2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 {-# LANGUAGE DeriveDataTypeable #-}
8 -- | Abstract Haskell syntax for expressions.
11 #include "HsVersions.h"
26 import Util( dropTail )
27 import StaticFlags( opt_PprStyle_Debug )
32 import Data.Data hiding (Fixity)
36 %************************************************************************
38 \subsection{Expressions proper}
40 %************************************************************************
43 -- * Expressions proper
45 type LHsExpr id = Located (HsExpr id)
47 -------------------------
48 -- | PostTcExpr is an evidence expression attached to the syntax tree by the
49 -- type checker (c.f. postTcType).
50 type PostTcExpr = HsExpr Id
51 -- | We use a PostTcTable where there are a bunch of pieces of evidence, more
52 -- than is convenient to keep individually.
53 type PostTcTable = [(Name, PostTcExpr)]
55 noPostTcExpr :: PostTcExpr
56 noPostTcExpr = HsLit (HsString (fsLit "noPostTcExpr"))
58 noPostTcTable :: PostTcTable
61 -------------------------
62 -- | SyntaxExpr is like 'PostTcExpr', but it's filled in a little earlier,
63 -- by the renamer. It's used for rebindable syntax.
65 -- E.g. @(>>=)@ is filled in before the renamer by the appropriate 'Name' for
66 -- @(>>=)@, and then instantiated by the type checker with its type args
69 type SyntaxExpr id = HsExpr id
71 noSyntaxExpr :: SyntaxExpr id -- Before renaming, and sometimes after,
72 -- (if the syntax slot makes no sense)
73 noSyntaxExpr = HsLit (HsString (fsLit "noSyntaxExpr"))
76 type SyntaxTable id = [(Name, SyntaxExpr id)]
77 -- ^ Currently used only for 'CmdTop' (sigh)
79 -- * Before the renamer, this list is 'noSyntaxTable'
81 -- * After the renamer, it takes the form @[(std_name, HsVar actual_name)]@
82 -- For example, for the 'return' op of a monad
84 -- * normal case: @(GHC.Base.return, HsVar GHC.Base.return)@
86 -- * with rebindable syntax: @(GHC.Base.return, return_22)@
87 -- where @return_22@ is whatever @return@ is in scope
89 -- * After the type checker, it takes the form @[(std_name, <expression>)]@
90 -- where @<expression>@ is the evidence for the method
92 noSyntaxTable :: SyntaxTable id
96 -------------------------
97 -- | A Haskell expression.
99 = HsVar id -- ^ variable
100 | HsIPVar (IPName id) -- ^ implicit parameter
101 | HsOverLit (HsOverLit id) -- ^ Overloaded literals
103 | HsLit HsLit -- ^ Simple (non-overloaded) literals
105 | HsLam (MatchGroup id) -- Currently always a single match
107 | HsApp (LHsExpr id) (LHsExpr id) -- Application
109 | HsKappa (MatchGroup id)
111 | HsKappaApp (LHsExpr id) (LHsExpr id)
113 -- Operator applications:
114 -- NB Bracketed ops such as (+) come out as Vars.
116 -- NB We need an expr for the operator in an OpApp/Section since
117 -- the typechecker may need to apply the operator to a few types.
119 | OpApp (LHsExpr id) -- left operand
120 (LHsExpr id) -- operator
121 Fixity -- Renamer adds fixity; bottom until then
122 (LHsExpr id) -- right operand
124 | NegApp (LHsExpr id) -- negated expr
125 (SyntaxExpr id) -- Name of 'negate'
127 | HsPar (LHsExpr id) -- parenthesised expr
129 | SectionL (LHsExpr id) -- operand
130 (LHsExpr id) -- operator
131 | SectionR (LHsExpr id) -- operator
132 (LHsExpr id) -- operand
134 | ExplicitTuple -- Used for explicit tuples and sections thereof
138 | HsCase (LHsExpr id)
141 | HsIf (Maybe (SyntaxExpr id)) -- cond function
142 -- Nothing => use the built-in 'if'
143 -- See Note [Rebindable if]
144 (LHsExpr id) -- predicate
145 (LHsExpr id) -- then part
146 (LHsExpr id) -- else part
148 | HsLet (HsLocalBinds id) -- let(rec)
151 | HsDo (HsStmtContext Name) -- The parameterisation is unimportant
152 -- because in this context we never use
153 -- the PatGuard or ParStmt variant
154 [LStmt id] -- "do":one or more stmts
155 PostTcType -- Type of the whole expression
157 | ExplicitList -- syntactic list
158 PostTcType -- Gives type of components of list
161 | ExplicitPArr -- syntactic parallel array: [:e1, ..., en:]
162 PostTcType -- type of elements of the parallel array
165 -- Record construction
166 | RecordCon (Located id) -- The constructor. After type checking
167 -- it's the dataConWrapId of the constructor
168 PostTcExpr -- Data con Id applied to type args
172 | RecordUpd (LHsExpr id)
174 -- (HsMatchGroup Id) -- Filled in by the type checker to be
175 -- -- a match that does the job
176 [DataCon] -- Filled in by the type checker to the
177 -- _non-empty_ list of DataCons that have
178 -- all the upd'd fields
179 [PostTcType] -- Argument types of *input* record type
180 [PostTcType] -- and *output* record type
181 -- For a type family, the arg types are of the *instance* tycon,
182 -- not the family tycon
184 | ExprWithTySig -- e :: type
188 | ExprWithTySigOut -- TRANSLATION
190 (LHsType Name) -- Retain the signature for
191 -- round-tripping purposes
193 | ArithSeq -- arithmetic sequence
197 | PArrSeq -- arith. sequence for parallel array
198 PostTcExpr -- [:e1..e2:] or [:e1, e2..e3:]
201 | HsSCC FastString -- "set cost centre" SCC pragma
202 (LHsExpr id) -- expr whose cost is to be measured
204 | HsCoreAnn FastString -- hdaume: core annotation
207 -----------------------------------------------------------
208 -- MetaHaskell Extensions
210 | HsBracket (HsBracket id)
212 | HsBracketOut (HsBracket Name) -- Output of the type checker is
214 [PendingSplice] -- renamed expression, plus
215 -- _typechecked_ splices to be
216 -- pasted back in by the desugarer
218 | HsSpliceE (HsSplice id)
220 | HsQuasiQuoteE (HsQuasiQuote id)
221 -- See Note [Quasi-quote overview] in TcSplice
223 -----------------------------------------------------------
224 -- Arrow notation extension
226 | HsProc (LPat id) -- arrow abstraction, proc
227 (LHsCmdTop id) -- body of the abstraction
228 -- always has an empty stack
230 -----------------------------------------------------------
231 -- Heterogeneous Metaprogramming extension
233 | HsHetMetBrak PostTcType (LHsExpr id) -- code type brackets
234 | HsHetMetEsc PostTcType PostTcType (LHsExpr id) -- code type escape
235 | HsHetMetCSP PostTcType (LHsExpr id) -- code type cross-stage persistence
237 ---------------------------------------
238 -- The following are commands, not expressions proper
240 | HsArrApp -- Arrow tail, or arrow application (f -< arg)
241 (LHsExpr id) -- arrow expression, f
242 (LHsExpr id) -- input expression, arg
243 PostTcType -- type of the arrow expressions f,
244 -- of the form a t t', where arg :: t
245 HsArrAppType -- higher-order (-<<) or first-order (-<)
246 Bool -- True => right-to-left (f -< arg)
247 -- False => left-to-right (arg >- f)
249 | HsArrForm -- Command formation, (| e cmd1 .. cmdn |)
250 (LHsExpr id) -- the operator
251 -- after type-checking, a type abstraction to be
252 -- applied to the type of the local environment tuple
253 (Maybe Fixity) -- fixity (filled in by the renamer), for forms that
254 -- were converted from OpApp's by the renamer
255 [LHsCmdTop id] -- argument commands
258 ---------------------------------------
259 -- Haskell program coverage (Hpc) Support
262 Int -- module-local tick number
263 [id] -- variables in scope
264 (LHsExpr id) -- sub-expression
267 Int -- module-local tick number for True
268 Int -- module-local tick number for False
269 (LHsExpr id) -- sub-expression
271 | HsTickPragma -- A pragma introduced tick
272 (FastString,(Int,Int),(Int,Int)) -- external span for this tick
275 ---------------------------------------
276 -- These constructors only appear temporarily in the parser.
277 -- The renamer translates them into the Right Thing.
279 | EWildPat -- wildcard
281 | EAsPat (Located id) -- as pattern
284 | EViewPat (LHsExpr id) -- view pattern
287 | ELazyPat (LHsExpr id) -- ~ pattern
289 | HsType (LHsType id) -- Explicit type argument; e.g f {| Int |} x y
291 ---------------------------------------
292 -- Finally, HsWrap appears only in typechecker output
294 | HsWrap HsWrapper -- TRANSLATION
296 deriving (Data, Typeable)
298 -- HsTupArg is used for tuple sections
299 -- (,a,) is represented by ExplicitTuple [Mising ty1, Present a, Missing ty3]
300 -- Which in turn stands for (\x:ty1 \y:ty2. (x,a,y))
302 = Present (LHsExpr id) -- The argument
303 | Missing PostTcType -- The argument is missing, but this is its type
304 deriving (Data, Typeable)
306 tupArgPresent :: HsTupArg id -> Bool
307 tupArgPresent (Present {}) = True
308 tupArgPresent (Missing {}) = False
310 type PendingSplice = (Name, LHsExpr Id) -- Typechecked splices, waiting to be
311 -- pasted back in by the desugarer
316 The rebindable syntax for 'if' is a bit special, because when
317 rebindable syntax is *off* we do not want to treat
319 as if it was an application (ifThenElse c t e). Why not?
320 Because we allow an 'if' to return *unboxed* results, thus
321 if blah then 3# else 4#
322 whereas that would not be possible using a all to a polymorphic function
323 (because you can't call a polymorphic function at an unboxed type).
325 So we use Nothing to mean "use the old built-in typing rule".
328 instance OutputableBndr id => Outputable (HsExpr id) where
329 ppr expr = pprExpr expr
333 -----------------------
334 -- pprExpr, pprLExpr, pprBinds call pprDeeper;
335 -- the underscore versions do not
336 pprLExpr :: OutputableBndr id => LHsExpr id -> SDoc
337 pprLExpr (L _ e) = pprExpr e
339 pprExpr :: OutputableBndr id => HsExpr id -> SDoc
340 pprExpr e | isAtomicHsExpr e || isQuietHsExpr e = ppr_expr e
341 | otherwise = pprDeeper (ppr_expr e)
343 isQuietHsExpr :: HsExpr id -> Bool
344 -- Parentheses do display something, but it gives little info and
345 -- if we go deeper when we go inside them then we get ugly things
347 isQuietHsExpr (HsPar _) = True
348 -- applications don't display anything themselves
349 isQuietHsExpr (HsApp _ _) = True
350 isQuietHsExpr (OpApp _ _ _ _) = True
351 isQuietHsExpr _ = False
353 pprBinds :: (OutputableBndr idL, OutputableBndr idR)
354 => HsLocalBindsLR idL idR -> SDoc
355 pprBinds b = pprDeeper (ppr b)
357 -----------------------
358 ppr_lexpr :: OutputableBndr id => LHsExpr id -> SDoc
359 ppr_lexpr e = ppr_expr (unLoc e)
361 ppr_expr :: OutputableBndr id => HsExpr id -> SDoc
362 ppr_expr (HsVar v) = pprHsVar v
363 ppr_expr (HsIPVar v) = ppr v
364 ppr_expr (HsLit lit) = ppr lit
365 ppr_expr (HsOverLit lit) = ppr lit
366 ppr_expr (HsPar e) = parens (ppr_lexpr e)
367 ppr_expr (HsHetMetBrak _ e) = ptext (sLit "<[") <> (ppr_lexpr e) <> ptext (sLit "]>")
368 ppr_expr (HsHetMetEsc _ _ e) = ptext (sLit "~~") <> (ppr_lexpr e)
369 ppr_expr (HsHetMetCSP _ e) = ptext (sLit "%%") <> (ppr_lexpr e)
371 ppr_expr (HsCoreAnn s e)
372 = vcat [ptext (sLit "HsCoreAnn") <+> ftext s, ppr_lexpr e]
374 ppr_expr (HsKappaApp e1 e2) = ppr_expr $ HsApp e1 e2
375 ppr_expr (HsKappa e) = ppr_expr $ HsLam e
376 ppr_expr (HsApp e1 e2)
377 = let (fun, args) = collect_args e1 [e2] in
378 hang (ppr_lexpr fun) 2 (sep (map pprParendExpr args))
380 collect_args (L _ (HsApp fun arg)) args = collect_args fun (arg:args)
381 collect_args fun args = (fun, args)
383 ppr_expr (OpApp e1 op _ e2)
385 HsVar v -> pp_infixly v
388 pp_e1 = pprDebugParendExpr e1 -- In debug mode, add parens
389 pp_e2 = pprDebugParendExpr e2 -- to make precedence clear
392 = hang (ppr op) 2 (sep [pp_e1, pp_e2])
395 = sep [nest 2 pp_e1, pprHsInfix v, nest 2 pp_e2]
397 ppr_expr (NegApp e _) = char '-' <+> pprDebugParendExpr e
399 ppr_expr (SectionL expr op)
401 HsVar v -> pp_infixly v
404 pp_expr = pprDebugParendExpr expr
406 pp_prefixly = hang (hsep [text " \\ x_ ->", ppr op])
407 4 (hsep [pp_expr, ptext (sLit "x_ )")])
408 pp_infixly v = (sep [pp_expr, pprHsInfix v])
410 ppr_expr (SectionR op expr)
412 HsVar v -> pp_infixly v
415 pp_expr = pprDebugParendExpr expr
417 pp_prefixly = hang (hsep [text "( \\ x_ ->", ppr op, ptext (sLit "x_")])
418 4 ((<>) pp_expr rparen)
420 = (sep [pprHsInfix v, pp_expr])
422 ppr_expr (ExplicitTuple exprs boxity)
423 = tupleParens boxity (fcat (ppr_tup_args exprs))
426 ppr_tup_args (Present e : es) = (ppr_lexpr e <> punc es) : ppr_tup_args es
427 ppr_tup_args (Missing _ : es) = punc es : ppr_tup_args es
429 punc (Present {} : _) = comma <> space
430 punc (Missing {} : _) = comma
433 --avoid using PatternSignatures for stage1 code portability
434 ppr_expr exprType@(HsLam matches)
435 = pprMatches (LambdaExpr `asTypeOf` idType exprType) matches
436 where idType :: HsExpr id -> HsMatchContext id; idType = undefined
438 ppr_expr exprType@(HsCase expr matches)
439 = sep [ sep [ptext (sLit "case"), nest 4 (ppr expr), ptext (sLit "of {")],
440 nest 2 (pprMatches (CaseAlt `asTypeOf` idType exprType) matches <+> char '}') ]
441 where idType :: HsExpr id -> HsMatchContext id; idType = undefined
443 ppr_expr (HsIf _ e1 e2 e3)
444 = sep [hsep [ptext (sLit "if"), nest 2 (ppr e1), ptext (sLit "then")],
449 -- special case: let ... in let ...
450 ppr_expr (HsLet binds expr@(L _ (HsLet _ _)))
451 = sep [hang (ptext (sLit "let")) 2 (hsep [pprBinds binds, ptext (sLit "in")]),
454 ppr_expr (HsLet binds expr)
455 = sep [hang (ptext (sLit "let")) 2 (pprBinds binds),
456 hang (ptext (sLit "in")) 2 (ppr expr)]
458 ppr_expr (HsDo do_or_list_comp stmts _) = pprDo do_or_list_comp stmts
460 ppr_expr (ExplicitList _ exprs)
461 = brackets (pprDeeperList fsep (punctuate comma (map ppr_lexpr exprs)))
463 ppr_expr (ExplicitPArr _ exprs)
464 = pa_brackets (pprDeeperList fsep (punctuate comma (map ppr_lexpr exprs)))
466 ppr_expr (RecordCon con_id _ rbinds)
467 = hang (ppr con_id) 2 (ppr rbinds)
469 ppr_expr (RecordUpd aexp rbinds _ _ _)
470 = hang (pprParendExpr aexp) 2 (ppr rbinds)
472 ppr_expr (ExprWithTySig expr sig)
473 = hang (nest 2 (ppr_lexpr expr) <+> dcolon)
475 ppr_expr (ExprWithTySigOut expr sig)
476 = hang (nest 2 (ppr_lexpr expr) <+> dcolon)
479 ppr_expr (ArithSeq _ info) = brackets (ppr info)
480 ppr_expr (PArrSeq _ info) = pa_brackets (ppr info)
482 ppr_expr EWildPat = char '_'
483 ppr_expr (ELazyPat e) = char '~' <> pprParendExpr e
484 ppr_expr (EAsPat v e) = ppr v <> char '@' <> pprParendExpr e
485 ppr_expr (EViewPat p e) = ppr p <+> ptext (sLit "->") <+> ppr e
487 ppr_expr (HsSCC lbl expr)
488 = sep [ ptext (sLit "_scc_") <+> doubleQuotes (ftext lbl),
491 ppr_expr (HsWrap co_fn e) = pprHsWrapper (pprExpr e) co_fn
492 ppr_expr (HsType id) = ppr id
494 ppr_expr (HsSpliceE s) = pprSplice s
495 ppr_expr (HsBracket b) = pprHsBracket b
496 ppr_expr (HsBracketOut e []) = ppr e
497 ppr_expr (HsBracketOut e ps) = ppr e $$ ptext (sLit "pending") <+> ppr ps
498 ppr_expr (HsQuasiQuoteE qq) = ppr qq
500 ppr_expr (HsProc pat (L _ (HsCmdTop cmd _ _ _)))
501 = hsep [ptext (sLit "proc"), ppr pat, ptext (sLit "->"), ppr cmd]
503 ppr_expr (HsTick tickId vars exp)
504 = pprTicks (ppr exp) $
505 hcat [ptext (sLit "tick<"),
508 hsep (map pprHsVar vars),
511 ppr_expr (HsBinTick tickIdTrue tickIdFalse exp)
512 = pprTicks (ppr exp) $
513 hcat [ptext (sLit "bintick<"),
518 ppr exp,ptext (sLit ")")]
519 ppr_expr (HsTickPragma externalSrcLoc exp)
520 = pprTicks (ppr exp) $
521 hcat [ptext (sLit "tickpragma<"),
527 ppr_expr (HsArrApp arrow arg _ HsFirstOrderApp True)
528 = hsep [ppr_lexpr arrow, ptext (sLit "-<"), ppr_lexpr arg]
529 ppr_expr (HsArrApp arrow arg _ HsFirstOrderApp False)
530 = hsep [ppr_lexpr arg, ptext (sLit ">-"), ppr_lexpr arrow]
531 ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp True)
532 = hsep [ppr_lexpr arrow, ptext (sLit "-<<"), ppr_lexpr arg]
533 ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp False)
534 = hsep [ppr_lexpr arg, ptext (sLit ">>-"), ppr_lexpr arrow]
536 ppr_expr (HsArrForm (L _ (HsVar v)) (Just _) [arg1, arg2])
537 = sep [pprCmdArg (unLoc arg1), hsep [pprHsInfix v, pprCmdArg (unLoc arg2)]]
538 ppr_expr (HsArrForm op _ args)
539 = hang (ptext (sLit "(|") <> ppr_lexpr op)
540 4 (sep (map (pprCmdArg.unLoc) args) <> ptext (sLit "|)"))
542 pprCmdArg :: OutputableBndr id => HsCmdTop id -> SDoc
543 pprCmdArg (HsCmdTop cmd@(L _ (HsArrForm _ Nothing [])) _ _ _)
545 pprCmdArg (HsCmdTop cmd _ _ _)
546 = parens (ppr_lexpr cmd)
548 instance OutputableBndr id => Outputable (HsCmdTop id) where
551 -- add parallel array brackets around a document
553 pa_brackets :: SDoc -> SDoc
554 pa_brackets p = ptext (sLit "[:") <> p <> ptext (sLit ":]")
557 HsSyn records exactly where the user put parens, with HsPar.
558 So generally speaking we print without adding any parens.
559 However, some code is internally generated, and in some places
560 parens are absolutely required; so for these places we use
561 pprParendExpr (but don't print double parens of course).
563 For operator applications we don't add parens, because the oprerator
564 fixities should do the job, except in debug mode (-dppr-debug) so we
565 can see the structure of the parse tree.
568 pprDebugParendExpr :: OutputableBndr id => LHsExpr id -> SDoc
569 pprDebugParendExpr expr
570 = getPprStyle (\sty ->
571 if debugStyle sty then pprParendExpr expr
574 pprParendExpr :: OutputableBndr id => LHsExpr id -> SDoc
577 pp_as_was = pprLExpr expr
578 -- Using pprLExpr makes sure that we go 'deeper'
579 -- I think that is usually (always?) right
582 ArithSeq {} -> pp_as_was
583 PArrSeq {} -> pp_as_was
584 HsLit {} -> pp_as_was
585 HsOverLit {} -> pp_as_was
586 HsVar {} -> pp_as_was
587 HsIPVar {} -> pp_as_was
588 ExplicitTuple {} -> pp_as_was
589 ExplicitList {} -> pp_as_was
590 ExplicitPArr {} -> pp_as_was
591 HsPar {} -> pp_as_was
592 HsBracket {} -> pp_as_was
593 HsBracketOut _ [] -> pp_as_was
595 | isListCompExpr sc -> pp_as_was
596 _ -> parens pp_as_was
598 isAtomicHsExpr :: HsExpr id -> Bool -- A single token
599 isAtomicHsExpr (HsVar {}) = True
600 isAtomicHsExpr (HsLit {}) = True
601 isAtomicHsExpr (HsOverLit {}) = True
602 isAtomicHsExpr (HsIPVar {}) = True
603 isAtomicHsExpr (HsWrap _ e) = isAtomicHsExpr e
604 isAtomicHsExpr (HsPar e) = isAtomicHsExpr (unLoc e)
605 isAtomicHsExpr _ = False
608 %************************************************************************
610 \subsection{Commands (in arrow abstractions)}
612 %************************************************************************
614 We re-use HsExpr to represent these.
617 type HsCmd id = HsExpr id
619 type LHsCmd id = LHsExpr id
621 data HsArrAppType = HsHigherOrderApp | HsFirstOrderApp
622 deriving (Data, Typeable)
625 The legal constructors for commands are:
627 = HsArrApp ... -- as above
629 | HsArrForm ... -- as above
634 | HsLam (Match id) -- kappa
636 -- the renamer turns this one into HsArrForm
637 | OpApp (HsExpr id) -- left operand
638 (HsCmd id) -- operator
639 Fixity -- Renamer adds fixity; bottom until then
640 (HsCmd id) -- right operand
642 | HsPar (HsCmd id) -- parenthesised command
645 [Match id] -- bodies are HsCmd's
648 | HsIf (Maybe (SyntaxExpr id)) -- cond function
649 (HsExpr id) -- predicate
650 (HsCmd id) -- then part
651 (HsCmd id) -- else part
654 | HsLet (HsLocalBinds id) -- let(rec)
657 | HsDo (HsStmtContext Name) -- The parameterisation is unimportant
658 -- because in this context we never use
659 -- the PatGuard or ParStmt variant
660 [Stmt id] -- HsExpr's are really HsCmd's
661 PostTcType -- Type of the whole expression
664 Top-level command, introducing a new arrow.
665 This may occur inside a proc (where the stack is empty) or as an
666 argument of a command-forming operator.
669 type LHsCmdTop id = Located (HsCmdTop id)
672 = HsCmdTop (LHsCmd id)
673 [PostTcType] -- types of inputs on the command's stack
674 PostTcType -- return type of the command
675 (SyntaxTable id) -- after type checking:
676 -- names used in the command's desugaring
677 deriving (Data, Typeable)
680 %************************************************************************
682 \subsection{Record binds}
684 %************************************************************************
687 type HsRecordBinds id = HsRecFields id (LHsExpr id)
692 %************************************************************************
694 \subsection{@Match@, @GRHSs@, and @GRHS@ datatypes}
696 %************************************************************************
698 @Match@es are sets of pattern bindings and right hand sides for
699 functions, patterns or case branches. For example, if a function @g@
705 then \tr{g} has two @Match@es: @(x,y) = y@ and @((x:ys),y) = y+1@.
707 It is always the case that each element of an @[Match]@ list has the
708 same number of @pats@s inside it. This corresponds to saying that
709 a function defined by pattern matching must have the same number of
710 patterns in each equation.
715 [LMatch id] -- The alternatives
716 PostTcType -- The type is the type of the entire group
717 -- t1 -> ... -> tn -> tr
718 -- where there are n patterns
719 deriving (Data, Typeable)
721 type LMatch id = Located (Match id)
725 [LPat id] -- The patterns
726 (Maybe (LHsType id)) -- A type signature for the result of the match
727 -- Nothing after typechecking
729 deriving (Data, Typeable)
731 isEmptyMatchGroup :: MatchGroup id -> Bool
732 isEmptyMatchGroup (MatchGroup ms _) = null ms
734 matchGroupArity :: MatchGroup id -> Arity
735 matchGroupArity (MatchGroup [] _)
736 = panic "matchGroupArity" -- Precondition: MatchGroup is non-empty
737 matchGroupArity (MatchGroup (match:matches) _)
738 = ASSERT( all ((== n_pats) . length . hsLMatchPats) matches )
739 -- Assertion just checks that all the matches have the same number of pats
742 n_pats = length (hsLMatchPats match)
744 hsLMatchPats :: LMatch id -> [LPat id]
745 hsLMatchPats (L _ (Match pats _ _)) = pats
747 -- | GRHSs are used both for pattern bindings and for Matches
750 grhssGRHSs :: [LGRHS id], -- ^ Guarded RHSs
751 grhssLocalBinds :: (HsLocalBinds id) -- ^ The where clause
752 } deriving (Data, Typeable)
754 type LGRHS id = Located (GRHS id)
756 -- | Guarded Right Hand Side.
757 data GRHS id = GRHS [LStmt id] -- Guards
758 (LHsExpr id) -- Right hand side
759 deriving (Data, Typeable)
762 We know the list must have at least one @Match@ in it.
765 pprMatches :: (OutputableBndr idL, OutputableBndr idR) => HsMatchContext idL -> MatchGroup idR -> SDoc
766 pprMatches ctxt (MatchGroup matches _)
767 = vcat (map (pprMatch ctxt) (map unLoc matches))
768 -- Don't print the type; it's only a place-holder before typechecking
770 -- Exported to HsBinds, which can't see the defn of HsMatchContext
771 pprFunBind :: (OutputableBndr idL, OutputableBndr idR) => idL -> Bool -> MatchGroup idR -> SDoc
772 pprFunBind fun inf matches = pprMatches (FunRhs fun inf) matches
774 -- Exported to HsBinds, which can't see the defn of HsMatchContext
775 pprPatBind :: (OutputableBndr bndr, OutputableBndr id)
776 => LPat bndr -> GRHSs id -> SDoc
777 pprPatBind pat ty@(grhss)
778 = sep [ppr pat, nest 2 (pprGRHSs (PatBindRhs `asTypeOf` idType ty) grhss)]
779 --avoid using PatternSignatures for stage1 code portability
780 where idType :: GRHSs id -> HsMatchContext id; idType = undefined
783 pprMatch :: (OutputableBndr idL, OutputableBndr idR) => HsMatchContext idL -> Match idR -> SDoc
784 pprMatch ctxt (Match pats maybe_ty grhss)
785 = sep [ sep (herald : map (nest 2 . pprParendLPat) other_pats)
786 , nest 2 ppr_maybe_ty
787 , nest 2 (pprGRHSs ctxt grhss) ]
792 | not is_infix -> (ppr fun, pats)
794 -- Not pprBndr; the AbsBinds will
795 -- have printed the signature
797 | null pats2 -> (pp_infix, [])
800 | otherwise -> (parens pp_infix, pats2)
803 pp_infix = pprParendLPat pat1 <+> ppr fun <+> pprParendLPat pat2
805 LambdaExpr -> (char '\\', pats)
807 _ -> ASSERT( null pats1 )
808 (ppr pat1, []) -- No parens around the single pat
812 ppr_maybe_ty = case maybe_ty of
813 Just ty -> dcolon <+> ppr ty
817 pprGRHSs :: (OutputableBndr idL, OutputableBndr idR)
818 => HsMatchContext idL -> GRHSs idR -> SDoc
819 pprGRHSs ctxt (GRHSs grhss binds)
820 = vcat (map (pprGRHS ctxt . unLoc) grhss)
821 $$ ppUnless (isEmptyLocalBinds binds)
822 (text "where" $$ nest 4 (pprBinds binds))
824 pprGRHS :: (OutputableBndr idL, OutputableBndr idR)
825 => HsMatchContext idL -> GRHS idR -> SDoc
827 pprGRHS ctxt (GRHS [] expr)
830 pprGRHS ctxt (GRHS guards expr)
831 = sep [char '|' <+> interpp'SP guards, pp_rhs ctxt expr]
833 pp_rhs :: OutputableBndr idR => HsMatchContext idL -> LHsExpr idR -> SDoc
834 pp_rhs ctxt rhs = matchSeparator ctxt <+> pprDeeper (ppr rhs)
837 %************************************************************************
839 \subsection{Do stmts and list comprehensions}
841 %************************************************************************
844 type LStmt id = Located (StmtLR id id)
845 type LStmtLR idL idR = Located (StmtLR idL idR)
847 type Stmt id = StmtLR id id
849 -- The SyntaxExprs in here are used *only* for do-notation and monad
850 -- comprehensions, which have rebindable syntax. Otherwise they are unused.
852 = LastStmt -- Always the last Stmt in ListComp, MonadComp, PArrComp,
853 -- and (after the renamer) DoExpr, MDoExpr
854 -- Not used for GhciStmt, PatGuard, which scope over other stuff
856 (SyntaxExpr idR) -- The return operator, used only for MonadComp
857 -- For ListComp, PArrComp, we use the baked-in 'return'
858 -- For DoExpr, MDoExpr, we don't appply a 'return' at all
859 -- See Note [Monad Comprehensions]
860 | BindStmt (LPat idL)
862 (SyntaxExpr idR) -- The (>>=) operator; see Note [The type of bind]
863 (SyntaxExpr idR) -- The fail operator
864 -- The fail operator is noSyntaxExpr
865 -- if the pattern match can't fail
867 | ExprStmt (LHsExpr idR) -- See Note [ExprStmt]
868 (SyntaxExpr idR) -- The (>>) operator
869 (SyntaxExpr idR) -- The `guard` operator; used only in MonadComp
870 -- See notes [Monad Comprehensions]
871 PostTcType -- Element type of the RHS (used for arrows)
873 | LetStmt (HsLocalBindsLR idL idR)
875 -- ParStmts only occur in a list/monad comprehension
876 | ParStmt [([LStmt idL], [idR])]
877 (SyntaxExpr idR) -- Polymorphic `mzip` for monad comprehensions
878 (SyntaxExpr idR) -- The `>>=` operator
879 (SyntaxExpr idR) -- Polymorphic `return` operator
880 -- with type (forall a. a -> m a)
881 -- See notes [Monad Comprehensions]
882 -- After renaming, the ids are the binders
883 -- bound by the stmts and used after themp
886 trS_form :: TransForm,
887 trS_stmts :: [LStmt idL], -- Stmts to the *left* of the 'group'
888 -- which generates the tuples to be grouped
890 trS_bndrs :: [(idR, idR)], -- See Note [TransStmt binder map]
892 trS_using :: LHsExpr idR,
893 trS_by :: Maybe (LHsExpr idR), -- "by e" (optional)
894 -- Invariant: if trS_form = GroupBy, then grp_by = Just e
896 trS_ret :: SyntaxExpr idR, -- The monomorphic 'return' function for
897 -- the inner monad comprehensions
898 trS_bind :: SyntaxExpr idR, -- The '(>>=)' operator
899 trS_fmap :: SyntaxExpr idR -- The polymorphic 'fmap' function for desugaring
900 -- Only for 'group' forms
901 } -- See Note [Monad Comprehensions]
903 -- Recursive statement (see Note [How RecStmt works] below)
905 { recS_stmts :: [LStmtLR idL idR]
907 -- The next two fields are only valid after renaming
908 , recS_later_ids :: [idR] -- The ids are a subset of the variables bound by the
909 -- stmts that are used in stmts that follow the RecStmt
911 , recS_rec_ids :: [idR] -- Ditto, but these variables are the "recursive" ones,
912 -- that are used before they are bound in the stmts of
914 -- An Id can be in both groups
915 -- Both sets of Ids are (now) treated monomorphically
916 -- See Note [How RecStmt works] for why they are separate
919 , recS_bind_fn :: SyntaxExpr idR -- The bind function
920 , recS_ret_fn :: SyntaxExpr idR -- The return function
921 , recS_mfix_fn :: SyntaxExpr idR -- The mfix function
923 -- These fields are only valid after typechecking
924 , recS_rec_rets :: [PostTcExpr] -- These expressions correspond 1-to-1 with
925 -- recS_rec_ids, and are the
926 -- expressions that should be returned by
928 -- They may not quite be the Ids themselves,
929 -- because the Id may be *polymorphic*, but
930 -- the returned thing has to be *monomorphic*,
931 -- so they may be type applications
933 , recS_ret_ty :: PostTcType -- The type of of do { stmts; return (a,b,c) }
934 -- With rebindable syntax the type might not
935 -- be quite as simple as (m (tya, tyb, tyc)).
937 deriving (Data, Typeable)
939 data TransForm -- The 'f' below is the 'using' function, 'e' is the by function
940 = ThenForm -- then f or then f by e
941 | GroupFormU -- group using f or group using f by e
942 | GroupFormB -- group by e
943 -- In the GroupByFormB, trS_using is filled in with
944 -- 'groupWith' (list comprehensions) or
945 -- 'groupM' (monad comprehensions)
946 deriving (Data, Typeable)
949 Note [The type of bind in Stmts]
950 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
951 Some Stmts, notably BindStmt, keep the (>>=) bind operator.
952 We do NOT assume that it has type
953 (>>=) :: m a -> (a -> m b) -> m b
954 In some cases (see Trac #303, #1537) it might have a more
956 (>>=) :: m i j a -> (a -> m j k b) -> m i k b
957 So we must be careful not to make assumptions about the type.
958 In particular, the monad may not be uniform throughout.
960 Note [TransStmt binder map]
961 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
962 The [(idR,idR)] in a TransStmt behaves as follows:
964 * Before renaming: []
967 [ (x27,x27), ..., (z35,z35) ]
968 These are the variables
969 bound by the stmts to the left of the 'group'
970 and used either in the 'by' clause,
971 or in the stmts following the 'group'
972 Each item is a pair of identical variables.
974 * After typechecking:
975 [ (x27:Int, x27:[Int]), ..., (z35:Bool, z35:[Bool]) ]
976 Each pair has the same unique, but different *types*.
980 ExprStmts are a bit tricky, because what they mean
981 depends on the context. Consider the following contexts:
983 A do expression of type (m res_ty)
984 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
985 * ExprStmt E any_ty: do { ....; E; ... }
987 Translation: E >> ...
989 A list comprehensions of type [elt_ty]
990 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
991 * ExprStmt E Bool: [ .. | .... E ]
993 [ .. | .... | ..., E | ... ]
995 Translation: if E then fail else ...
997 A guard list, guarding a RHS of type rhs_ty
998 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
999 * ExprStmt E Bool: f x | ..., E, ... = ...rhs...
1001 Translation: if E then fail else ...
1003 A monad comprehension of type (m res_ty)
1004 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1005 * ExprStmt E Bool: [ .. | .... E ]
1007 Translation: guard E >> ...
1009 Array comprehensions are handled like list comprehensions.
1011 Note [How RecStmt works]
1012 ~~~~~~~~~~~~~~~~~~~~~~~~
1014 HsDo [ BindStmt x ex
1016 , RecStmt { recS_rec_ids = [a, c]
1017 , recS_stmts = [ BindStmt b (return (a,c))
1018 , LetStmt a = ...b...
1020 , recS_later_ids = [a, b]
1024 Here, the RecStmt binds a,b,c; but
1025 - Only a,b are used in the stmts *following* the RecStmt,
1026 - Only a,c are used in the stmts *inside* the RecStmt
1027 *before* their bindings
1029 Why do we need *both* rec_ids and later_ids? For monads they could be
1030 combined into a single set of variables, but not for arrows. That
1031 follows from the types of the respective feedback operators:
1033 mfix :: MonadFix m => (a -> m a) -> m a
1034 loop :: ArrowLoop a => a (b,d) (c,d) -> a b c
1036 * For mfix, the 'a' covers the union of the later_ids and the rec_ids
1037 * For 'loop', 'c' is the later_ids and 'd' is the rec_ids
1039 Note [Typing a RecStmt]
1040 ~~~~~~~~~~~~~~~~~~~~~~~
1041 A (RecStmt stmts) types as if you had written
1043 (v1,..,vn, _, ..., _) <- mfix (\~(_, ..., _, r1, ..., rm) ->
1045 ; return (v1,..vn, r1, ..., rm) })
1047 where v1..vn are the later_ids
1048 r1..rm are the rec_ids
1050 Note [Monad Comprehensions]
1051 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
1052 Monad comprehensions require separate functions like 'return' and
1053 '>>=' for desugaring. These functions are stored in the statements
1054 used in monad comprehensions. For example, the 'return' of the 'LastStmt'
1055 expression is used to lift the body of the monad comprehension:
1059 stmts >>= \bndrs -> return body
1061 In transform and grouping statements ('then ..' and 'then group ..') the
1062 'return' function is required for nested monad comprehensions, for example:
1064 [ body | stmts, then f, rest ]
1066 f [ env | stmts ] >>= \bndrs -> [ body | rest ]
1068 ExprStmts require the 'Control.Monad.guard' function for boolean
1071 [ body | exp, stmts ]
1073 guard exp >> [ body | stmts ]
1075 Grouping/parallel statements require the 'Control.Monad.Group.groupM' and
1076 'Control.Monad.Zip.mzip' functions:
1078 [ body | stmts, then group by e, rest]
1080 groupM [ body | stmts ] >>= \bndrs -> [ body | rest ]
1082 [ body | stmts1 | stmts2 | .. ]
1084 mzip stmts1 (mzip stmts2 (..)) >>= \(bndrs1, (bndrs2, ..)) -> return body
1086 In any other context than 'MonadComp', the fields for most of these
1087 'SyntaxExpr's stay bottom.
1091 instance (OutputableBndr idL, OutputableBndr idR) => Outputable (StmtLR idL idR) where
1092 ppr stmt = pprStmt stmt
1094 pprStmt :: (OutputableBndr idL, OutputableBndr idR) => (StmtLR idL idR) -> SDoc
1095 pprStmt (LastStmt expr _) = ifPprDebug (ptext (sLit "[last]")) <+> ppr expr
1096 pprStmt (BindStmt pat expr _ _) = hsep [ppr pat, ptext (sLit "<-"), ppr expr]
1097 pprStmt (LetStmt binds) = hsep [ptext (sLit "let"), pprBinds binds]
1098 pprStmt (ExprStmt expr _ _ _) = ppr expr
1099 pprStmt (ParStmt stmtss _ _ _) = hsep (map doStmts stmtss)
1100 where doStmts stmts = ptext (sLit "| ") <> ppr stmts
1102 pprStmt (TransStmt { trS_stmts = stmts, trS_by = by, trS_using = using, trS_form = form })
1103 = sep (ppr_lc_stmts stmts ++ [pprTransStmt by using form])
1105 pprStmt (RecStmt { recS_stmts = segment, recS_rec_ids = rec_ids
1106 , recS_later_ids = later_ids })
1107 = ptext (sLit "rec") <+>
1108 vcat [ braces (vcat (map ppr segment))
1109 , ifPprDebug (vcat [ ptext (sLit "rec_ids=") <> ppr rec_ids
1110 , ptext (sLit "later_ids=") <> ppr later_ids])]
1112 pprTransformStmt :: OutputableBndr id => [id] -> LHsExpr id -> Maybe (LHsExpr id) -> SDoc
1113 pprTransformStmt bndrs using by
1114 = sep [ ptext (sLit "then") <+> ifPprDebug (braces (ppr bndrs))
1115 , nest 2 (ppr using)
1116 , nest 2 (pprBy by)]
1118 pprTransStmt :: OutputableBndr id => Maybe (LHsExpr id)
1119 -> LHsExpr id -> TransForm
1121 pprTransStmt by using ThenForm
1122 = sep [ ptext (sLit "then"), nest 2 (ppr using), nest 2 (pprBy by)]
1123 pprTransStmt by _ GroupFormB
1124 = sep [ ptext (sLit "then group"), nest 2 (pprBy by) ]
1125 pprTransStmt by using GroupFormU
1126 = sep [ ptext (sLit "then group"), nest 2 (pprBy by), nest 2 (ptext (sLit "using") <+> ppr using)]
1128 pprBy :: OutputableBndr id => Maybe (LHsExpr id) -> SDoc
1129 pprBy Nothing = empty
1130 pprBy (Just e) = ptext (sLit "by") <+> ppr e
1132 pprDo :: OutputableBndr id => HsStmtContext any -> [LStmt id] -> SDoc
1133 pprDo DoExpr stmts = ptext (sLit "do") <+> ppr_do_stmts stmts
1134 pprDo GhciStmt stmts = ptext (sLit "do") <+> ppr_do_stmts stmts
1135 pprDo ArrowExpr stmts = ptext (sLit "do") <+> ppr_do_stmts stmts
1136 pprDo MDoExpr stmts = ptext (sLit "mdo") <+> ppr_do_stmts stmts
1137 pprDo ListComp stmts = brackets $ pprComp stmts
1138 pprDo PArrComp stmts = pa_brackets $ pprComp stmts
1139 pprDo MonadComp stmts = brackets $ pprComp stmts
1140 pprDo _ _ = panic "pprDo" -- PatGuard, ParStmtCxt
1142 ppr_do_stmts :: OutputableBndr id => [LStmt id] -> SDoc
1143 -- Print a bunch of do stmts, with explicit braces and semicolons,
1144 -- so that we are not vulnerable to layout bugs
1146 = lbrace <+> pprDeeperList vcat (punctuate semi (map ppr stmts))
1149 ppr_lc_stmts :: OutputableBndr id => [LStmt id] -> [SDoc]
1150 ppr_lc_stmts stmts = [ppr s <> comma | s <- stmts]
1152 pprComp :: OutputableBndr id => [LStmt id] -> SDoc
1153 pprComp quals -- Prints: body | qual1, ..., qualn
1155 , L _ (LastStmt body _) <- last quals
1156 = hang (ppr body <+> char '|') 2 (interpp'SP (dropTail 1 quals))
1158 = pprPanic "pprComp" (interpp'SP quals)
1161 %************************************************************************
1163 Template Haskell quotation brackets
1165 %************************************************************************
1168 data HsSplice id = HsSplice -- $z or $(f 4)
1169 id -- The id is just a unique name to
1170 (LHsExpr id) -- identify this splice point
1171 deriving (Data, Typeable)
1173 instance OutputableBndr id => Outputable (HsSplice id) where
1176 pprSplice :: OutputableBndr id => HsSplice id -> SDoc
1177 pprSplice (HsSplice n e)
1178 = char '$' <> ifPprDebug (brackets (ppr n)) <> eDoc
1180 -- We use pprLExpr to match pprParendExpr:
1181 -- Using pprLExpr makes sure that we go 'deeper'
1182 -- I think that is usually (always?) right
1183 pp_as_was = pprLExpr e
1184 eDoc = case unLoc e of
1185 HsPar _ -> pp_as_was
1186 HsVar _ -> pp_as_was
1187 _ -> parens pp_as_was
1189 data HsBracket id = ExpBr (LHsExpr id) -- [| expr |]
1190 | PatBr (LPat id) -- [p| pat |]
1191 | DecBrL [LHsDecl id] -- [d| decls |]; result of parser
1192 | DecBrG (HsGroup id) -- [d| decls |]; result of renamer
1193 | TypBr (LHsType id) -- [t| type |]
1194 | VarBr id -- 'x, ''T
1195 deriving (Data, Typeable)
1197 instance OutputableBndr id => Outputable (HsBracket id) where
1201 pprHsBracket :: OutputableBndr id => HsBracket id -> SDoc
1202 pprHsBracket (ExpBr e) = thBrackets empty (ppr e)
1203 pprHsBracket (PatBr p) = thBrackets (char 'p') (ppr p)
1204 pprHsBracket (DecBrG gp) = thBrackets (char 'd') (ppr gp)
1205 pprHsBracket (DecBrL ds) = thBrackets (char 'd') (vcat (map ppr ds))
1206 pprHsBracket (TypBr t) = thBrackets (char 't') (ppr t)
1207 pprHsBracket (VarBr n) = char '\'' <> ppr n
1208 -- Infelicity: can't show ' vs '', because
1209 -- we can't ask n what its OccName is, because the
1210 -- pretty-printer for HsExpr doesn't ask for NamedThings
1211 -- But the pretty-printer for names will show the OccName class
1213 thBrackets :: SDoc -> SDoc -> SDoc
1214 thBrackets pp_kind pp_body = char '[' <> pp_kind <> char '|' <+>
1215 pp_body <+> ptext (sLit "|]")
1218 %************************************************************************
1220 \subsection{Enumerations and list comprehensions}
1222 %************************************************************************
1225 data ArithSeqInfo id
1227 | FromThen (LHsExpr id)
1229 | FromTo (LHsExpr id)
1231 | FromThenTo (LHsExpr id)
1234 deriving (Data, Typeable)
1238 instance OutputableBndr id => Outputable (ArithSeqInfo id) where
1239 ppr (From e1) = hcat [ppr e1, pp_dotdot]
1240 ppr (FromThen e1 e2) = hcat [ppr e1, comma, space, ppr e2, pp_dotdot]
1241 ppr (FromTo e1 e3) = hcat [ppr e1, pp_dotdot, ppr e3]
1242 ppr (FromThenTo e1 e2 e3)
1243 = hcat [ppr e1, comma, space, ppr e2, pp_dotdot, ppr e3]
1246 pp_dotdot = ptext (sLit " .. ")
1250 %************************************************************************
1252 \subsection{HsMatchCtxt}
1254 %************************************************************************
1257 data HsMatchContext id -- Context of a Match
1258 = FunRhs id Bool -- Function binding for f; True <=> written infix
1259 | LambdaExpr -- Patterns of a lambda
1260 | CaseAlt -- Patterns and guards on a case alternative
1261 | ProcExpr -- Patterns of a proc
1262 | PatBindRhs -- A pattern binding eg [y] <- e = e
1264 | RecUpd -- Record update [used only in DsExpr to
1265 -- tell matchWrapper what sort of
1266 -- runtime error message to generate]
1268 | StmtCtxt (HsStmtContext id) -- Pattern of a do-stmt, list comprehension,
1269 -- pattern guard, etc
1271 | ThPatQuote -- A Template Haskell pattern quotation [p| (a,b) |]
1272 deriving (Data, Typeable)
1274 data HsStmtContext id
1277 | PArrComp -- Parallel array comprehension
1279 | DoExpr -- do { ... }
1280 | MDoExpr -- mdo { ... } ie recursive do-expression
1281 | ArrowExpr -- do-notation in an arrow-command context
1283 | GhciStmt -- A command-line Stmt in GHCi pat <- rhs
1284 | PatGuard (HsMatchContext id) -- Pattern guard for specified thing
1285 | ParStmtCtxt (HsStmtContext id) -- A branch of a parallel stmt
1286 | TransStmtCtxt (HsStmtContext id) -- A branch of a transform stmt
1287 deriving (Data, Typeable)
1291 isListCompExpr :: HsStmtContext id -> Bool
1292 -- Uses syntax [ e | quals ]
1293 isListCompExpr ListComp = True
1294 isListCompExpr PArrComp = True
1295 isListCompExpr MonadComp = True
1296 isListCompExpr (ParStmtCtxt c) = isListCompExpr c
1297 isListCompExpr (TransStmtCtxt c) = isListCompExpr c
1298 isListCompExpr _ = False
1300 isMonadCompExpr :: HsStmtContext id -> Bool
1301 isMonadCompExpr MonadComp = True
1302 isMonadCompExpr (ParStmtCtxt ctxt) = isMonadCompExpr ctxt
1303 isMonadCompExpr (TransStmtCtxt ctxt) = isMonadCompExpr ctxt
1304 isMonadCompExpr _ = False
1308 matchSeparator :: HsMatchContext id -> SDoc
1309 matchSeparator (FunRhs {}) = ptext (sLit "=")
1310 matchSeparator CaseAlt = ptext (sLit "->")
1311 matchSeparator LambdaExpr = ptext (sLit "->")
1312 matchSeparator ProcExpr = ptext (sLit "->")
1313 matchSeparator PatBindRhs = ptext (sLit "=")
1314 matchSeparator (StmtCtxt _) = ptext (sLit "<-")
1315 matchSeparator RecUpd = panic "unused"
1316 matchSeparator ThPatQuote = panic "unused"
1320 pprMatchContext :: Outputable id => HsMatchContext id -> SDoc
1321 pprMatchContext ctxt
1322 | want_an ctxt = ptext (sLit "an") <+> pprMatchContextNoun ctxt
1323 | otherwise = ptext (sLit "a") <+> pprMatchContextNoun ctxt
1325 want_an (FunRhs {}) = True -- Use "an" in front
1326 want_an ProcExpr = True
1329 pprMatchContextNoun :: Outputable id => HsMatchContext id -> SDoc
1330 pprMatchContextNoun (FunRhs fun _) = ptext (sLit "equation for")
1331 <+> quotes (ppr fun)
1332 pprMatchContextNoun CaseAlt = ptext (sLit "case alternative")
1333 pprMatchContextNoun RecUpd = ptext (sLit "record-update construct")
1334 pprMatchContextNoun ThPatQuote = ptext (sLit "Template Haskell pattern quotation")
1335 pprMatchContextNoun PatBindRhs = ptext (sLit "pattern binding")
1336 pprMatchContextNoun LambdaExpr = ptext (sLit "lambda abstraction")
1337 pprMatchContextNoun ProcExpr = ptext (sLit "arrow abstraction")
1338 pprMatchContextNoun (StmtCtxt ctxt) = ptext (sLit "pattern binding in")
1339 $$ pprStmtContext ctxt
1342 pprAStmtContext, pprStmtContext :: Outputable id => HsStmtContext id -> SDoc
1343 pprAStmtContext ctxt = article <+> pprStmtContext ctxt
1345 pp_an = ptext (sLit "an")
1346 pp_a = ptext (sLit "a")
1347 article = case ctxt of
1355 pprStmtContext GhciStmt = ptext (sLit "interactive GHCi command")
1356 pprStmtContext DoExpr = ptext (sLit "'do' block")
1357 pprStmtContext MDoExpr = ptext (sLit "'mdo' block")
1358 pprStmtContext ArrowExpr = ptext (sLit "'do' block in an arrow command")
1359 pprStmtContext ListComp = ptext (sLit "list comprehension")
1360 pprStmtContext MonadComp = ptext (sLit "monad comprehension")
1361 pprStmtContext PArrComp = ptext (sLit "array comprehension")
1362 pprStmtContext (PatGuard ctxt) = ptext (sLit "pattern guard for") $$ pprMatchContext ctxt
1364 -- Drop the inner contexts when reporting errors, else we get
1365 -- Unexpected transform statement
1366 -- in a transformed branch of
1367 -- transformed branch of
1368 -- transformed branch of monad comprehension
1369 pprStmtContext (ParStmtCtxt c)
1370 | opt_PprStyle_Debug = sep [ptext (sLit "parallel branch of"), pprAStmtContext c]
1371 | otherwise = pprStmtContext c
1372 pprStmtContext (TransStmtCtxt c)
1373 | opt_PprStyle_Debug = sep [ptext (sLit "transformed branch of"), pprAStmtContext c]
1374 | otherwise = pprStmtContext c
1377 -- Used to generate the string for a *runtime* error message
1378 matchContextErrString :: Outputable id => HsMatchContext id -> SDoc
1379 matchContextErrString (FunRhs fun _) = ptext (sLit "function") <+> ppr fun
1380 matchContextErrString CaseAlt = ptext (sLit "case")
1381 matchContextErrString PatBindRhs = ptext (sLit "pattern binding")
1382 matchContextErrString RecUpd = ptext (sLit "record update")
1383 matchContextErrString LambdaExpr = ptext (sLit "lambda")
1384 matchContextErrString ProcExpr = ptext (sLit "proc")
1385 matchContextErrString ThPatQuote = panic "matchContextErrString" -- Not used at runtime
1386 matchContextErrString (StmtCtxt (ParStmtCtxt c)) = matchContextErrString (StmtCtxt c)
1387 matchContextErrString (StmtCtxt (TransStmtCtxt c)) = matchContextErrString (StmtCtxt c)
1388 matchContextErrString (StmtCtxt (PatGuard _)) = ptext (sLit "pattern guard")
1389 matchContextErrString (StmtCtxt GhciStmt) = ptext (sLit "interactive GHCi command")
1390 matchContextErrString (StmtCtxt DoExpr) = ptext (sLit "'do' block")
1391 matchContextErrString (StmtCtxt ArrowExpr) = ptext (sLit "'do' block")
1392 matchContextErrString (StmtCtxt MDoExpr) = ptext (sLit "'mdo' block")
1393 matchContextErrString (StmtCtxt ListComp) = ptext (sLit "list comprehension")
1394 matchContextErrString (StmtCtxt MonadComp) = ptext (sLit "monad comprehension")
1395 matchContextErrString (StmtCtxt PArrComp) = ptext (sLit "array comprehension")
1399 pprMatchInCtxt :: (OutputableBndr idL, OutputableBndr idR)
1400 => HsMatchContext idL -> Match idR -> SDoc
1401 pprMatchInCtxt ctxt match = hang (ptext (sLit "In") <+> pprMatchContext ctxt <> colon)
1402 4 (pprMatch ctxt match)
1404 pprStmtInCtxt :: (OutputableBndr idL, OutputableBndr idR)
1405 => HsStmtContext idL -> StmtLR idL idR -> SDoc
1406 pprStmtInCtxt ctxt (LastStmt e _)
1407 | isListCompExpr ctxt -- For [ e | .. ], do not mutter about "stmts"
1408 = hang (ptext (sLit "In the expression:")) 2 (ppr e)
1410 pprStmtInCtxt ctxt stmt
1411 = hang (ptext (sLit "In a stmt of") <+> pprAStmtContext ctxt <> colon)
1414 -- For Group and Transform Stmts, don't print the nested stmts!
1415 ppr_stmt (TransStmt { trS_by = by, trS_using = using
1416 , trS_form = form }) = pprTransStmt by using form
1417 ppr_stmt stmt = pprStmt stmt