
905 -- what sort of runtime error message to generate]
906 | StmtCtxt (HsStmtContext id) -- Pattern of a do-stmt or list comprehension
909 data HsStmtContext id
912 | MDoExpr PostTcTable -- Recursive do-expression
913 -- (tiresomely, it needs table
914 -- of its return/bind ops)
915 | PArrComp -- Parallel array comprehension
916 | PatGuard (HsMatchContext id) -- Pattern guard for specified thing
917 | ParStmtCtxt (HsStmtContext id) -- A branch of a parallel stmt
921 isDoExpr :: HsStmtContext id -> Bool
922 isDoExpr DoExpr = True
923 isDoExpr (MDoExpr _) = True
924 isDoExpr other = False
928 matchSeparator (FunRhs _) = ptext SLIT("=")
929 matchSeparator CaseAlt = ptext SLIT("->")
930 matchSeparator LambdaExpr = ptext SLIT("->")
931 matchSeparator ProcExpr = ptext SLIT("->")
932 matchSeparator PatBindRhs = ptext SLIT("=")
933 matchSeparator (StmtCtxt _) = ptext SLIT("<-")
934 matchSeparator RecUpd = panic "unused"
938 pprMatchContext (FunRhs fun) = ptext SLIT("the definition of") <+> quotes (ppr fun)
939 pprMatchContext CaseAlt = ptext SLIT("a case alternative")
940 pprMatchContext RecUpd = ptext SLIT("a record-update construct")
941 pprMatchContext PatBindRhs = ptext SLIT("a pattern binding")
942 pprMatchContext LambdaExpr = ptext SLIT("a lambda abstraction")
943 pprMatchContext ProcExpr = ptext SLIT("an arrow abstraction")
944 pprMatchContext (StmtCtxt ctxt) = ptext SLIT("a pattern binding in") $$ pprStmtContext ctxt
946 pprStmtContext (ParStmtCtxt c) = sep [ptext SLIT("a parallel branch of"), pprStmtContext c]
947 pprStmtContext (PatGuard ctxt) = ptext SLIT("a pattern guard for") $$ pprMatchContext ctxt
948 pprStmtContext DoExpr = ptext SLIT("a 'do' expression")
949 pprStmtContext (MDoExpr _) = ptext SLIT("an 'mdo' expression")
950 pprStmtContext ListComp = ptext SLIT("a list comprehension")
951 pprStmtContext PArrComp = ptext SLIT("an array comprehension")
954 pprMatchRhsContext (FunRhs fun) = ptext SLIT("a right-hand side of function") <+> quotes (ppr fun)
955 pprMatchRhsContext CaseAlt = ptext SLIT("the body of a case alternative")
956 pprMatchRhsContext PatBindRhs = ptext SLIT("the right-hand side of a pattern binding")
957 pprMatchRhsContext LambdaExpr = ptext SLIT("the body of a lambda")
958 pprMatchRhsContext ProcExpr = ptext SLIT("the body of a proc")
959 pprMatchRhsContext other = panic "pprMatchRhsContext" -- RecUpd, StmtCtxt
961 -- Used for the result statement of comprehension
962 -- e.g. the 'e' in [ e | ... ]
963 -- or the 'r' in f x = r
964 pprStmtResultContext (PatGuard ctxt) = pprMatchRhsContext ctxt
965 pprStmtResultContext other = ptext SLIT("the result of") <+> pprStmtContext other
968 -- Used to generate the string for a *runtime* error message
969 matchContextErrString (FunRhs fun) = "function " ++ showSDoc (ppr fun)
970 matchContextErrString CaseAlt = "case"
971 matchContextErrString PatBindRhs = "pattern binding"
972 matchContextErrString RecUpd = "record update"
973 matchContextErrString LambdaExpr = "lambda"
974 matchContextErrString ProcExpr = "proc"
975 matchContextErrString (StmtCtxt (ParStmtCtxt c)) = matchContextErrString (StmtCtxt c)
976 matchContextErrString (StmtCtxt (PatGuard _)) = "pattern guard"
977 matchContextErrString (StmtCtxt DoExpr) = "'do' expression"
978 matchContextErrString (StmtCtxt (MDoExpr _)) = "'mdo' expression"
979 matchContextErrString (StmtCtxt ListComp) = "list comprehension"
980 matchContextErrString (StmtCtxt PArrComp) = "array comprehension"