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 -- Operator applications:
110 -- NB Bracketed ops such as (+) come out as Vars.
112 -- NB We need an expr for the operator in an OpApp/Section since
113 -- the typechecker may need to apply the operator to a few types.
115 | OpApp (LHsExpr id) -- left operand
116 (LHsExpr id) -- operator
117 Fixity -- Renamer adds fixity; bottom until then
118 (LHsExpr id) -- right operand
120 | NegApp (LHsExpr id) -- negated expr
121 (SyntaxExpr id) -- Name of 'negate'
123 | HsPar (LHsExpr id) -- parenthesised expr
125 | SectionL (LHsExpr id) -- operand
126 (LHsExpr id) -- operator
127 | SectionR (LHsExpr id) -- operator
128 (LHsExpr id) -- operand
130 | ExplicitTuple -- Used for explicit tuples and sections thereof
134 | HsCase (LHsExpr id)
137 | HsIf (Maybe (SyntaxExpr id)) -- cond function
138 -- Nothing => use the built-in 'if'
139 -- See Note [Rebindable if]
140 (LHsExpr id) -- predicate
141 (LHsExpr id) -- then part
142 (LHsExpr id) -- else part
144 | HsLet (HsLocalBinds id) -- let(rec)
147 | HsDo (HsStmtContext Name) -- The parameterisation is unimportant
148 -- because in this context we never use
149 -- the PatGuard or ParStmt variant
150 [LStmt id] -- "do":one or more stmts
151 PostTcType -- Type of the whole expression
153 | ExplicitList -- syntactic list
154 PostTcType -- Gives type of components of list
157 | ExplicitPArr -- syntactic parallel array: [:e1, ..., en:]
158 PostTcType -- type of elements of the parallel array
161 -- Record construction
162 | RecordCon (Located id) -- The constructor. After type checking
163 -- it's the dataConWrapId of the constructor
164 PostTcExpr -- Data con Id applied to type args
168 | RecordUpd (LHsExpr id)
170 -- (HsMatchGroup Id) -- Filled in by the type checker to be
171 -- -- a match that does the job
172 [DataCon] -- Filled in by the type checker to the
173 -- _non-empty_ list of DataCons that have
174 -- all the upd'd fields
175 [PostTcType] -- Argument types of *input* record type
176 [PostTcType] -- and *output* record type
177 -- For a type family, the arg types are of the *instance* tycon,
178 -- not the family tycon
180 | ExprWithTySig -- e :: type
184 | ExprWithTySigOut -- TRANSLATION
186 (LHsType Name) -- Retain the signature for
187 -- round-tripping purposes
189 | ArithSeq -- arithmetic sequence
193 | PArrSeq -- arith. sequence for parallel array
194 PostTcExpr -- [:e1..e2:] or [:e1, e2..e3:]
197 | HsSCC FastString -- "set cost centre" SCC pragma
198 (LHsExpr id) -- expr whose cost is to be measured
200 | HsCoreAnn FastString -- hdaume: core annotation
203 -----------------------------------------------------------
204 -- MetaHaskell Extensions
206 | HsBracket (HsBracket id)
208 | HsBracketOut (HsBracket Name) -- Output of the type checker is
210 [PendingSplice] -- renamed expression, plus
211 -- _typechecked_ splices to be
212 -- pasted back in by the desugarer
214 | HsSpliceE (HsSplice id)
216 | HsQuasiQuoteE (HsQuasiQuote id)
217 -- See Note [Quasi-quote overview] in TcSplice
219 -----------------------------------------------------------
220 -- Arrow notation extension
222 | HsProc (LPat id) -- arrow abstraction, proc
223 (LHsCmdTop id) -- body of the abstraction
224 -- always has an empty stack
226 ---------------------------------------
227 -- The following are commands, not expressions proper
229 | HsArrApp -- Arrow tail, or arrow application (f -< arg)
230 (LHsExpr id) -- arrow expression, f
231 (LHsExpr id) -- input expression, arg
232 PostTcType -- type of the arrow expressions f,
233 -- of the form a t t', where arg :: t
234 HsArrAppType -- higher-order (-<<) or first-order (-<)
235 Bool -- True => right-to-left (f -< arg)
236 -- False => left-to-right (arg >- f)
238 | HsArrForm -- Command formation, (| e cmd1 .. cmdn |)
239 (LHsExpr id) -- the operator
240 -- after type-checking, a type abstraction to be
241 -- applied to the type of the local environment tuple
242 (Maybe Fixity) -- fixity (filled in by the renamer), for forms that
243 -- were converted from OpApp's by the renamer
244 [LHsCmdTop id] -- argument commands
247 ---------------------------------------
248 -- Haskell program coverage (Hpc) Support
251 Int -- module-local tick number
252 [id] -- variables in scope
253 (LHsExpr id) -- sub-expression
256 Int -- module-local tick number for True
257 Int -- module-local tick number for False
258 (LHsExpr id) -- sub-expression
260 | HsTickPragma -- A pragma introduced tick
261 (FastString,(Int,Int),(Int,Int)) -- external span for this tick
264 ---------------------------------------
265 -- These constructors only appear temporarily in the parser.
266 -- The renamer translates them into the Right Thing.
268 | EWildPat -- wildcard
270 | EAsPat (Located id) -- as pattern
273 | EViewPat (LHsExpr id) -- view pattern
276 | ELazyPat (LHsExpr id) -- ~ pattern
278 | HsType (LHsType id) -- Explicit type argument; e.g f {| Int |} x y
280 ---------------------------------------
281 -- Finally, HsWrap appears only in typechecker output
283 | HsWrap HsWrapper -- TRANSLATION
285 deriving (Data, Typeable)
287 -- HsTupArg is used for tuple sections
288 -- (,a,) is represented by ExplicitTuple [Mising ty1, Present a, Missing ty3]
289 -- Which in turn stands for (\x:ty1 \y:ty2. (x,a,y))
291 = Present (LHsExpr id) -- The argument
292 | Missing PostTcType -- The argument is missing, but this is its type
293 deriving (Data, Typeable)
295 tupArgPresent :: HsTupArg id -> Bool
296 tupArgPresent (Present {}) = True
297 tupArgPresent (Missing {}) = False
299 type PendingSplice = (Name, LHsExpr Id) -- Typechecked splices, waiting to be
300 -- pasted back in by the desugarer
305 The rebindable syntax for 'if' is a bit special, because when
306 rebindable syntax is *off* we do not want to treat
308 as if it was an application (ifThenElse c t e). Why not?
309 Because we allow an 'if' to return *unboxed* results, thus
310 if blah then 3# else 4#
311 whereas that would not be possible using a all to a polymorphic function
312 (because you can't call a polymorphic function at an unboxed type).
314 So we use Nothing to mean "use the old built-in typing rule".
317 instance OutputableBndr id => Outputable (HsExpr id) where
318 ppr expr = pprExpr expr
322 -----------------------
323 -- pprExpr, pprLExpr, pprBinds call pprDeeper;
324 -- the underscore versions do not
325 pprLExpr :: OutputableBndr id => LHsExpr id -> SDoc
326 pprLExpr (L _ e) = pprExpr e
328 pprExpr :: OutputableBndr id => HsExpr id -> SDoc
329 pprExpr e | isAtomicHsExpr e || isQuietHsExpr e = ppr_expr e
330 | otherwise = pprDeeper (ppr_expr e)
332 isQuietHsExpr :: HsExpr id -> Bool
333 -- Parentheses do display something, but it gives little info and
334 -- if we go deeper when we go inside them then we get ugly things
336 isQuietHsExpr (HsPar _) = True
337 -- applications don't display anything themselves
338 isQuietHsExpr (HsApp _ _) = True
339 isQuietHsExpr (OpApp _ _ _ _) = True
340 isQuietHsExpr _ = False
342 pprBinds :: (OutputableBndr idL, OutputableBndr idR)
343 => HsLocalBindsLR idL idR -> SDoc
344 pprBinds b = pprDeeper (ppr b)
346 -----------------------
347 ppr_lexpr :: OutputableBndr id => LHsExpr id -> SDoc
348 ppr_lexpr e = ppr_expr (unLoc e)
350 ppr_expr :: OutputableBndr id => HsExpr id -> SDoc
351 ppr_expr (HsVar v) = pprHsVar v
352 ppr_expr (HsIPVar v) = ppr v
353 ppr_expr (HsLit lit) = ppr lit
354 ppr_expr (HsOverLit lit) = ppr lit
355 ppr_expr (HsPar e) = parens (ppr_lexpr e)
357 ppr_expr (HsCoreAnn s e)
358 = vcat [ptext (sLit "HsCoreAnn") <+> ftext s, ppr_lexpr e]
360 ppr_expr (HsApp e1 e2)
361 = let (fun, args) = collect_args e1 [e2] in
362 hang (ppr_lexpr fun) 2 (sep (map pprParendExpr args))
364 collect_args (L _ (HsApp fun arg)) args = collect_args fun (arg:args)
365 collect_args fun args = (fun, args)
367 ppr_expr (OpApp e1 op _ e2)
369 HsVar v -> pp_infixly v
372 pp_e1 = pprDebugParendExpr e1 -- In debug mode, add parens
373 pp_e2 = pprDebugParendExpr e2 -- to make precedence clear
376 = hang (ppr op) 2 (sep [pp_e1, pp_e2])
379 = sep [nest 2 pp_e1, pprHsInfix v, nest 2 pp_e2]
381 ppr_expr (NegApp e _) = char '-' <+> pprDebugParendExpr e
383 ppr_expr (SectionL expr op)
385 HsVar v -> pp_infixly v
388 pp_expr = pprDebugParendExpr expr
390 pp_prefixly = hang (hsep [text " \\ x_ ->", ppr op])
391 4 (hsep [pp_expr, ptext (sLit "x_ )")])
392 pp_infixly v = (sep [pp_expr, pprHsInfix v])
394 ppr_expr (SectionR op expr)
396 HsVar v -> pp_infixly v
399 pp_expr = pprDebugParendExpr expr
401 pp_prefixly = hang (hsep [text "( \\ x_ ->", ppr op, ptext (sLit "x_")])
402 4 ((<>) pp_expr rparen)
404 = (sep [pprHsInfix v, pp_expr])
406 ppr_expr (ExplicitTuple exprs boxity)
407 = tupleParens boxity (fcat (ppr_tup_args exprs))
410 ppr_tup_args (Present e : es) = (ppr_lexpr e <> punc es) : ppr_tup_args es
411 ppr_tup_args (Missing _ : es) = punc es : ppr_tup_args es
413 punc (Present {} : _) = comma <> space
414 punc (Missing {} : _) = comma
417 --avoid using PatternSignatures for stage1 code portability
418 ppr_expr exprType@(HsLam matches)
419 = pprMatches (LambdaExpr `asTypeOf` idType exprType) matches
420 where idType :: HsExpr id -> HsMatchContext id; idType = undefined
422 ppr_expr exprType@(HsCase expr matches)
423 = sep [ sep [ptext (sLit "case"), nest 4 (ppr expr), ptext (sLit "of {")],
424 nest 2 (pprMatches (CaseAlt `asTypeOf` idType exprType) matches <+> char '}') ]
425 where idType :: HsExpr id -> HsMatchContext id; idType = undefined
427 ppr_expr (HsIf _ e1 e2 e3)
428 = sep [hsep [ptext (sLit "if"), nest 2 (ppr e1), ptext (sLit "then")],
433 -- special case: let ... in let ...
434 ppr_expr (HsLet binds expr@(L _ (HsLet _ _)))
435 = sep [hang (ptext (sLit "let")) 2 (hsep [pprBinds binds, ptext (sLit "in")]),
438 ppr_expr (HsLet binds expr)
439 = sep [hang (ptext (sLit "let")) 2 (pprBinds binds),
440 hang (ptext (sLit "in")) 2 (ppr expr)]
442 ppr_expr (HsDo do_or_list_comp stmts _) = pprDo do_or_list_comp stmts
444 ppr_expr (ExplicitList _ exprs)
445 = brackets (pprDeeperList fsep (punctuate comma (map ppr_lexpr exprs)))
447 ppr_expr (ExplicitPArr _ exprs)
448 = pa_brackets (pprDeeperList fsep (punctuate comma (map ppr_lexpr exprs)))
450 ppr_expr (RecordCon con_id _ rbinds)
451 = hang (ppr con_id) 2 (ppr rbinds)
453 ppr_expr (RecordUpd aexp rbinds _ _ _)
454 = hang (pprParendExpr aexp) 2 (ppr rbinds)
456 ppr_expr (ExprWithTySig expr sig)
457 = hang (nest 2 (ppr_lexpr expr) <+> dcolon)
459 ppr_expr (ExprWithTySigOut expr sig)
460 = hang (nest 2 (ppr_lexpr expr) <+> dcolon)
463 ppr_expr (ArithSeq _ info) = brackets (ppr info)
464 ppr_expr (PArrSeq _ info) = pa_brackets (ppr info)
466 ppr_expr EWildPat = char '_'
467 ppr_expr (ELazyPat e) = char '~' <> pprParendExpr e
468 ppr_expr (EAsPat v e) = ppr v <> char '@' <> pprParendExpr e
469 ppr_expr (EViewPat p e) = ppr p <+> ptext (sLit "->") <+> ppr e
471 ppr_expr (HsSCC lbl expr)
472 = sep [ ptext (sLit "_scc_") <+> doubleQuotes (ftext lbl),
475 ppr_expr (HsWrap co_fn e) = pprHsWrapper (pprExpr e) co_fn
476 ppr_expr (HsType id) = ppr id
478 ppr_expr (HsSpliceE s) = pprSplice s
479 ppr_expr (HsBracket b) = pprHsBracket b
480 ppr_expr (HsBracketOut e []) = ppr e
481 ppr_expr (HsBracketOut e ps) = ppr e $$ ptext (sLit "pending") <+> ppr ps
482 ppr_expr (HsQuasiQuoteE qq) = ppr qq
484 ppr_expr (HsProc pat (L _ (HsCmdTop cmd _ _ _)))
485 = hsep [ptext (sLit "proc"), ppr pat, ptext (sLit "->"), ppr cmd]
487 ppr_expr (HsTick tickId vars exp)
488 = pprTicks (ppr exp) $
489 hcat [ptext (sLit "tick<"),
492 hsep (map pprHsVar vars),
495 ppr_expr (HsBinTick tickIdTrue tickIdFalse exp)
496 = pprTicks (ppr exp) $
497 hcat [ptext (sLit "bintick<"),
502 ppr exp,ptext (sLit ")")]
503 ppr_expr (HsTickPragma externalSrcLoc exp)
504 = pprTicks (ppr exp) $
505 hcat [ptext (sLit "tickpragma<"),
511 ppr_expr (HsArrApp arrow arg _ HsFirstOrderApp True)
512 = hsep [ppr_lexpr arrow, ptext (sLit "-<"), ppr_lexpr arg]
513 ppr_expr (HsArrApp arrow arg _ HsFirstOrderApp False)
514 = hsep [ppr_lexpr arg, ptext (sLit ">-"), ppr_lexpr arrow]
515 ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp True)
516 = hsep [ppr_lexpr arrow, ptext (sLit "-<<"), ppr_lexpr arg]
517 ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp False)
518 = hsep [ppr_lexpr arg, ptext (sLit ">>-"), ppr_lexpr arrow]
520 ppr_expr (HsArrForm (L _ (HsVar v)) (Just _) [arg1, arg2])
521 = sep [pprCmdArg (unLoc arg1), hsep [pprHsInfix v, pprCmdArg (unLoc arg2)]]
522 ppr_expr (HsArrForm op _ args)
523 = hang (ptext (sLit "(|") <> ppr_lexpr op)
524 4 (sep (map (pprCmdArg.unLoc) args) <> ptext (sLit "|)"))
526 pprCmdArg :: OutputableBndr id => HsCmdTop id -> SDoc
527 pprCmdArg (HsCmdTop cmd@(L _ (HsArrForm _ Nothing [])) _ _ _)
529 pprCmdArg (HsCmdTop cmd _ _ _)
530 = parens (ppr_lexpr cmd)
532 instance OutputableBndr id => Outputable (HsCmdTop id) where
535 -- add parallel array brackets around a document
537 pa_brackets :: SDoc -> SDoc
538 pa_brackets p = ptext (sLit "[:") <> p <> ptext (sLit ":]")
541 HsSyn records exactly where the user put parens, with HsPar.
542 So generally speaking we print without adding any parens.
543 However, some code is internally generated, and in some places
544 parens are absolutely required; so for these places we use
545 pprParendExpr (but don't print double parens of course).
547 For operator applications we don't add parens, because the oprerator
548 fixities should do the job, except in debug mode (-dppr-debug) so we
549 can see the structure of the parse tree.
552 pprDebugParendExpr :: OutputableBndr id => LHsExpr id -> SDoc
553 pprDebugParendExpr expr
554 = getPprStyle (\sty ->
555 if debugStyle sty then pprParendExpr expr
558 pprParendExpr :: OutputableBndr id => LHsExpr id -> SDoc
561 pp_as_was = pprLExpr expr
562 -- Using pprLExpr makes sure that we go 'deeper'
563 -- I think that is usually (always?) right
566 ArithSeq {} -> pp_as_was
567 PArrSeq {} -> pp_as_was
568 HsLit {} -> pp_as_was
569 HsOverLit {} -> pp_as_was
570 HsVar {} -> pp_as_was
571 HsIPVar {} -> pp_as_was
572 ExplicitTuple {} -> pp_as_was
573 ExplicitList {} -> pp_as_was
574 ExplicitPArr {} -> pp_as_was
575 HsPar {} -> pp_as_was
576 HsBracket {} -> pp_as_was
577 HsBracketOut _ [] -> pp_as_was
579 | isListCompExpr sc -> pp_as_was
580 _ -> parens pp_as_was
582 isAtomicHsExpr :: HsExpr id -> Bool -- A single token
583 isAtomicHsExpr (HsVar {}) = True
584 isAtomicHsExpr (HsLit {}) = True
585 isAtomicHsExpr (HsOverLit {}) = True
586 isAtomicHsExpr (HsIPVar {}) = True
587 isAtomicHsExpr (HsWrap _ e) = isAtomicHsExpr e
588 isAtomicHsExpr (HsPar e) = isAtomicHsExpr (unLoc e)
589 isAtomicHsExpr _ = False
592 %************************************************************************
594 \subsection{Commands (in arrow abstractions)}
596 %************************************************************************
598 We re-use HsExpr to represent these.
601 type HsCmd id = HsExpr id
603 type LHsCmd id = LHsExpr id
605 data HsArrAppType = HsHigherOrderApp | HsFirstOrderApp
606 deriving (Data, Typeable)
609 The legal constructors for commands are:
611 = HsArrApp ... -- as above
613 | HsArrForm ... -- as above
618 | HsLam (Match id) -- kappa
620 -- the renamer turns this one into HsArrForm
621 | OpApp (HsExpr id) -- left operand
622 (HsCmd id) -- operator
623 Fixity -- Renamer adds fixity; bottom until then
624 (HsCmd id) -- right operand
626 | HsPar (HsCmd id) -- parenthesised command
629 [Match id] -- bodies are HsCmd's
632 | HsIf (Maybe (SyntaxExpr id)) -- cond function
633 (HsExpr id) -- predicate
634 (HsCmd id) -- then part
635 (HsCmd id) -- else part
638 | HsLet (HsLocalBinds id) -- let(rec)
641 | HsDo (HsStmtContext Name) -- The parameterisation is unimportant
642 -- because in this context we never use
643 -- the PatGuard or ParStmt variant
644 [Stmt id] -- HsExpr's are really HsCmd's
645 PostTcType -- Type of the whole expression
648 Top-level command, introducing a new arrow.
649 This may occur inside a proc (where the stack is empty) or as an
650 argument of a command-forming operator.
653 type LHsCmdTop id = Located (HsCmdTop id)
656 = HsCmdTop (LHsCmd id)
657 [PostTcType] -- types of inputs on the command's stack
658 PostTcType -- return type of the command
659 (SyntaxTable id) -- after type checking:
660 -- names used in the command's desugaring
661 deriving (Data, Typeable)
664 %************************************************************************
666 \subsection{Record binds}
668 %************************************************************************
671 type HsRecordBinds id = HsRecFields id (LHsExpr id)
676 %************************************************************************
678 \subsection{@Match@, @GRHSs@, and @GRHS@ datatypes}
680 %************************************************************************
682 @Match@es are sets of pattern bindings and right hand sides for
683 functions, patterns or case branches. For example, if a function @g@
689 then \tr{g} has two @Match@es: @(x,y) = y@ and @((x:ys),y) = y+1@.
691 It is always the case that each element of an @[Match]@ list has the
692 same number of @pats@s inside it. This corresponds to saying that
693 a function defined by pattern matching must have the same number of
694 patterns in each equation.
699 [LMatch id] -- The alternatives
700 PostTcType -- The type is the type of the entire group
701 -- t1 -> ... -> tn -> tr
702 -- where there are n patterns
703 deriving (Data, Typeable)
705 type LMatch id = Located (Match id)
709 [LPat id] -- The patterns
710 (Maybe (LHsType id)) -- A type signature for the result of the match
711 -- Nothing after typechecking
713 deriving (Data, Typeable)
715 isEmptyMatchGroup :: MatchGroup id -> Bool
716 isEmptyMatchGroup (MatchGroup ms _) = null ms
718 matchGroupArity :: MatchGroup id -> Arity
719 matchGroupArity (MatchGroup [] _)
720 = panic "matchGroupArity" -- Precondition: MatchGroup is non-empty
721 matchGroupArity (MatchGroup (match:matches) _)
722 = ASSERT( all ((== n_pats) . length . hsLMatchPats) matches )
723 -- Assertion just checks that all the matches have the same number of pats
726 n_pats = length (hsLMatchPats match)
728 hsLMatchPats :: LMatch id -> [LPat id]
729 hsLMatchPats (L _ (Match pats _ _)) = pats
731 -- | GRHSs are used both for pattern bindings and for Matches
734 grhssGRHSs :: [LGRHS id], -- ^ Guarded RHSs
735 grhssLocalBinds :: (HsLocalBinds id) -- ^ The where clause
736 } deriving (Data, Typeable)
738 type LGRHS id = Located (GRHS id)
740 -- | Guarded Right Hand Side.
741 data GRHS id = GRHS [LStmt id] -- Guards
742 (LHsExpr id) -- Right hand side
743 deriving (Data, Typeable)
746 We know the list must have at least one @Match@ in it.
749 pprMatches :: (OutputableBndr idL, OutputableBndr idR) => HsMatchContext idL -> MatchGroup idR -> SDoc
750 pprMatches ctxt (MatchGroup matches _)
751 = vcat (map (pprMatch ctxt) (map unLoc matches))
752 -- Don't print the type; it's only a place-holder before typechecking
754 -- Exported to HsBinds, which can't see the defn of HsMatchContext
755 pprFunBind :: (OutputableBndr idL, OutputableBndr idR) => idL -> Bool -> MatchGroup idR -> SDoc
756 pprFunBind fun inf matches = pprMatches (FunRhs fun inf) matches
758 -- Exported to HsBinds, which can't see the defn of HsMatchContext
759 pprPatBind :: (OutputableBndr bndr, OutputableBndr id)
760 => LPat bndr -> GRHSs id -> SDoc
761 pprPatBind pat ty@(grhss)
762 = sep [ppr pat, nest 2 (pprGRHSs (PatBindRhs `asTypeOf` idType ty) grhss)]
763 --avoid using PatternSignatures for stage1 code portability
764 where idType :: GRHSs id -> HsMatchContext id; idType = undefined
767 pprMatch :: (OutputableBndr idL, OutputableBndr idR) => HsMatchContext idL -> Match idR -> SDoc
768 pprMatch ctxt (Match pats maybe_ty grhss)
769 = sep [ sep (herald : map (nest 2 . pprParendLPat) other_pats)
770 , nest 2 ppr_maybe_ty
771 , nest 2 (pprGRHSs ctxt grhss) ]
776 | not is_infix -> (ppr fun, pats)
778 -- Not pprBndr; the AbsBinds will
779 -- have printed the signature
781 | null pats2 -> (pp_infix, [])
784 | otherwise -> (parens pp_infix, pats2)
787 pp_infix = pprParendLPat pat1 <+> ppr fun <+> pprParendLPat pat2
789 LambdaExpr -> (char '\\', pats)
791 _ -> ASSERT( null pats1 )
792 (ppr pat1, []) -- No parens around the single pat
796 ppr_maybe_ty = case maybe_ty of
797 Just ty -> dcolon <+> ppr ty
801 pprGRHSs :: (OutputableBndr idL, OutputableBndr idR)
802 => HsMatchContext idL -> GRHSs idR -> SDoc
803 pprGRHSs ctxt (GRHSs grhss binds)
804 = vcat (map (pprGRHS ctxt . unLoc) grhss)
805 $$ ppUnless (isEmptyLocalBinds binds)
806 (text "where" $$ nest 4 (pprBinds binds))
808 pprGRHS :: (OutputableBndr idL, OutputableBndr idR)
809 => HsMatchContext idL -> GRHS idR -> SDoc
811 pprGRHS ctxt (GRHS [] expr)
814 pprGRHS ctxt (GRHS guards expr)
815 = sep [char '|' <+> interpp'SP guards, pp_rhs ctxt expr]
817 pp_rhs :: OutputableBndr idR => HsMatchContext idL -> LHsExpr idR -> SDoc
818 pp_rhs ctxt rhs = matchSeparator ctxt <+> pprDeeper (ppr rhs)
821 %************************************************************************
823 \subsection{Do stmts and list comprehensions}
825 %************************************************************************
828 type LStmt id = Located (StmtLR id id)
829 type LStmtLR idL idR = Located (StmtLR idL idR)
831 type Stmt id = StmtLR id id
833 -- The SyntaxExprs in here are used *only* for do-notation and monad
834 -- comprehensions, which have rebindable syntax. Otherwise they are unused.
836 = LastStmt -- Always the last Stmt in ListComp, MonadComp, PArrComp,
837 -- and (after the renamer) DoExpr, MDoExpr
838 -- Not used for GhciStmt, PatGuard, which scope over other stuff
840 (SyntaxExpr idR) -- The return operator, used only for MonadComp
841 -- For ListComp, PArrComp, we use the baked-in 'return'
842 -- For DoExpr, MDoExpr, we don't appply a 'return' at all
843 -- See Note [Monad Comprehensions]
844 | BindStmt (LPat idL)
846 (SyntaxExpr idR) -- The (>>=) operator; see Note [The type of bind]
847 (SyntaxExpr idR) -- The fail operator
848 -- The fail operator is noSyntaxExpr
849 -- if the pattern match can't fail
851 | ExprStmt (LHsExpr idR) -- See Note [ExprStmt]
852 (SyntaxExpr idR) -- The (>>) operator
853 (SyntaxExpr idR) -- The `guard` operator; used only in MonadComp
854 -- See notes [Monad Comprehensions]
855 PostTcType -- Element type of the RHS (used for arrows)
857 | LetStmt (HsLocalBindsLR idL idR)
859 -- ParStmts only occur in a list/monad comprehension
860 | ParStmt [([LStmt idL], [idR])]
861 (SyntaxExpr idR) -- Polymorphic `mzip` for monad comprehensions
862 (SyntaxExpr idR) -- The `>>=` operator
863 (SyntaxExpr idR) -- Polymorphic `return` operator
864 -- with type (forall a. a -> m a)
865 -- See notes [Monad Comprehensions]
866 -- After renaming, the ids are the binders
867 -- bound by the stmts and used after themp
870 trS_form :: TransForm,
871 trS_stmts :: [LStmt idL], -- Stmts to the *left* of the 'group'
872 -- which generates the tuples to be grouped
874 trS_bndrs :: [(idR, idR)], -- See Note [TransStmt binder map]
876 trS_using :: LHsExpr idR,
877 trS_by :: Maybe (LHsExpr idR), -- "by e" (optional)
878 -- Invariant: if trS_form = GroupBy, then grp_by = Just e
880 trS_ret :: SyntaxExpr idR, -- The monomorphic 'return' function for
881 -- the inner monad comprehensions
882 trS_bind :: SyntaxExpr idR, -- The '(>>=)' operator
883 trS_fmap :: SyntaxExpr idR -- The polymorphic 'fmap' function for desugaring
884 -- Only for 'group' forms
885 } -- See Note [Monad Comprehensions]
887 -- Recursive statement (see Note [How RecStmt works] below)
889 { recS_stmts :: [LStmtLR idL idR]
891 -- The next two fields are only valid after renaming
892 , recS_later_ids :: [idR] -- The ids are a subset of the variables bound by the
893 -- stmts that are used in stmts that follow the RecStmt
895 , recS_rec_ids :: [idR] -- Ditto, but these variables are the "recursive" ones,
896 -- that are used before they are bound in the stmts of
898 -- An Id can be in both groups
899 -- Both sets of Ids are (now) treated monomorphically
900 -- See Note [How RecStmt works] for why they are separate
903 , recS_bind_fn :: SyntaxExpr idR -- The bind function
904 , recS_ret_fn :: SyntaxExpr idR -- The return function
905 , recS_mfix_fn :: SyntaxExpr idR -- The mfix function
907 -- These fields are only valid after typechecking
908 , recS_rec_rets :: [PostTcExpr] -- These expressions correspond 1-to-1 with
909 -- recS_rec_ids, and are the
910 -- expressions that should be returned by
912 -- They may not quite be the Ids themselves,
913 -- because the Id may be *polymorphic*, but
914 -- the returned thing has to be *monomorphic*,
915 -- so they may be type applications
917 , recS_ret_ty :: PostTcType -- The type of of do { stmts; return (a,b,c) }
918 -- With rebindable syntax the type might not
919 -- be quite as simple as (m (tya, tyb, tyc)).
921 deriving (Data, Typeable)
923 data TransForm -- The 'f' below is the 'using' function, 'e' is the by function
924 = ThenForm -- then f or then f by e
925 | GroupFormU -- group using f or group using f by e
926 | GroupFormB -- group by e
927 -- In the GroupByFormB, trS_using is filled in with
928 -- 'groupWith' (list comprehensions) or
929 -- 'groupM' (monad comprehensions)
930 deriving (Data, Typeable)
933 Note [The type of bind in Stmts]
934 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
935 Some Stmts, notably BindStmt, keep the (>>=) bind operator.
936 We do NOT assume that it has type
937 (>>=) :: m a -> (a -> m b) -> m b
938 In some cases (see Trac #303, #1537) it might have a more
940 (>>=) :: m i j a -> (a -> m j k b) -> m i k b
941 So we must be careful not to make assumptions about the type.
942 In particular, the monad may not be uniform throughout.
944 Note [TransStmt binder map]
945 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
946 The [(idR,idR)] in a TransStmt behaves as follows:
948 * Before renaming: []
951 [ (x27,x27), ..., (z35,z35) ]
952 These are the variables
953 bound by the stmts to the left of the 'group'
954 and used either in the 'by' clause,
955 or in the stmts following the 'group'
956 Each item is a pair of identical variables.
958 * After typechecking:
959 [ (x27:Int, x27:[Int]), ..., (z35:Bool, z35:[Bool]) ]
960 Each pair has the same unique, but different *types*.
964 ExprStmts are a bit tricky, because what they mean
965 depends on the context. Consider the following contexts:
967 A do expression of type (m res_ty)
968 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
969 * ExprStmt E any_ty: do { ....; E; ... }
971 Translation: E >> ...
973 A list comprehensions of type [elt_ty]
974 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
975 * ExprStmt E Bool: [ .. | .... E ]
977 [ .. | .... | ..., E | ... ]
979 Translation: if E then fail else ...
981 A guard list, guarding a RHS of type rhs_ty
982 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
983 * ExprStmt E Bool: f x | ..., E, ... = ...rhs...
985 Translation: if E then fail else ...
987 A monad comprehension of type (m res_ty)
988 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
989 * ExprStmt E Bool: [ .. | .... E ]
991 Translation: guard E >> ...
993 Array comprehensions are handled like list comprehensions.
995 Note [How RecStmt works]
996 ~~~~~~~~~~~~~~~~~~~~~~~~
1000 , RecStmt { recS_rec_ids = [a, c]
1001 , recS_stmts = [ BindStmt b (return (a,c))
1002 , LetStmt a = ...b...
1004 , recS_later_ids = [a, b]
1008 Here, the RecStmt binds a,b,c; but
1009 - Only a,b are used in the stmts *following* the RecStmt,
1010 - Only a,c are used in the stmts *inside* the RecStmt
1011 *before* their bindings
1013 Why do we need *both* rec_ids and later_ids? For monads they could be
1014 combined into a single set of variables, but not for arrows. That
1015 follows from the types of the respective feedback operators:
1017 mfix :: MonadFix m => (a -> m a) -> m a
1018 loop :: ArrowLoop a => a (b,d) (c,d) -> a b c
1020 * For mfix, the 'a' covers the union of the later_ids and the rec_ids
1021 * For 'loop', 'c' is the later_ids and 'd' is the rec_ids
1023 Note [Typing a RecStmt]
1024 ~~~~~~~~~~~~~~~~~~~~~~~
1025 A (RecStmt stmts) types as if you had written
1027 (v1,..,vn, _, ..., _) <- mfix (\~(_, ..., _, r1, ..., rm) ->
1029 ; return (v1,..vn, r1, ..., rm) })
1031 where v1..vn are the later_ids
1032 r1..rm are the rec_ids
1034 Note [Monad Comprehensions]
1035 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
1036 Monad comprehensions require separate functions like 'return' and
1037 '>>=' for desugaring. These functions are stored in the statements
1038 used in monad comprehensions. For example, the 'return' of the 'LastStmt'
1039 expression is used to lift the body of the monad comprehension:
1043 stmts >>= \bndrs -> return body
1045 In transform and grouping statements ('then ..' and 'then group ..') the
1046 'return' function is required for nested monad comprehensions, for example:
1048 [ body | stmts, then f, rest ]
1050 f [ env | stmts ] >>= \bndrs -> [ body | rest ]
1052 ExprStmts require the 'Control.Monad.guard' function for boolean
1055 [ body | exp, stmts ]
1057 guard exp >> [ body | stmts ]
1059 Grouping/parallel statements require the 'Control.Monad.Group.groupM' and
1060 'Control.Monad.Zip.mzip' functions:
1062 [ body | stmts, then group by e, rest]
1064 groupM [ body | stmts ] >>= \bndrs -> [ body | rest ]
1066 [ body | stmts1 | stmts2 | .. ]
1068 mzip stmts1 (mzip stmts2 (..)) >>= \(bndrs1, (bndrs2, ..)) -> return body
1070 In any other context than 'MonadComp', the fields for most of these
1071 'SyntaxExpr's stay bottom.
1075 instance (OutputableBndr idL, OutputableBndr idR) => Outputable (StmtLR idL idR) where
1076 ppr stmt = pprStmt stmt
1078 pprStmt :: (OutputableBndr idL, OutputableBndr idR) => (StmtLR idL idR) -> SDoc
1079 pprStmt (LastStmt expr _) = ifPprDebug (ptext (sLit "[last]")) <+> ppr expr
1080 pprStmt (BindStmt pat expr _ _) = hsep [ppr pat, ptext (sLit "<-"), ppr expr]
1081 pprStmt (LetStmt binds) = hsep [ptext (sLit "let"), pprBinds binds]
1082 pprStmt (ExprStmt expr _ _ _) = ppr expr
1083 pprStmt (ParStmt stmtss _ _ _) = hsep (map doStmts stmtss)
1084 where doStmts stmts = ptext (sLit "| ") <> ppr stmts
1086 pprStmt (TransStmt { trS_stmts = stmts, trS_by = by, trS_using = using, trS_form = form })
1087 = sep (ppr_lc_stmts stmts ++ [pprTransStmt by using form])
1089 pprStmt (RecStmt { recS_stmts = segment, recS_rec_ids = rec_ids
1090 , recS_later_ids = later_ids })
1091 = ptext (sLit "rec") <+>
1092 vcat [ braces (vcat (map ppr segment))
1093 , ifPprDebug (vcat [ ptext (sLit "rec_ids=") <> ppr rec_ids
1094 , ptext (sLit "later_ids=") <> ppr later_ids])]
1096 pprTransformStmt :: OutputableBndr id => [id] -> LHsExpr id -> Maybe (LHsExpr id) -> SDoc
1097 pprTransformStmt bndrs using by
1098 = sep [ ptext (sLit "then") <+> ifPprDebug (braces (ppr bndrs))
1099 , nest 2 (ppr using)
1100 , nest 2 (pprBy by)]
1102 pprTransStmt :: OutputableBndr id => Maybe (LHsExpr id)
1103 -> LHsExpr id -> TransForm
1105 pprTransStmt by using ThenForm
1106 = sep [ ptext (sLit "then"), nest 2 (ppr using), nest 2 (pprBy by)]
1107 pprTransStmt by _ GroupFormB
1108 = sep [ ptext (sLit "then group"), nest 2 (pprBy by) ]
1109 pprTransStmt by using GroupFormU
1110 = sep [ ptext (sLit "then group"), nest 2 (pprBy by), nest 2 (ptext (sLit "using") <+> ppr using)]
1112 pprBy :: OutputableBndr id => Maybe (LHsExpr id) -> SDoc
1113 pprBy Nothing = empty
1114 pprBy (Just e) = ptext (sLit "by") <+> ppr e
1116 pprDo :: OutputableBndr id => HsStmtContext any -> [LStmt id] -> SDoc
1117 pprDo DoExpr stmts = ptext (sLit "do") <+> ppr_do_stmts stmts
1118 pprDo GhciStmt stmts = ptext (sLit "do") <+> ppr_do_stmts stmts
1119 pprDo ArrowExpr stmts = ptext (sLit "do") <+> ppr_do_stmts stmts
1120 pprDo MDoExpr stmts = ptext (sLit "mdo") <+> ppr_do_stmts stmts
1121 pprDo ListComp stmts = brackets $ pprComp stmts
1122 pprDo PArrComp stmts = pa_brackets $ pprComp stmts
1123 pprDo MonadComp stmts = brackets $ pprComp stmts
1124 pprDo _ _ = panic "pprDo" -- PatGuard, ParStmtCxt
1126 ppr_do_stmts :: OutputableBndr id => [LStmt id] -> SDoc
1127 -- Print a bunch of do stmts, with explicit braces and semicolons,
1128 -- so that we are not vulnerable to layout bugs
1130 = lbrace <+> pprDeeperList vcat (punctuate semi (map ppr stmts))
1133 ppr_lc_stmts :: OutputableBndr id => [LStmt id] -> [SDoc]
1134 ppr_lc_stmts stmts = [ppr s <> comma | s <- stmts]
1136 pprComp :: OutputableBndr id => [LStmt id] -> SDoc
1137 pprComp quals -- Prints: body | qual1, ..., qualn
1139 , L _ (LastStmt body _) <- last quals
1140 = hang (ppr body <+> char '|') 2 (interpp'SP (dropTail 1 quals))
1142 = pprPanic "pprComp" (interpp'SP quals)
1145 %************************************************************************
1147 Template Haskell quotation brackets
1149 %************************************************************************
1152 data HsSplice id = HsSplice -- $z or $(f 4)
1153 id -- The id is just a unique name to
1154 (LHsExpr id) -- identify this splice point
1155 deriving (Data, Typeable)
1157 instance OutputableBndr id => Outputable (HsSplice id) where
1160 pprSplice :: OutputableBndr id => HsSplice id -> SDoc
1161 pprSplice (HsSplice n e)
1162 = char '$' <> ifPprDebug (brackets (ppr n)) <> eDoc
1164 -- We use pprLExpr to match pprParendExpr:
1165 -- Using pprLExpr makes sure that we go 'deeper'
1166 -- I think that is usually (always?) right
1167 pp_as_was = pprLExpr e
1168 eDoc = case unLoc e of
1169 HsPar _ -> pp_as_was
1170 HsVar _ -> pp_as_was
1171 _ -> parens pp_as_was
1173 data HsBracket id = ExpBr (LHsExpr id) -- [| expr |]
1174 | PatBr (LPat id) -- [p| pat |]
1175 | DecBrL [LHsDecl id] -- [d| decls |]; result of parser
1176 | DecBrG (HsGroup id) -- [d| decls |]; result of renamer
1177 | TypBr (LHsType id) -- [t| type |]
1178 | VarBr id -- 'x, ''T
1179 deriving (Data, Typeable)
1181 instance OutputableBndr id => Outputable (HsBracket id) where
1185 pprHsBracket :: OutputableBndr id => HsBracket id -> SDoc
1186 pprHsBracket (ExpBr e) = thBrackets empty (ppr e)
1187 pprHsBracket (PatBr p) = thBrackets (char 'p') (ppr p)
1188 pprHsBracket (DecBrG gp) = thBrackets (char 'd') (ppr gp)
1189 pprHsBracket (DecBrL ds) = thBrackets (char 'd') (vcat (map ppr ds))
1190 pprHsBracket (TypBr t) = thBrackets (char 't') (ppr t)
1191 pprHsBracket (VarBr n) = char '\'' <> ppr n
1192 -- Infelicity: can't show ' vs '', because
1193 -- we can't ask n what its OccName is, because the
1194 -- pretty-printer for HsExpr doesn't ask for NamedThings
1195 -- But the pretty-printer for names will show the OccName class
1197 thBrackets :: SDoc -> SDoc -> SDoc
1198 thBrackets pp_kind pp_body = char '[' <> pp_kind <> char '|' <+>
1199 pp_body <+> ptext (sLit "|]")
1202 %************************************************************************
1204 \subsection{Enumerations and list comprehensions}
1206 %************************************************************************
1209 data ArithSeqInfo id
1211 | FromThen (LHsExpr id)
1213 | FromTo (LHsExpr id)
1215 | FromThenTo (LHsExpr id)
1218 deriving (Data, Typeable)
1222 instance OutputableBndr id => Outputable (ArithSeqInfo id) where
1223 ppr (From e1) = hcat [ppr e1, pp_dotdot]
1224 ppr (FromThen e1 e2) = hcat [ppr e1, comma, space, ppr e2, pp_dotdot]
1225 ppr (FromTo e1 e3) = hcat [ppr e1, pp_dotdot, ppr e3]
1226 ppr (FromThenTo e1 e2 e3)
1227 = hcat [ppr e1, comma, space, ppr e2, pp_dotdot, ppr e3]
1230 pp_dotdot = ptext (sLit " .. ")
1234 %************************************************************************
1236 \subsection{HsMatchCtxt}
1238 %************************************************************************
1241 data HsMatchContext id -- Context of a Match
1242 = FunRhs id Bool -- Function binding for f; True <=> written infix
1243 | LambdaExpr -- Patterns of a lambda
1244 | CaseAlt -- Patterns and guards on a case alternative
1245 | ProcExpr -- Patterns of a proc
1246 | PatBindRhs -- A pattern binding eg [y] <- e = e
1248 | RecUpd -- Record update [used only in DsExpr to
1249 -- tell matchWrapper what sort of
1250 -- runtime error message to generate]
1252 | StmtCtxt (HsStmtContext id) -- Pattern of a do-stmt, list comprehension,
1253 -- pattern guard, etc
1255 | ThPatQuote -- A Template Haskell pattern quotation [p| (a,b) |]
1256 deriving (Data, Typeable)
1258 data HsStmtContext id
1261 | PArrComp -- Parallel array comprehension
1263 | DoExpr -- do { ... }
1264 | MDoExpr -- mdo { ... } ie recursive do-expression
1265 | ArrowExpr -- do-notation in an arrow-command context
1267 | GhciStmt -- A command-line Stmt in GHCi pat <- rhs
1268 | PatGuard (HsMatchContext id) -- Pattern guard for specified thing
1269 | ParStmtCtxt (HsStmtContext id) -- A branch of a parallel stmt
1270 | TransStmtCtxt (HsStmtContext id) -- A branch of a transform stmt
1271 deriving (Data, Typeable)
1275 isListCompExpr :: HsStmtContext id -> Bool
1276 -- Uses syntax [ e | quals ]
1277 isListCompExpr ListComp = True
1278 isListCompExpr PArrComp = True
1279 isListCompExpr MonadComp = True
1280 isListCompExpr _ = False
1282 isMonadCompExpr :: HsStmtContext id -> Bool
1283 isMonadCompExpr MonadComp = True
1284 isMonadCompExpr (ParStmtCtxt ctxt) = isMonadCompExpr ctxt
1285 isMonadCompExpr (TransStmtCtxt ctxt) = isMonadCompExpr ctxt
1286 isMonadCompExpr _ = False
1290 matchSeparator :: HsMatchContext id -> SDoc
1291 matchSeparator (FunRhs {}) = ptext (sLit "=")
1292 matchSeparator CaseAlt = ptext (sLit "->")
1293 matchSeparator LambdaExpr = ptext (sLit "->")
1294 matchSeparator ProcExpr = ptext (sLit "->")
1295 matchSeparator PatBindRhs = ptext (sLit "=")
1296 matchSeparator (StmtCtxt _) = ptext (sLit "<-")
1297 matchSeparator RecUpd = panic "unused"
1298 matchSeparator ThPatQuote = panic "unused"
1302 pprMatchContext :: Outputable id => HsMatchContext id -> SDoc
1303 pprMatchContext ctxt
1304 | want_an ctxt = ptext (sLit "an") <+> pprMatchContextNoun ctxt
1305 | otherwise = ptext (sLit "a") <+> pprMatchContextNoun ctxt
1307 want_an (FunRhs {}) = True -- Use "an" in front
1308 want_an ProcExpr = True
1311 pprMatchContextNoun :: Outputable id => HsMatchContext id -> SDoc
1312 pprMatchContextNoun (FunRhs fun _) = ptext (sLit "equation for")
1313 <+> quotes (ppr fun)
1314 pprMatchContextNoun CaseAlt = ptext (sLit "case alternative")
1315 pprMatchContextNoun RecUpd = ptext (sLit "record-update construct")
1316 pprMatchContextNoun ThPatQuote = ptext (sLit "Template Haskell pattern quotation")
1317 pprMatchContextNoun PatBindRhs = ptext (sLit "pattern binding")
1318 pprMatchContextNoun LambdaExpr = ptext (sLit "lambda abstraction")
1319 pprMatchContextNoun ProcExpr = ptext (sLit "arrow abstraction")
1320 pprMatchContextNoun (StmtCtxt ctxt) = ptext (sLit "pattern binding in")
1321 $$ pprStmtContext ctxt
1324 pprAStmtContext, pprStmtContext :: Outputable id => HsStmtContext id -> SDoc
1325 pprAStmtContext ctxt = article <+> pprStmtContext ctxt
1327 pp_an = ptext (sLit "an")
1328 pp_a = ptext (sLit "a")
1329 article = case ctxt of
1337 pprStmtContext GhciStmt = ptext (sLit "interactive GHCi command")
1338 pprStmtContext DoExpr = ptext (sLit "'do' block")
1339 pprStmtContext MDoExpr = ptext (sLit "'mdo' block")
1340 pprStmtContext ArrowExpr = ptext (sLit "'do' block in an arrow command")
1341 pprStmtContext ListComp = ptext (sLit "list comprehension")
1342 pprStmtContext MonadComp = ptext (sLit "monad comprehension")
1343 pprStmtContext PArrComp = ptext (sLit "array comprehension")
1344 pprStmtContext (PatGuard ctxt) = ptext (sLit "pattern guard for") $$ pprMatchContext ctxt
1346 -- Drop the inner contexts when reporting errors, else we get
1347 -- Unexpected transform statement
1348 -- in a transformed branch of
1349 -- transformed branch of
1350 -- transformed branch of monad comprehension
1351 pprStmtContext (ParStmtCtxt c)
1352 | opt_PprStyle_Debug = sep [ptext (sLit "parallel branch of"), pprAStmtContext c]
1353 | otherwise = pprStmtContext c
1354 pprStmtContext (TransStmtCtxt c)
1355 | opt_PprStyle_Debug = sep [ptext (sLit "transformed branch of"), pprAStmtContext c]
1356 | otherwise = pprStmtContext c
1359 -- Used to generate the string for a *runtime* error message
1360 matchContextErrString :: Outputable id => HsMatchContext id -> SDoc
1361 matchContextErrString (FunRhs fun _) = ptext (sLit "function") <+> ppr fun
1362 matchContextErrString CaseAlt = ptext (sLit "case")
1363 matchContextErrString PatBindRhs = ptext (sLit "pattern binding")
1364 matchContextErrString RecUpd = ptext (sLit "record update")
1365 matchContextErrString LambdaExpr = ptext (sLit "lambda")
1366 matchContextErrString ProcExpr = ptext (sLit "proc")
1367 matchContextErrString ThPatQuote = panic "matchContextErrString" -- Not used at runtime
1368 matchContextErrString (StmtCtxt (ParStmtCtxt c)) = matchContextErrString (StmtCtxt c)
1369 matchContextErrString (StmtCtxt (TransStmtCtxt c)) = matchContextErrString (StmtCtxt c)
1370 matchContextErrString (StmtCtxt (PatGuard _)) = ptext (sLit "pattern guard")
1371 matchContextErrString (StmtCtxt GhciStmt) = ptext (sLit "interactive GHCi command")
1372 matchContextErrString (StmtCtxt DoExpr) = ptext (sLit "'do' block")
1373 matchContextErrString (StmtCtxt ArrowExpr) = ptext (sLit "'do' block")
1374 matchContextErrString (StmtCtxt MDoExpr) = ptext (sLit "'mdo' block")
1375 matchContextErrString (StmtCtxt ListComp) = ptext (sLit "list comprehension")
1376 matchContextErrString (StmtCtxt MonadComp) = ptext (sLit "monad comprehension")
1377 matchContextErrString (StmtCtxt PArrComp) = ptext (sLit "array comprehension")
1381 pprMatchInCtxt :: (OutputableBndr idL, OutputableBndr idR)
1382 => HsMatchContext idL -> Match idR -> SDoc
1383 pprMatchInCtxt ctxt match = hang (ptext (sLit "In") <+> pprMatchContext ctxt <> colon)
1384 4 (pprMatch ctxt match)
1386 pprStmtInCtxt :: (OutputableBndr idL, OutputableBndr idR)
1387 => HsStmtContext idL -> StmtLR idL idR -> SDoc
1388 pprStmtInCtxt ctxt (LastStmt e _)
1389 | isListCompExpr ctxt -- For [ e | .. ], do not mutter about "stmts"
1390 = hang (ptext (sLit "In the expression:")) 2 (ppr e)
1392 pprStmtInCtxt ctxt stmt
1393 = hang (ptext (sLit "In a stmt of") <+> pprAStmtContext ctxt <> colon)
1396 -- For Group and Transform Stmts, don't print the nested stmts!
1397 ppr_stmt (TransStmt { trS_by = by, trS_using = using
1398 , trS_form = form }) = pprTransStmt by using form
1399 ppr_stmt stmt = pprStmt stmt