2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
7 -- | Abstract Haskell syntax for expressions.
10 #include "HsVersions.h"
30 %************************************************************************
32 \subsection{Expressions proper}
34 %************************************************************************
37 -- * Expressions proper
39 type LHsExpr id = Located (HsExpr id)
41 -------------------------
42 -- | PostTcExpr is an evidence expression attached to the syntax tree by the
43 -- type checker (c.f. postTcType).
44 type PostTcExpr = HsExpr Id
45 -- | We use a PostTcTable where there are a bunch of pieces of evidence, more
46 -- than is convenient to keep individually.
47 type PostTcTable = [(Name, Id)]
49 noPostTcExpr :: PostTcExpr
50 noPostTcExpr = HsLit (HsString (fsLit "noPostTcExpr"))
52 noPostTcTable :: PostTcTable
55 -------------------------
56 -- | SyntaxExpr is like 'PostTcExpr', but it's filled in a little earlier,
57 -- by the renamer. It's used for rebindable syntax.
59 -- E.g. @(>>=)@ is filled in before the renamer by the appropriate 'Name' for
60 -- @(>>=)@, and then instantiated by the type checker with its type args
63 type SyntaxExpr id = HsExpr id
65 noSyntaxExpr :: SyntaxExpr id -- Before renaming, and sometimes after,
66 -- (if the syntax slot makes no sense)
67 noSyntaxExpr = HsLit (HsString (fsLit "noSyntaxExpr"))
70 type SyntaxTable id = [(Name, SyntaxExpr id)]
71 -- ^ Currently used only for 'CmdTop' (sigh)
73 -- * Before the renamer, this list is 'noSyntaxTable'
75 -- * After the renamer, it takes the form @[(std_name, HsVar actual_name)]@
76 -- For example, for the 'return' op of a monad
78 -- * normal case: @(GHC.Base.return, HsVar GHC.Base.return)@
80 -- * with rebindable syntax: @(GHC.Base.return, return_22)@
81 -- where @return_22@ is whatever @return@ is in scope
83 -- * After the type checker, it takes the form @[(std_name, <expression>)]@
84 -- where @<expression>@ is the evidence for the method
86 noSyntaxTable :: SyntaxTable id
90 -------------------------
91 -- | A Haskell expression.
93 = HsVar id -- ^ variable
94 | HsIPVar (IPName id) -- ^ implicit parameter
95 | HsOverLit (HsOverLit id) -- ^ Overloaded literals
97 | HsLit HsLit -- ^ Simple (non-overloaded) literals
99 | HsLam (MatchGroup id) -- Currently always a single match
101 | HsApp (LHsExpr id) (LHsExpr id) -- Application
103 -- Operator applications:
104 -- NB Bracketed ops such as (+) come out as Vars.
106 -- NB We need an expr for the operator in an OpApp/Section since
107 -- the typechecker may need to apply the operator to a few types.
109 | OpApp (LHsExpr id) -- left operand
110 (LHsExpr id) -- operator
111 Fixity -- Renamer adds fixity; bottom until then
112 (LHsExpr id) -- right operand
114 | NegApp (LHsExpr id) -- negated expr
115 (SyntaxExpr id) -- Name of 'negate'
117 | HsPar (LHsExpr id) -- parenthesised expr
119 | SectionL (LHsExpr id) -- operand
120 (LHsExpr id) -- operator
121 | SectionR (LHsExpr id) -- operator
122 (LHsExpr id) -- operand
124 | ExplicitTuple -- Used for explicit tuples and sections thereof
128 | HsCase (LHsExpr id)
131 | HsIf (LHsExpr id) -- predicate
132 (LHsExpr id) -- then part
133 (LHsExpr id) -- else part
135 | HsLet (HsLocalBinds id) -- let(rec)
138 | HsDo (HsStmtContext Name) -- The parameterisation is unimportant
139 -- because in this context we never use
140 -- the PatGuard or ParStmt variant
141 [LStmt id] -- "do":one or more stmts
142 (LHsExpr id) -- The body; the last expression in the
143 -- 'do' of [ body | ... ] in a list comp
144 PostTcType -- Type of the whole expression
146 | ExplicitList -- syntactic list
147 PostTcType -- Gives type of components of list
150 | ExplicitPArr -- syntactic parallel array: [:e1, ..., en:]
151 PostTcType -- type of elements of the parallel array
154 -- Record construction
155 | RecordCon (Located id) -- The constructor. After type checking
156 -- it's the dataConWrapId of the constructor
157 PostTcExpr -- Data con Id applied to type args
161 | RecordUpd (LHsExpr id)
163 -- (HsMatchGroup Id) -- Filled in by the type checker to be
164 -- -- a match that does the job
165 [DataCon] -- Filled in by the type checker to the
166 -- _non-empty_ list of DataCons that have
167 -- all the upd'd fields
168 [PostTcType] -- Argument types of *input* record type
169 [PostTcType] -- and *output* record type
170 -- For a type family, the arg types are of the *instance* tycon,
171 -- not the family tycon
173 | ExprWithTySig -- e :: type
177 | ExprWithTySigOut -- TRANSLATION
179 (LHsType Name) -- Retain the signature for
180 -- round-tripping purposes
182 | ArithSeq -- arithmetic sequence
186 | PArrSeq -- arith. sequence for parallel array
187 PostTcExpr -- [:e1..e2:] or [:e1, e2..e3:]
190 | HsSCC FastString -- "set cost centre" SCC pragma
191 (LHsExpr id) -- expr whose cost is to be measured
193 | HsCoreAnn FastString -- hdaume: core annotation
196 -----------------------------------------------------------
197 -- MetaHaskell Extensions
199 | HsBracket (HsBracket id)
201 | HsBracketOut (HsBracket Name) -- Output of the type checker is
203 [PendingSplice] -- renamed expression, plus
204 -- _typechecked_ splices to be
205 -- pasted back in by the desugarer
207 | HsSpliceE (HsSplice id)
209 | HsQuasiQuoteE (HsQuasiQuote id)
210 -- See Note [Quasi-quote overview] in TcSplice
212 -----------------------------------------------------------
213 -- Arrow notation extension
215 | HsProc (LPat id) -- arrow abstraction, proc
216 (LHsCmdTop id) -- body of the abstraction
217 -- always has an empty stack
219 ---------------------------------------
220 -- The following are commands, not expressions proper
222 | HsArrApp -- Arrow tail, or arrow application (f -< arg)
223 (LHsExpr id) -- arrow expression, f
224 (LHsExpr id) -- input expression, arg
225 PostTcType -- type of the arrow expressions f,
226 -- of the form a t t', where arg :: t
227 HsArrAppType -- higher-order (-<<) or first-order (-<)
228 Bool -- True => right-to-left (f -< arg)
229 -- False => left-to-right (arg >- f)
231 | HsArrForm -- Command formation, (| e cmd1 .. cmdn |)
232 (LHsExpr id) -- the operator
233 -- after type-checking, a type abstraction to be
234 -- applied to the type of the local environment tuple
235 (Maybe Fixity) -- fixity (filled in by the renamer), for forms that
236 -- were converted from OpApp's by the renamer
237 [LHsCmdTop id] -- argument commands
240 ---------------------------------------
241 -- Haskell program coverage (Hpc) Support
244 Int -- module-local tick number
245 [id] -- variables in scope
246 (LHsExpr id) -- sub-expression
249 Int -- module-local tick number for True
250 Int -- module-local tick number for False
251 (LHsExpr id) -- sub-expression
253 | HsTickPragma -- A pragma introduced tick
254 (FastString,(Int,Int),(Int,Int)) -- external span for this tick
257 ---------------------------------------
258 -- These constructors only appear temporarily in the parser.
259 -- The renamer translates them into the Right Thing.
261 | EWildPat -- wildcard
263 | EAsPat (Located id) -- as pattern
266 | EViewPat (LHsExpr id) -- view pattern
269 | ELazyPat (LHsExpr id) -- ~ pattern
271 | HsType (LHsType id) -- Explicit type argument; e.g f {| Int |} x y
273 ---------------------------------------
274 -- Finally, HsWrap appears only in typechecker output
276 | HsWrap HsWrapper -- TRANSLATION
279 -- HsTupArg is used for tuple sections
280 -- (,a,) is represented by ExplicitTuple [Mising ty1, Present a, Missing ty3]
281 -- Which in turn stands for (\x:ty1 \y:ty2. (x,a,y))
283 = Present (LHsExpr id) -- The argument
284 | Missing PostTcType -- The argument is missing, but this is its type
286 tupArgPresent :: HsTupArg id -> Bool
287 tupArgPresent (Present {}) = True
288 tupArgPresent (Missing {}) = False
290 type PendingSplice = (Name, LHsExpr Id) -- Typechecked splices, waiting to be
291 -- pasted back in by the desugarer
294 A @Dictionary@, unless of length 0 or 1, becomes a tuple. A
295 @ClassDictLam dictvars methods expr@ is, therefore:
297 \ x -> case x of ( dictvars-and-methods-tuple ) -> expr
301 instance OutputableBndr id => Outputable (HsExpr id) where
302 ppr expr = pprExpr expr
306 -----------------------
307 -- pprExpr, pprLExpr, pprBinds call pprDeeper;
308 -- the underscore versions do not
309 pprLExpr :: OutputableBndr id => LHsExpr id -> SDoc
310 pprLExpr (L _ e) = pprExpr e
312 pprExpr :: OutputableBndr id => HsExpr id -> SDoc
313 pprExpr e | isAtomicHsExpr e || isQuietHsExpr e = ppr_expr e
314 | otherwise = pprDeeper (ppr_expr e)
316 isQuietHsExpr :: HsExpr id -> Bool
317 -- Parentheses do display something, but it gives little info and
318 -- if we go deeper when we go inside them then we get ugly things
320 isQuietHsExpr (HsPar _) = True
321 -- applications don't display anything themselves
322 isQuietHsExpr (HsApp _ _) = True
323 isQuietHsExpr (OpApp _ _ _ _) = True
324 isQuietHsExpr _ = False
326 pprBinds :: (OutputableBndr idL, OutputableBndr idR)
327 => HsLocalBindsLR idL idR -> SDoc
328 pprBinds b = pprDeeper (ppr b)
330 -----------------------
331 ppr_lexpr :: OutputableBndr id => LHsExpr id -> SDoc
332 ppr_lexpr e = ppr_expr (unLoc e)
334 ppr_expr :: OutputableBndr id => HsExpr id -> SDoc
335 ppr_expr (HsVar v) = pprHsVar v
336 ppr_expr (HsIPVar v) = ppr v
337 ppr_expr (HsLit lit) = ppr lit
338 ppr_expr (HsOverLit lit) = ppr lit
339 ppr_expr (HsPar e) = parens (ppr_lexpr e)
341 ppr_expr (HsCoreAnn s e)
342 = vcat [ptext (sLit "HsCoreAnn") <+> ftext s, ppr_lexpr e]
344 ppr_expr (HsApp e1 e2)
345 = let (fun, args) = collect_args e1 [e2] in
346 hang (ppr_lexpr fun) 2 (sep (map pprParendExpr args))
348 collect_args (L _ (HsApp fun arg)) args = collect_args fun (arg:args)
349 collect_args fun args = (fun, args)
351 ppr_expr (OpApp e1 op _ e2)
353 HsVar v -> pp_infixly v
356 pp_e1 = pprDebugParendExpr e1 -- In debug mode, add parens
357 pp_e2 = pprDebugParendExpr e2 -- to make precedence clear
360 = hang (ppr op) 2 (sep [pp_e1, pp_e2])
363 = sep [nest 2 pp_e1, pprHsInfix v, nest 2 pp_e2]
365 ppr_expr (NegApp e _) = char '-' <+> pprDebugParendExpr e
367 ppr_expr (SectionL expr op)
369 HsVar v -> pp_infixly v
372 pp_expr = pprDebugParendExpr expr
374 pp_prefixly = hang (hsep [text " \\ x_ ->", ppr op])
375 4 (hsep [pp_expr, ptext (sLit "x_ )")])
376 pp_infixly v = (sep [pp_expr, pprHsInfix v])
378 ppr_expr (SectionR op expr)
380 HsVar v -> pp_infixly v
383 pp_expr = pprDebugParendExpr expr
385 pp_prefixly = hang (hsep [text "( \\ x_ ->", ppr op, ptext (sLit "x_")])
386 4 ((<>) pp_expr rparen)
388 = (sep [pprHsInfix v, pp_expr])
390 ppr_expr (ExplicitTuple exprs boxity)
391 = tupleParens boxity (fcat (ppr_tup_args exprs))
394 ppr_tup_args (Present e : es) = (ppr_lexpr e <> punc es) : ppr_tup_args es
395 ppr_tup_args (Missing _ : es) = punc es : ppr_tup_args es
397 punc (Present {} : _) = comma <> space
398 punc (Missing {} : _) = comma
401 --avoid using PatternSignatures for stage1 code portability
402 ppr_expr exprType@(HsLam matches)
403 = pprMatches (LambdaExpr `asTypeOf` idType exprType) matches
404 where idType :: HsExpr id -> HsMatchContext id; idType = undefined
406 ppr_expr exprType@(HsCase expr matches)
407 = sep [ sep [ptext (sLit "case"), nest 4 (ppr expr), ptext (sLit "of {")],
408 nest 2 (pprMatches (CaseAlt `asTypeOf` idType exprType) matches <+> char '}') ]
409 where idType :: HsExpr id -> HsMatchContext id; idType = undefined
411 ppr_expr (HsIf e1 e2 e3)
412 = sep [hsep [ptext (sLit "if"), nest 2 (ppr e1), ptext (sLit "then")],
417 -- special case: let ... in let ...
418 ppr_expr (HsLet binds expr@(L _ (HsLet _ _)))
419 = sep [hang (ptext (sLit "let")) 2 (hsep [pprBinds binds, ptext (sLit "in")]),
422 ppr_expr (HsLet binds expr)
423 = sep [hang (ptext (sLit "let")) 2 (pprBinds binds),
424 hang (ptext (sLit "in")) 2 (ppr expr)]
426 ppr_expr (HsDo do_or_list_comp stmts body _) = pprDo do_or_list_comp stmts body
428 ppr_expr (ExplicitList _ exprs)
429 = brackets (pprDeeperList fsep (punctuate comma (map ppr_lexpr exprs)))
431 ppr_expr (ExplicitPArr _ exprs)
432 = pa_brackets (pprDeeperList fsep (punctuate comma (map ppr_lexpr exprs)))
434 ppr_expr (RecordCon con_id _ rbinds)
435 = hang (ppr con_id) 2 (ppr rbinds)
437 ppr_expr (RecordUpd aexp rbinds _ _ _)
438 = hang (pprParendExpr aexp) 2 (ppr rbinds)
440 ppr_expr (ExprWithTySig expr sig)
441 = hang (nest 2 (ppr_lexpr expr) <+> dcolon)
443 ppr_expr (ExprWithTySigOut expr sig)
444 = hang (nest 2 (ppr_lexpr expr) <+> dcolon)
447 ppr_expr (ArithSeq _ info) = brackets (ppr info)
448 ppr_expr (PArrSeq _ info) = pa_brackets (ppr info)
450 ppr_expr EWildPat = char '_'
451 ppr_expr (ELazyPat e) = char '~' <> pprParendExpr e
452 ppr_expr (EAsPat v e) = ppr v <> char '@' <> pprParendExpr e
453 ppr_expr (EViewPat p e) = ppr p <+> ptext (sLit "->") <+> ppr e
455 ppr_expr (HsSCC lbl expr)
456 = sep [ ptext (sLit "_scc_") <+> doubleQuotes (ftext lbl),
459 ppr_expr (HsWrap co_fn e) = pprHsWrapper (pprExpr e) co_fn
460 ppr_expr (HsType id) = ppr id
462 ppr_expr (HsSpliceE s) = pprSplice s
463 ppr_expr (HsBracket b) = pprHsBracket b
464 ppr_expr (HsBracketOut e []) = ppr e
465 ppr_expr (HsBracketOut e ps) = ppr e $$ ptext (sLit "pending") <+> ppr ps
466 ppr_expr (HsQuasiQuoteE qq) = ppr qq
468 ppr_expr (HsProc pat (L _ (HsCmdTop cmd _ _ _)))
469 = hsep [ptext (sLit "proc"), ppr pat, ptext (sLit "->"), ppr cmd]
471 ppr_expr (HsTick tickId vars exp)
472 = hcat [ptext (sLit "tick<"),
475 hsep (map pprHsVar vars),
478 ppr_expr (HsBinTick tickIdTrue tickIdFalse exp)
479 = hcat [ptext (sLit "bintick<"),
484 ppr exp,ptext (sLit ")")]
485 ppr_expr (HsTickPragma externalSrcLoc exp)
486 = hcat [ptext (sLit "tickpragma<"),
492 ppr_expr (HsArrApp arrow arg _ HsFirstOrderApp True)
493 = hsep [ppr_lexpr arrow, ptext (sLit "-<"), ppr_lexpr arg]
494 ppr_expr (HsArrApp arrow arg _ HsFirstOrderApp False)
495 = hsep [ppr_lexpr arg, ptext (sLit ">-"), ppr_lexpr arrow]
496 ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp True)
497 = hsep [ppr_lexpr arrow, ptext (sLit "-<<"), ppr_lexpr arg]
498 ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp False)
499 = hsep [ppr_lexpr arg, ptext (sLit ">>-"), ppr_lexpr arrow]
501 ppr_expr (HsArrForm (L _ (HsVar v)) (Just _) [arg1, arg2])
502 = sep [pprCmdArg (unLoc arg1), hsep [pprHsInfix v, pprCmdArg (unLoc arg2)]]
503 ppr_expr (HsArrForm op _ args)
504 = hang (ptext (sLit "(|") <> ppr_lexpr op)
505 4 (sep (map (pprCmdArg.unLoc) args) <> ptext (sLit "|)"))
507 pprCmdArg :: OutputableBndr id => HsCmdTop id -> SDoc
508 pprCmdArg (HsCmdTop cmd@(L _ (HsArrForm _ Nothing [])) _ _ _)
510 pprCmdArg (HsCmdTop cmd _ _ _)
511 = parens (ppr_lexpr cmd)
513 instance OutputableBndr id => Outputable (HsCmdTop id) where
516 -- add parallel array brackets around a document
518 pa_brackets :: SDoc -> SDoc
519 pa_brackets p = ptext (sLit "[:") <> p <> ptext (sLit ":]")
522 HsSyn records exactly where the user put parens, with HsPar.
523 So generally speaking we print without adding any parens.
524 However, some code is internally generated, and in some places
525 parens are absolutely required; so for these places we use
526 pprParendExpr (but don't print double parens of course).
528 For operator applications we don't add parens, because the oprerator
529 fixities should do the job, except in debug mode (-dppr-debug) so we
530 can see the structure of the parse tree.
533 pprDebugParendExpr :: OutputableBndr id => LHsExpr id -> SDoc
534 pprDebugParendExpr expr
535 = getPprStyle (\sty ->
536 if debugStyle sty then pprParendExpr expr
539 pprParendExpr :: OutputableBndr id => LHsExpr id -> SDoc
542 pp_as_was = pprLExpr expr
543 -- Using pprLExpr makes sure that we go 'deeper'
544 -- I think that is usually (always?) right
547 ArithSeq {} -> pp_as_was
548 PArrSeq {} -> pp_as_was
549 HsLit {} -> pp_as_was
550 HsOverLit {} -> pp_as_was
551 HsVar {} -> pp_as_was
552 HsIPVar {} -> pp_as_was
553 ExplicitTuple {} -> pp_as_was
554 ExplicitList {} -> pp_as_was
555 ExplicitPArr {} -> pp_as_was
556 HsPar {} -> pp_as_was
557 HsBracket {} -> pp_as_was
558 HsBracketOut _ [] -> pp_as_was
560 | isListCompExpr sc -> pp_as_was
561 _ -> parens pp_as_was
563 isAtomicHsExpr :: HsExpr id -> Bool -- A single token
564 isAtomicHsExpr (HsVar {}) = True
565 isAtomicHsExpr (HsLit {}) = True
566 isAtomicHsExpr (HsOverLit {}) = True
567 isAtomicHsExpr (HsIPVar {}) = True
568 isAtomicHsExpr (HsWrap _ e) = isAtomicHsExpr e
569 isAtomicHsExpr (HsPar e) = isAtomicHsExpr (unLoc e)
570 isAtomicHsExpr _ = False
573 %************************************************************************
575 \subsection{Commands (in arrow abstractions)}
577 %************************************************************************
579 We re-use HsExpr to represent these.
582 type HsCmd id = HsExpr id
584 type LHsCmd id = LHsExpr id
586 data HsArrAppType = HsHigherOrderApp | HsFirstOrderApp
589 The legal constructors for commands are:
591 = HsArrApp ... -- as above
593 | HsArrForm ... -- as above
598 | HsLam (Match id) -- kappa
600 -- the renamer turns this one into HsArrForm
601 | OpApp (HsExpr id) -- left operand
602 (HsCmd id) -- operator
603 Fixity -- Renamer adds fixity; bottom until then
604 (HsCmd id) -- right operand
606 | HsPar (HsCmd id) -- parenthesised command
609 [Match id] -- bodies are HsCmd's
612 | HsIf (HsExpr id) -- predicate
613 (HsCmd id) -- then part
614 (HsCmd id) -- else part
617 | HsLet (HsLocalBinds id) -- let(rec)
620 | HsDo (HsStmtContext Name) -- The parameterisation is unimportant
621 -- because in this context we never use
622 -- the PatGuard or ParStmt variant
623 [Stmt id] -- HsExpr's are really HsCmd's
624 PostTcType -- Type of the whole expression
627 Top-level command, introducing a new arrow.
628 This may occur inside a proc (where the stack is empty) or as an
629 argument of a command-forming operator.
632 type LHsCmdTop id = Located (HsCmdTop id)
635 = HsCmdTop (LHsCmd id)
636 [PostTcType] -- types of inputs on the command's stack
637 PostTcType -- return type of the command
638 (SyntaxTable id) -- after type checking:
639 -- names used in the command's desugaring
642 %************************************************************************
644 \subsection{Record binds}
646 %************************************************************************
649 type HsRecordBinds id = HsRecFields id (LHsExpr id)
654 %************************************************************************
656 \subsection{@Match@, @GRHSs@, and @GRHS@ datatypes}
658 %************************************************************************
660 @Match@es are sets of pattern bindings and right hand sides for
661 functions, patterns or case branches. For example, if a function @g@
667 then \tr{g} has two @Match@es: @(x,y) = y@ and @((x:ys),y) = y+1@.
669 It is always the case that each element of an @[Match]@ list has the
670 same number of @pats@s inside it. This corresponds to saying that
671 a function defined by pattern matching must have the same number of
672 patterns in each equation.
677 [LMatch id] -- The alternatives
678 PostTcType -- The type is the type of the entire group
679 -- t1 -> ... -> tn -> tr
680 -- where there are n patterns
682 type LMatch id = Located (Match id)
686 [LPat id] -- The patterns
687 (Maybe (LHsType id)) -- A type signature for the result of the match
688 -- Nothing after typechecking
691 isEmptyMatchGroup :: MatchGroup id -> Bool
692 isEmptyMatchGroup (MatchGroup ms _) = null ms
694 matchGroupArity :: MatchGroup id -> Arity
695 matchGroupArity (MatchGroup [] _)
696 = panic "matchGroupArity" -- Precondition: MatchGroup is non-empty
697 matchGroupArity (MatchGroup (match:matches) _)
698 = ASSERT( all ((== n_pats) . length . hsLMatchPats) matches )
699 -- Assertion just checks that all the matches have the same number of pats
702 n_pats = length (hsLMatchPats match)
704 hsLMatchPats :: LMatch id -> [LPat id]
705 hsLMatchPats (L _ (Match pats _ _)) = pats
707 -- | GRHSs are used both for pattern bindings and for Matches
710 grhssGRHSs :: [LGRHS id], -- ^ Guarded RHSs
711 grhssLocalBinds :: (HsLocalBinds id) -- ^ The where clause
714 type LGRHS id = Located (GRHS id)
716 -- | Guarded Right Hand Side.
717 data GRHS id = GRHS [LStmt id] -- Guards
718 (LHsExpr id) -- Right hand side
721 We know the list must have at least one @Match@ in it.
724 pprMatches :: (OutputableBndr idL, OutputableBndr idR) => HsMatchContext idL -> MatchGroup idR -> SDoc
725 pprMatches ctxt (MatchGroup matches _)
726 = vcat (map (pprMatch ctxt) (map unLoc matches))
727 -- Don't print the type; it's only a place-holder before typechecking
729 -- Exported to HsBinds, which can't see the defn of HsMatchContext
730 pprFunBind :: (OutputableBndr idL, OutputableBndr idR) => idL -> Bool -> MatchGroup idR -> SDoc
731 pprFunBind fun inf matches = pprMatches (FunRhs fun inf) matches
733 -- Exported to HsBinds, which can't see the defn of HsMatchContext
734 pprPatBind :: (OutputableBndr bndr, OutputableBndr id)
735 => LPat bndr -> GRHSs id -> SDoc
736 pprPatBind pat ty@(grhss)
737 = sep [ppr pat, nest 4 (pprGRHSs (PatBindRhs `asTypeOf` idType ty) grhss)]
738 --avoid using PatternSignatures for stage1 code portability
739 where idType :: GRHSs id -> HsMatchContext id; idType = undefined
742 pprMatch :: (OutputableBndr idL, OutputableBndr idR) => HsMatchContext idL -> Match idR -> SDoc
743 pprMatch ctxt (Match pats maybe_ty grhss)
744 = herald <+> sep [sep (map ppr other_pats),
746 nest 2 (pprGRHSs ctxt grhss)]
751 | not is_infix -> (ppr fun, pats)
753 -- Not pprBndr; the AbsBinds will
754 -- have printed the signature
756 | null pats3 -> (pp_infix, [])
759 | otherwise -> (parens pp_infix, pats3)
762 (pat1:pat2:pats3) = pats
763 pp_infix = ppr pat1 <+> ppr fun <+> ppr pat2
765 LambdaExpr -> (char '\\', pats)
768 ppr_maybe_ty = case maybe_ty of
769 Just ty -> dcolon <+> ppr ty
773 pprGRHSs :: (OutputableBndr idL, OutputableBndr idR)
774 => HsMatchContext idL -> GRHSs idR -> SDoc
775 pprGRHSs ctxt (GRHSs grhss binds)
776 = vcat (map (pprGRHS ctxt . unLoc) grhss)
777 $$ if isEmptyLocalBinds binds then empty
778 else text "where" $$ nest 4 (pprBinds binds)
780 pprGRHS :: (OutputableBndr idL, OutputableBndr idR)
781 => HsMatchContext idL -> GRHS idR -> SDoc
783 pprGRHS ctxt (GRHS [] expr)
786 pprGRHS ctxt (GRHS guards expr)
787 = sep [char '|' <+> interpp'SP guards, pp_rhs ctxt expr]
789 pp_rhs :: OutputableBndr idR => HsMatchContext idL -> LHsExpr idR -> SDoc
790 pp_rhs ctxt rhs = matchSeparator ctxt <+> pprDeeper (ppr rhs)
793 %************************************************************************
795 \subsection{Do stmts and list comprehensions}
797 %************************************************************************
800 type LStmt id = Located (StmtLR id id)
801 type LStmtLR idL idR = Located (StmtLR idL idR)
803 type Stmt id = StmtLR id id
805 data GroupByClause id
806 = GroupByNothing (LHsExpr id) -- Using expression, i.e.
807 -- "then group using f" ==> GroupByNothing f
808 | GroupBySomething (Either (LHsExpr id) (SyntaxExpr id)) (LHsExpr id)
809 -- "then group using f by e" ==> GroupBySomething (Left f) e
810 -- "then group by e" ==> GroupBySomething (Right _) e: in
811 -- this case the expression is filled
814 -- The SyntaxExprs in here are used *only* for do-notation, which
815 -- has rebindable syntax. Otherwise they are unused.
817 = BindStmt (LPat idL)
819 (SyntaxExpr idR) -- The (>>=) operator
820 (SyntaxExpr idR) -- The fail operator
821 -- The fail operator is noSyntaxExpr
822 -- if the pattern match can't fail
824 | ExprStmt (LHsExpr idR)
825 (SyntaxExpr idR) -- The (>>) operator
826 PostTcType -- Element type of the RHS (used for arrows)
828 | LetStmt (HsLocalBindsLR idL idR)
830 -- ParStmts only occur in a list comprehension
831 | ParStmt [([LStmt idL], [idR])]
832 -- After renaming, the ids are the binders bound by the stmts and used
835 | TransformStmt ([LStmt idL], [idR]) (LHsExpr idR) (Maybe (LHsExpr idR))
836 -- After renaming, the IDs are the binders occurring within this
837 -- transform statement that are used after it
838 -- "qs, then f by e" ==> TransformStmt (qs, binders) f (Just e)
839 -- "qs, then f" ==> TransformStmt (qs, binders) f Nothing
841 | GroupStmt ([LStmt idL], [(idR, idR)]) (GroupByClause idR)
842 -- After renaming, the IDs are the binders occurring within this
843 -- transform statement that are used after it which are paired with
844 -- the names which they group over in statements
846 -- Recursive statement (see Note [RecStmt] below)
847 | RecStmt [LStmtLR idL idR]
848 --- The next two fields are only valid after renaming
849 [idR] -- The ids are a subset of the variables bound by the
850 -- stmts that are used in stmts that follow the RecStmt
852 [idR] -- Ditto, but these variables are the "recursive" ones,
853 -- that are used before they are bound in the stmts of
854 -- the RecStmt. From a type-checking point of view,
855 -- these ones have to be monomorphic
857 --- These fields are only valid after typechecking
858 [PostTcExpr] -- These expressions correspond 1-to-1 with
859 -- the "recursive" [id], and are the
860 -- expressions that should be returned by
862 -- They may not quite be the Ids themselves,
863 -- because the Id may be *polymorphic*, but
864 -- the returned thing has to be *monomorphic*.
865 (DictBinds idR) -- Method bindings of Ids bound by the
866 -- RecStmt, and used afterwards
869 ExprStmts are a bit tricky, because what they mean
870 depends on the context. Consider the following contexts:
872 A do expression of type (m res_ty)
873 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
874 * ExprStmt E any_ty: do { ....; E; ... }
876 Translation: E >> ...
878 A list comprehensions of type [elt_ty]
879 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
880 * ExprStmt E Bool: [ .. | .... E ]
882 [ .. | .... | ..., E | ... ]
884 Translation: if E then fail else ...
886 A guard list, guarding a RHS of type rhs_ty
887 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
888 * ExprStmt E Bool: f x | ..., E, ... = ...rhs...
890 Translation: if E then fail else ...
892 Array comprehensions are handled like list comprehensions -=chak
899 , RecStmt [a::forall a. a -> a, b]
901 [ BindStmt b (return x)
907 Here, the RecStmt binds a,b,c; but
908 - Only a,b are used in the stmts *following* the RecStmt,
909 This 'a' is *polymorphic'
910 - Only a,c are used in the stmts *inside* the RecStmt
911 *before* their bindings
912 This 'a' is monomorphic
914 Nota Bene: the two a's have different types, even though they
919 instance (OutputableBndr idL, OutputableBndr idR) => Outputable (StmtLR idL idR) where
920 ppr stmt = pprStmt stmt
922 pprStmt :: (OutputableBndr idL, OutputableBndr idR) => (StmtLR idL idR) -> SDoc
923 pprStmt (BindStmt pat expr _ _) = hsep [ppr pat, ptext (sLit "<-"), ppr expr]
924 pprStmt (LetStmt binds) = hsep [ptext (sLit "let"), pprBinds binds]
925 pprStmt (ExprStmt expr _ _) = ppr expr
926 pprStmt (ParStmt stmtss) = hsep (map doStmts stmtss)
927 where doStmts stmts = ptext (sLit "| ") <> ppr stmts
928 pprStmt (TransformStmt (stmts, _) usingExpr maybeByExpr)
929 = (hsep [stmtsDoc, ptext (sLit "then"), ppr usingExpr, byExprDoc])
930 where stmtsDoc = interpp'SP stmts
931 byExprDoc = maybe empty (\byExpr -> hsep [ptext (sLit "by"), ppr byExpr]) maybeByExpr
932 pprStmt (GroupStmt (stmts, _) groupByClause) = (hsep [stmtsDoc, ptext (sLit "then group"), pprGroupByClause groupByClause])
933 where stmtsDoc = interpp'SP stmts
934 pprStmt (RecStmt segment _ _ _ _) = ptext (sLit "rec") <+> braces (vcat (map ppr segment))
936 pprGroupByClause :: (OutputableBndr id) => GroupByClause id -> SDoc
937 pprGroupByClause (GroupByNothing usingExpr) = hsep [ptext (sLit "using"), ppr usingExpr]
938 pprGroupByClause (GroupBySomething eitherUsingExpr byExpr) = hsep [ptext (sLit "by"), ppr byExpr, usingExprDoc]
939 where usingExprDoc = either (\usingExpr -> hsep [ptext (sLit "using"), ppr usingExpr]) (const empty) eitherUsingExpr
941 pprDo :: OutputableBndr id => HsStmtContext any -> [LStmt id] -> LHsExpr id -> SDoc
942 pprDo DoExpr stmts body = ptext (sLit "do") <+> ppr_do_stmts stmts body
943 pprDo (MDoExpr _) stmts body = ptext (sLit "mdo") <+> ppr_do_stmts stmts body
944 pprDo ListComp stmts body = pprComp brackets stmts body
945 pprDo PArrComp stmts body = pprComp pa_brackets stmts body
946 pprDo _ _ _ = panic "pprDo" -- PatGuard, ParStmtCxt
948 ppr_do_stmts :: OutputableBndr id => [LStmt id] -> LHsExpr id -> SDoc
949 -- Print a bunch of do stmts, with explicit braces and semicolons,
950 -- so that we are not vulnerable to layout bugs
951 ppr_do_stmts stmts body
952 = lbrace <+> pprDeeperList vcat ([ ppr s <> semi | s <- stmts] ++ [ppr body])
955 pprComp :: OutputableBndr id => (SDoc -> SDoc) -> [LStmt id] -> LHsExpr id -> SDoc
956 pprComp brack quals body
958 hang (ppr body <+> char '|')
962 %************************************************************************
964 Template Haskell quotation brackets
966 %************************************************************************
969 data HsSplice id = HsSplice -- $z or $(f 4)
970 id -- The id is just a unique name to
971 (LHsExpr id) -- identify this splice point
973 instance OutputableBndr id => Outputable (HsSplice id) where
976 pprSplice :: OutputableBndr id => HsSplice id -> SDoc
977 pprSplice (HsSplice n e)
978 = char '$' <> ifPprDebug (brackets (ppr n)) <> pprParendExpr e
981 data HsBracket id = ExpBr (LHsExpr id) -- [| expr |]
982 | PatBr (LPat id) -- [p| pat |]
983 | DecBr (HsGroup id) -- [d| decls |]
984 | TypBr (LHsType id) -- [t| type |]
985 | VarBr id -- 'x, ''T
987 instance OutputableBndr id => Outputable (HsBracket id) where
991 pprHsBracket :: OutputableBndr id => HsBracket id -> SDoc
992 pprHsBracket (ExpBr e) = thBrackets empty (ppr e)
993 pprHsBracket (PatBr p) = thBrackets (char 'p') (ppr p)
994 pprHsBracket (DecBr d) = thBrackets (char 'd') (ppr d)
995 pprHsBracket (TypBr t) = thBrackets (char 't') (ppr t)
996 pprHsBracket (VarBr n) = char '\'' <> ppr n
997 -- Infelicity: can't show ' vs '', because
998 -- we can't ask n what its OccName is, because the
999 -- pretty-printer for HsExpr doesn't ask for NamedThings
1000 -- But the pretty-printer for names will show the OccName class
1002 thBrackets :: SDoc -> SDoc -> SDoc
1003 thBrackets pp_kind pp_body = char '[' <> pp_kind <> char '|' <+>
1004 pp_body <+> ptext (sLit "|]")
1007 %************************************************************************
1009 \subsection{Enumerations and list comprehensions}
1011 %************************************************************************
1014 data ArithSeqInfo id
1016 | FromThen (LHsExpr id)
1018 | FromTo (LHsExpr id)
1020 | FromThenTo (LHsExpr id)
1026 instance OutputableBndr id => Outputable (ArithSeqInfo id) where
1027 ppr (From e1) = hcat [ppr e1, pp_dotdot]
1028 ppr (FromThen e1 e2) = hcat [ppr e1, comma, space, ppr e2, pp_dotdot]
1029 ppr (FromTo e1 e3) = hcat [ppr e1, pp_dotdot, ppr e3]
1030 ppr (FromThenTo e1 e2 e3)
1031 = hcat [ppr e1, comma, space, ppr e2, pp_dotdot, ppr e3]
1034 pp_dotdot = ptext (sLit " .. ")
1038 %************************************************************************
1040 \subsection{HsMatchCtxt}
1042 %************************************************************************
1045 data HsMatchContext id -- Context of a Match
1046 = FunRhs id Bool -- Function binding for f; True <=> written infix
1047 | CaseAlt -- Patterns and guards on a case alternative
1048 | LambdaExpr -- Patterns of a lambda
1049 | ProcExpr -- Patterns of a proc
1050 | PatBindRhs -- Patterns in the *guards* of a pattern binding
1051 | RecUpd -- Record update [used only in DsExpr to
1052 -- tell matchWrapper what sort of
1053 -- runtime error message to generate]
1054 | StmtCtxt (HsStmtContext id) -- Pattern of a do-stmt or list comprehension
1057 data HsStmtContext id
1060 | MDoExpr PostTcTable -- Recursive do-expression
1061 -- (tiresomely, it needs table
1062 -- of its return/bind ops)
1063 | PArrComp -- Parallel array comprehension
1064 | PatGuard (HsMatchContext id) -- Pattern guard for specified thing
1065 | ParStmtCtxt (HsStmtContext id) -- A branch of a parallel stmt
1066 | TransformStmtCtxt (HsStmtContext id) -- A branch of a transform stmt
1070 isDoExpr :: HsStmtContext id -> Bool
1071 isDoExpr DoExpr = True
1072 isDoExpr (MDoExpr _) = True
1075 isListCompExpr :: HsStmtContext id -> Bool
1076 isListCompExpr ListComp = True
1077 isListCompExpr PArrComp = True
1078 isListCompExpr _ = False
1082 matchSeparator :: HsMatchContext id -> SDoc
1083 matchSeparator (FunRhs {}) = ptext (sLit "=")
1084 matchSeparator CaseAlt = ptext (sLit "->")
1085 matchSeparator LambdaExpr = ptext (sLit "->")
1086 matchSeparator ProcExpr = ptext (sLit "->")
1087 matchSeparator PatBindRhs = ptext (sLit "=")
1088 matchSeparator (StmtCtxt _) = ptext (sLit "<-")
1089 matchSeparator RecUpd = panic "unused"
1093 pprMatchContext :: Outputable id => HsMatchContext id -> SDoc
1094 pprMatchContext (FunRhs fun _) = ptext (sLit "the definition of")
1095 <+> quotes (ppr fun)
1096 pprMatchContext CaseAlt = ptext (sLit "a case alternative")
1097 pprMatchContext RecUpd = ptext (sLit "a record-update construct")
1098 pprMatchContext PatBindRhs = ptext (sLit "a pattern binding")
1099 pprMatchContext LambdaExpr = ptext (sLit "a lambda abstraction")
1100 pprMatchContext ProcExpr = ptext (sLit "an arrow abstraction")
1101 pprMatchContext (StmtCtxt ctxt) = ptext (sLit "a pattern binding in")
1102 $$ pprStmtContext ctxt
1104 pprStmtContext :: Outputable id => HsStmtContext id -> SDoc
1105 pprStmtContext (ParStmtCtxt c)
1106 = sep [ptext (sLit "a parallel branch of"), pprStmtContext c]
1107 pprStmtContext (TransformStmtCtxt c)
1108 = sep [ptext (sLit "a transformed branch of"), pprStmtContext c]
1109 pprStmtContext (PatGuard ctxt)
1110 = ptext (sLit "a pattern guard for") $$ pprMatchContext ctxt
1111 pprStmtContext DoExpr = ptext (sLit "a 'do' expression")
1112 pprStmtContext (MDoExpr _) = ptext (sLit "an 'mdo' expression")
1113 pprStmtContext ListComp = ptext (sLit "a list comprehension")
1114 pprStmtContext PArrComp = ptext (sLit "an array comprehension")
1117 pprMatchRhsContext (FunRhs fun) = ptext (sLit "a right-hand side of function") <+> quotes (ppr fun)
1118 pprMatchRhsContext CaseAlt = ptext (sLit "the body of a case alternative")
1119 pprMatchRhsContext PatBindRhs = ptext (sLit "the right-hand side of a pattern binding")
1120 pprMatchRhsContext LambdaExpr = ptext (sLit "the body of a lambda")
1121 pprMatchRhsContext ProcExpr = ptext (sLit "the body of a proc")
1122 pprMatchRhsContext other = panic "pprMatchRhsContext" -- RecUpd, StmtCtxt
1124 -- Used for the result statement of comprehension
1125 -- e.g. the 'e' in [ e | ... ]
1126 -- or the 'r' in f x = r
1127 pprStmtResultContext (PatGuard ctxt) = pprMatchRhsContext ctxt
1128 pprStmtResultContext other = ptext (sLit "the result of") <+> pprStmtContext other
1131 -- Used to generate the string for a *runtime* error message
1132 matchContextErrString :: Outputable id => HsMatchContext id -> SDoc
1133 matchContextErrString (FunRhs fun _) = ptext (sLit "function") <+> ppr fun
1134 matchContextErrString CaseAlt = ptext (sLit "case")
1135 matchContextErrString PatBindRhs = ptext (sLit "pattern binding")
1136 matchContextErrString RecUpd = ptext (sLit "record update")
1137 matchContextErrString LambdaExpr = ptext (sLit "lambda")
1138 matchContextErrString ProcExpr = ptext (sLit "proc")
1139 matchContextErrString (StmtCtxt (ParStmtCtxt c)) = matchContextErrString (StmtCtxt c)
1140 matchContextErrString (StmtCtxt (TransformStmtCtxt c)) = matchContextErrString (StmtCtxt c)
1141 matchContextErrString (StmtCtxt (PatGuard _)) = ptext (sLit "pattern guard")
1142 matchContextErrString (StmtCtxt DoExpr) = ptext (sLit "'do' expression")
1143 matchContextErrString (StmtCtxt (MDoExpr _)) = ptext (sLit "'mdo' expression")
1144 matchContextErrString (StmtCtxt ListComp) = ptext (sLit "list comprehension")
1145 matchContextErrString (StmtCtxt PArrComp) = ptext (sLit "array comprehension")
1149 pprMatchInCtxt :: (OutputableBndr idL, OutputableBndr idR)
1150 => HsMatchContext idL -> Match idR -> SDoc
1151 pprMatchInCtxt ctxt match = hang (ptext (sLit "In") <+> pprMatchContext ctxt <> colon)
1152 4 (pprMatch ctxt match)
1154 pprStmtInCtxt :: (OutputableBndr idL, OutputableBndr idR)
1155 => HsStmtContext idL -> StmtLR idL idR -> SDoc
1156 pprStmtInCtxt ctxt stmt = hang (ptext (sLit "In a stmt of") <+> pprStmtContext ctxt <> colon)