2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 HsExpr: Abstract Haskell syntax: expressions
11 #include "HsVersions.h"
32 %************************************************************************
34 \subsection{Expressions proper}
36 %************************************************************************
39 type LHsExpr id = Located (HsExpr id)
41 -------------------------
42 -- PostTcExpr is an evidence expression attached to the
43 -- syntax tree by the type checker (c.f. postTcType)
44 -- We use a PostTcTable where there are a bunch of pieces of
45 -- evidence, more than is convenient to keep individually
46 type PostTcExpr = HsExpr Id
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.
58 -- E.g. (>>=) is filled in before the renamer by the appropriate Name
59 -- for (>>=), and then instantiated by the type checker with its
62 type SyntaxExpr id = HsExpr id
64 noSyntaxExpr :: SyntaxExpr id -- Before renaming, and sometimes after,
65 -- (if the syntax slot makes no sense)
66 noSyntaxExpr = HsLit (HsString FSLIT("noSyntaxExpr"))
69 type SyntaxTable id = [(Name, SyntaxExpr id)]
70 -- *** Currently used only for CmdTop (sigh) ***
71 -- * Before the renamer, this list is noSyntaxTable
73 -- * After the renamer, it takes the form [(std_name, HsVar actual_name)]
74 -- For example, for the 'return' op of a monad
75 -- normal case: (GHC.Base.return, HsVar GHC.Base.return)
76 -- with rebindable syntax: (GHC.Base.return, return_22)
77 -- where return_22 is whatever "return" is in scope
79 -- * After the type checker, it takes the form [(std_name, <expression>)]
80 -- where <expression> is the evidence for the method
82 noSyntaxTable :: SyntaxTable id
86 -------------------------
88 = HsVar id -- variable
89 | HsIPVar (IPName id) -- implicit parameter
90 | HsOverLit (HsOverLit id) -- Overloaded literals
92 | HsLit HsLit -- Simple (non-overloaded) literals
94 | HsLam (MatchGroup id) -- Currently always a single match
96 | HsApp (LHsExpr id) (LHsExpr id) -- Application
98 -- Operator applications:
99 -- NB Bracketed ops such as (+) come out as Vars.
101 -- NB We need an expr for the operator in an OpApp/Section since
102 -- the typechecker may need to apply the operator to a few types.
104 | OpApp (LHsExpr id) -- left operand
105 (LHsExpr id) -- operator
106 Fixity -- Renamer adds fixity; bottom until then
107 (LHsExpr id) -- right operand
109 | NegApp (LHsExpr id) -- negated expr
110 (SyntaxExpr id) -- Name of 'negate'
112 | HsPar (LHsExpr id) -- parenthesised expr
114 | SectionL (LHsExpr id) -- operand
115 (LHsExpr id) -- operator
116 | SectionR (LHsExpr id) -- operator
117 (LHsExpr id) -- operand
119 | HsCase (LHsExpr id)
122 | HsIf (LHsExpr id) -- predicate
123 (LHsExpr id) -- then part
124 (LHsExpr id) -- else part
126 | HsLet (HsLocalBinds id) -- let(rec)
129 | HsDo (HsStmtContext Name) -- The parameterisation is unimportant
130 -- because in this context we never use
131 -- the PatGuard or ParStmt variant
132 [LStmt id] -- "do":one or more stmts
133 (LHsExpr id) -- The body; the last expression in the
134 -- 'do' of [ body | ... ] in a list comp
135 PostTcType -- Type of the whole expression
137 | ExplicitList -- syntactic list
138 PostTcType -- Gives type of components of list
141 | ExplicitPArr -- syntactic parallel array: [:e1, ..., en:]
142 PostTcType -- type of elements of the parallel array
145 | ExplicitTuple -- tuple
147 -- NB: Unit is ExplicitTuple []
148 -- for tuples, we can get the types
149 -- direct from the components
153 -- Record construction
154 | RecordCon (Located id) -- The constructor. After type checking
155 -- it's the dataConWrapId of the constructor
156 PostTcExpr -- Data con Id applied to type args
160 | RecordUpd (LHsExpr id)
162 [DataCon] -- Filled in by the type checker to the
163 -- *non-empty* list of DataCons that have
164 -- all the upd'd fields
165 [PostTcType] -- Argument types of *input* record type
166 [PostTcType] -- and *output* record type
167 -- For a type family, the arg types are of the *instance* tycon,
168 -- not the family tycon
170 | ExprWithTySig -- e :: type
174 | ExprWithTySigOut -- TRANSLATION
176 (LHsType Name) -- Retain the signature for
177 -- round-tripping purposes
179 | ArithSeq -- arithmetic sequence
183 | PArrSeq -- arith. sequence for parallel array
184 PostTcExpr -- [:e1..e2:] or [:e1, e2..e3:]
187 | HsSCC FastString -- "set cost centre" SCC pragma
188 (LHsExpr id) -- expr whose cost is to be measured
190 | HsCoreAnn FastString -- hdaume: core annotation
193 -----------------------------------------------------------
194 -- MetaHaskell Extensions
196 | HsBracket (HsBracket id)
198 | HsBracketOut (HsBracket Name) -- Output of the type checker is
200 [PendingSplice] -- renamed expression, plus
201 -- *typechecked* splices to be
202 -- pasted back in by the desugarer
204 | HsSpliceE (HsSplice id)
206 -----------------------------------------------------------
207 -- Arrow notation extension
209 | HsProc (LPat id) -- arrow abstraction, proc
210 (LHsCmdTop id) -- body of the abstraction
211 -- always has an empty stack
213 ---------------------------------------
214 -- The following are commands, not expressions proper
216 | HsArrApp -- Arrow tail, or arrow application (f -< arg)
217 (LHsExpr id) -- arrow expression, f
218 (LHsExpr id) -- input expression, arg
219 PostTcType -- type of the arrow expressions f,
220 -- of the form a t t', where arg :: t
221 HsArrAppType -- higher-order (-<<) or first-order (-<)
222 Bool -- True => right-to-left (f -< arg)
223 -- False => left-to-right (arg >- f)
225 | HsArrForm -- Command formation, (| e cmd1 .. cmdn |)
226 (LHsExpr id) -- the operator
227 -- after type-checking, a type abstraction to be
228 -- applied to the type of the local environment tuple
229 (Maybe Fixity) -- fixity (filled in by the renamer), for forms that
230 -- were converted from OpApp's by the renamer
231 [LHsCmdTop id] -- argument commands
234 ---------------------------------------
235 -- Haskell program coverage (Hpc) Support
238 Int -- module-local tick number
239 [id] -- variables in scope
240 (LHsExpr id) -- sub-expression
243 Int -- module-local tick number for True
244 Int -- module-local tick number for False
245 (LHsExpr id) -- sub-expression
247 | HsTickPragma -- A pragma introduced tick
248 (FastString,(Int,Int),(Int,Int)) -- external span for this tick
251 ---------------------------------------
252 -- These constructors only appear temporarily in the parser.
253 -- The renamer translates them into the Right Thing.
255 | EWildPat -- wildcard
257 | EAsPat (Located id) -- as pattern
260 | EViewPat (LHsExpr id) -- view pattern
263 | ELazyPat (LHsExpr id) -- ~ pattern
265 | HsType (LHsType id) -- Explicit type argument; e.g f {| Int |} x y
267 ---------------------------------------
268 -- Finally, HsWrap appears only in typechecker output
270 | HsWrap HsWrapper -- TRANSLATION
273 type PendingSplice = (Name, LHsExpr Id) -- Typechecked splices, waiting to be
274 -- pasted back in by the desugarer
277 A @Dictionary@, unless of length 0 or 1, becomes a tuple. A
278 @ClassDictLam dictvars methods expr@ is, therefore:
280 \ x -> case x of ( dictvars-and-methods-tuple ) -> expr
284 instance OutputableBndr id => Outputable (HsExpr id) where
285 ppr expr = pprExpr expr
289 -----------------------
290 -- pprExpr, pprLExpr, pprBinds call pprDeeper;
291 -- the underscore versions do not
292 pprLExpr :: OutputableBndr id => LHsExpr id -> SDoc
293 pprLExpr (L _ e) = pprExpr e
295 pprExpr :: OutputableBndr id => HsExpr id -> SDoc
296 pprExpr e | isAtomicHsExpr e || isQuietHsExpr e = ppr_expr e
297 | otherwise = pprDeeper (ppr_expr e)
299 isQuietHsExpr :: HsExpr id -> Bool
300 -- Parentheses do display something, but it gives little info and
301 -- if we go deeper when we go inside them then we get ugly things
303 isQuietHsExpr (HsPar _) = True
304 -- applications don't display anything themselves
305 isQuietHsExpr (HsApp _ _) = True
306 isQuietHsExpr (OpApp _ _ _ _) = True
307 isQuietHsExpr _ = False
309 pprBinds :: (OutputableBndr idL, OutputableBndr idR)
310 => HsLocalBindsLR idL idR -> SDoc
311 pprBinds b = pprDeeper (ppr b)
313 -----------------------
314 ppr_lexpr :: OutputableBndr id => LHsExpr id -> SDoc
315 ppr_lexpr e = ppr_expr (unLoc e)
317 ppr_expr :: OutputableBndr id => HsExpr id -> SDoc
318 ppr_expr (HsVar v) = pprHsVar v
319 ppr_expr (HsIPVar v) = ppr v
320 ppr_expr (HsLit lit) = ppr lit
321 ppr_expr (HsOverLit lit) = ppr lit
322 ppr_expr (HsPar e) = parens (ppr_lexpr e)
324 ppr_expr (HsCoreAnn s e)
325 = vcat [ptext SLIT("HsCoreAnn") <+> ftext s, ppr_lexpr e]
327 ppr_expr (HsApp e1 e2)
328 = let (fun, args) = collect_args e1 [e2] in
329 hang (ppr_lexpr fun) 2 (sep (map pprParendExpr args))
331 collect_args (L _ (HsApp fun arg)) args = collect_args fun (arg:args)
332 collect_args fun args = (fun, args)
334 ppr_expr (OpApp e1 op _ e2)
336 HsVar v -> pp_infixly v
339 pp_e1 = pprDebugParendExpr e1 -- In debug mode, add parens
340 pp_e2 = pprDebugParendExpr e2 -- to make precedence clear
343 = hang (ppr op) 2 (sep [pp_e1, pp_e2])
346 = sep [nest 2 pp_e1, pprInfix v, nest 2 pp_e2]
348 ppr_expr (NegApp e _) = char '-' <+> pprDebugParendExpr e
350 ppr_expr (SectionL expr op)
352 HsVar v -> pp_infixly v
355 pp_expr = pprDebugParendExpr expr
357 pp_prefixly = hang (hsep [text " \\ x_ ->", ppr op])
358 4 (hsep [pp_expr, ptext SLIT("x_ )")])
359 pp_infixly v = (sep [pp_expr, pprInfix v])
361 ppr_expr (SectionR op expr)
363 HsVar v -> pp_infixly v
366 pp_expr = pprDebugParendExpr expr
368 pp_prefixly = hang (hsep [text "( \\ x_ ->", ppr op, ptext SLIT("x_")])
369 4 ((<>) pp_expr rparen)
371 = (sep [pprInfix v, pp_expr])
373 --avoid using PatternSignatures for stage1 code portability
374 ppr_expr exprType@(HsLam matches)
375 = pprMatches (LambdaExpr `asTypeOf` idType exprType) matches
376 where idType :: HsExpr id -> HsMatchContext id; idType = undefined
378 ppr_expr exprType@(HsCase expr matches)
379 = sep [ sep [ptext SLIT("case"), nest 4 (ppr expr), ptext SLIT("of")],
380 nest 2 (pprMatches (CaseAlt `asTypeOf` idType exprType) matches) ]
381 where idType :: HsExpr id -> HsMatchContext id; idType = undefined
383 ppr_expr (HsIf e1 e2 e3)
384 = sep [hsep [ptext SLIT("if"), nest 2 (ppr e1), ptext SLIT("then")],
389 -- special case: let ... in let ...
390 ppr_expr (HsLet binds expr@(L _ (HsLet _ _)))
391 = sep [hang (ptext SLIT("let")) 2 (hsep [pprBinds binds, ptext SLIT("in")]),
394 ppr_expr (HsLet binds expr)
395 = sep [hang (ptext SLIT("let")) 2 (pprBinds binds),
396 hang (ptext SLIT("in")) 2 (ppr expr)]
398 ppr_expr (HsDo do_or_list_comp stmts body _) = pprDo do_or_list_comp stmts body
400 ppr_expr (ExplicitList _ exprs)
401 = brackets (pprDeeperList fsep (punctuate comma (map ppr_lexpr exprs)))
403 ppr_expr (ExplicitPArr _ exprs)
404 = pa_brackets (pprDeeperList fsep (punctuate comma (map ppr_lexpr exprs)))
406 ppr_expr (ExplicitTuple exprs boxity)
407 = tupleParens boxity (sep (punctuate comma (map ppr_lexpr exprs)))
409 ppr_expr (RecordCon con_id _ rbinds)
410 = hang (ppr con_id) 2 (ppr rbinds)
412 ppr_expr (RecordUpd aexp rbinds _ _ _)
413 = hang (pprParendExpr aexp) 2 (ppr rbinds)
415 ppr_expr (ExprWithTySig expr sig)
416 = hang (nest 2 (ppr_lexpr expr) <+> dcolon)
418 ppr_expr (ExprWithTySigOut expr sig)
419 = hang (nest 2 (ppr_lexpr expr) <+> dcolon)
422 ppr_expr (ArithSeq _ info) = brackets (ppr info)
423 ppr_expr (PArrSeq _ info) = pa_brackets (ppr info)
425 ppr_expr EWildPat = char '_'
426 ppr_expr (ELazyPat e) = char '~' <> pprParendExpr e
427 ppr_expr (EAsPat v e) = ppr v <> char '@' <> pprParendExpr e
428 ppr_expr (EViewPat p e) = ppr p <+> ptext SLIT("->") <+> ppr e
430 ppr_expr (HsSCC lbl expr)
431 = sep [ ptext SLIT("_scc_") <+> doubleQuotes (ftext lbl),
434 ppr_expr (HsWrap co_fn e) = pprHsWrapper (pprExpr e) co_fn
435 ppr_expr (HsType id) = ppr id
437 ppr_expr (HsSpliceE s) = pprSplice s
438 ppr_expr (HsBracket b) = pprHsBracket b
439 ppr_expr (HsBracketOut e []) = ppr e
440 ppr_expr (HsBracketOut e ps) = ppr e $$ ptext SLIT("pending") <+> ppr ps
442 ppr_expr (HsProc pat (L _ (HsCmdTop cmd _ _ _)))
443 = hsep [ptext SLIT("proc"), ppr pat, ptext SLIT("->"), ppr cmd]
445 ppr_expr (HsTick tickId vars exp)
446 = hcat [ptext SLIT("tick<"),
449 hsep (map pprHsVar vars),
452 ppr_expr (HsBinTick tickIdTrue tickIdFalse exp)
453 = hcat [ptext SLIT("bintick<"),
458 ppr exp,ptext SLIT(")")]
459 ppr_expr (HsTickPragma externalSrcLoc exp)
460 = hcat [ptext SLIT("tickpragma<"),
466 ppr_expr (HsArrApp arrow arg _ HsFirstOrderApp True)
467 = hsep [ppr_lexpr arrow, ptext SLIT("-<"), ppr_lexpr arg]
468 ppr_expr (HsArrApp arrow arg _ HsFirstOrderApp False)
469 = hsep [ppr_lexpr arg, ptext SLIT(">-"), ppr_lexpr arrow]
470 ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp True)
471 = hsep [ppr_lexpr arrow, ptext SLIT("-<<"), ppr_lexpr arg]
472 ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp False)
473 = hsep [ppr_lexpr arg, ptext SLIT(">>-"), ppr_lexpr arrow]
475 ppr_expr (HsArrForm (L _ (HsVar v)) (Just _) [arg1, arg2])
476 = sep [pprCmdArg (unLoc arg1), hsep [pprInfix v, pprCmdArg (unLoc arg2)]]
477 ppr_expr (HsArrForm op _ args)
478 = hang (ptext SLIT("(|") <> ppr_lexpr op)
479 4 (sep (map (pprCmdArg.unLoc) args) <> ptext SLIT("|)"))
481 pprCmdArg :: OutputableBndr id => HsCmdTop id -> SDoc
482 pprCmdArg (HsCmdTop cmd@(L _ (HsArrForm _ Nothing [])) _ _ _)
484 pprCmdArg (HsCmdTop cmd _ _ _)
485 = parens (ppr_lexpr cmd)
487 -- Put a var in backquotes if it's not an operator already
488 pprInfix :: Outputable name => name -> SDoc
489 pprInfix v | isOperator ppr_v = ppr_v
490 | otherwise = char '`' <> ppr_v <> char '`'
493 -- add parallel array brackets around a document
495 pa_brackets :: SDoc -> SDoc
496 pa_brackets p = ptext SLIT("[:") <> p <> ptext SLIT(":]")
499 HsSyn records exactly where the user put parens, with HsPar.
500 So generally speaking we print without adding any parens.
501 However, some code is internally generated, and in some places
502 parens are absolutely required; so for these places we use
503 pprParendExpr (but don't print double parens of course).
505 For operator applications we don't add parens, because the oprerator
506 fixities should do the job, except in debug mode (-dppr-debug) so we
507 can see the structure of the parse tree.
510 pprDebugParendExpr :: OutputableBndr id => LHsExpr id -> SDoc
511 pprDebugParendExpr expr
512 = getPprStyle (\sty ->
513 if debugStyle sty then pprParendExpr expr
516 pprParendExpr :: OutputableBndr id => LHsExpr id -> SDoc
519 pp_as_was = pprLExpr expr
520 -- Using pprLExpr makes sure that we go 'deeper'
521 -- I think that is usually (always?) right
525 HsOverLit _ -> pp_as_was
527 HsIPVar _ -> pp_as_was
528 ExplicitList _ _ -> pp_as_was
529 ExplicitPArr _ _ -> pp_as_was
530 ExplicitTuple _ _ -> pp_as_was
532 HsBracket _ -> pp_as_was
533 HsBracketOut _ [] -> pp_as_was
535 | isListCompExpr sc -> pp_as_was
536 _ -> parens pp_as_was
538 isAtomicHsExpr :: HsExpr id -> Bool -- A single token
539 isAtomicHsExpr (HsVar {}) = True
540 isAtomicHsExpr (HsLit {}) = True
541 isAtomicHsExpr (HsOverLit {}) = True
542 isAtomicHsExpr (HsIPVar {}) = True
543 isAtomicHsExpr (HsWrap _ e) = isAtomicHsExpr e
544 isAtomicHsExpr (HsPar e) = isAtomicHsExpr (unLoc e)
545 isAtomicHsExpr _ = False
548 %************************************************************************
550 \subsection{Commands (in arrow abstractions)}
552 %************************************************************************
554 We re-use HsExpr to represent these.
557 type HsCmd id = HsExpr id
559 type LHsCmd id = LHsExpr id
561 data HsArrAppType = HsHigherOrderApp | HsFirstOrderApp
564 The legal constructors for commands are:
566 = HsArrApp ... -- as above
568 | HsArrForm ... -- as above
573 | HsLam (Match id) -- kappa
575 -- the renamer turns this one into HsArrForm
576 | OpApp (HsExpr id) -- left operand
577 (HsCmd id) -- operator
578 Fixity -- Renamer adds fixity; bottom until then
579 (HsCmd id) -- right operand
581 | HsPar (HsCmd id) -- parenthesised command
584 [Match id] -- bodies are HsCmd's
587 | HsIf (HsExpr id) -- predicate
588 (HsCmd id) -- then part
589 (HsCmd id) -- else part
592 | HsLet (HsLocalBinds id) -- let(rec)
595 | HsDo (HsStmtContext Name) -- The parameterisation is unimportant
596 -- because in this context we never use
597 -- the PatGuard or ParStmt variant
598 [Stmt id] -- HsExpr's are really HsCmd's
599 PostTcType -- Type of the whole expression
602 Top-level command, introducing a new arrow.
603 This may occur inside a proc (where the stack is empty) or as an
604 argument of a command-forming operator.
607 type LHsCmdTop id = Located (HsCmdTop id)
610 = HsCmdTop (LHsCmd id)
611 [PostTcType] -- types of inputs on the command's stack
612 PostTcType -- return type of the command
613 (SyntaxTable id) -- after type checking:
614 -- names used in the command's desugaring
617 %************************************************************************
619 \subsection{Record binds}
621 %************************************************************************
624 type HsRecordBinds id = HsRecFields id (LHsExpr id)
629 %************************************************************************
631 \subsection{@Match@, @GRHSs@, and @GRHS@ datatypes}
633 %************************************************************************
635 @Match@es are sets of pattern bindings and right hand sides for
636 functions, patterns or case branches. For example, if a function @g@
642 then \tr{g} has two @Match@es: @(x,y) = y@ and @((x:ys),y) = y+1@.
644 It is always the case that each element of an @[Match]@ list has the
645 same number of @pats@s inside it. This corresponds to saying that
646 a function defined by pattern matching must have the same number of
647 patterns in each equation.
652 [LMatch id] -- The alternatives
653 PostTcType -- The type is the type of the entire group
654 -- t1 -> ... -> tn -> tr
655 -- where there are n patterns
657 type LMatch id = Located (Match id)
661 [LPat id] -- The patterns
662 (Maybe (LHsType id)) -- A type signature for the result of the match
663 -- Nothing after typechecking
666 matchGroupArity :: MatchGroup id -> Arity
667 matchGroupArity (MatchGroup [] _)
668 = panic "matchGroupArity" -- MatchGroup is never empty
669 matchGroupArity (MatchGroup (match:matches) _)
670 = ASSERT( all ((== n_pats) . length . hsLMatchPats) matches )
671 -- Assertion just checks that all the matches have the same number of pats
674 n_pats = length (hsLMatchPats match)
676 hsLMatchPats :: LMatch id -> [LPat id]
677 hsLMatchPats (L _ (Match pats _ _)) = pats
679 -- GRHSs are used both for pattern bindings and for Matches
681 = GRHSs [LGRHS id] -- Guarded RHSs
682 (HsLocalBinds id) -- The where clause
684 type LGRHS id = Located (GRHS id)
686 data GRHS id = GRHS [LStmt id] -- Guards
687 (LHsExpr id) -- Right hand side
690 We know the list must have at least one @Match@ in it.
693 pprMatches :: (OutputableBndr idL, OutputableBndr idR) => HsMatchContext idL -> MatchGroup idR -> SDoc
694 pprMatches ctxt (MatchGroup matches _)
695 = vcat (map (pprMatch ctxt) (map unLoc matches))
696 -- Don't print the type; it's only a place-holder before typechecking
698 -- Exported to HsBinds, which can't see the defn of HsMatchContext
699 pprFunBind :: (OutputableBndr idL, OutputableBndr idR) => idL -> Bool -> MatchGroup idR -> SDoc
700 pprFunBind fun inf matches = pprMatches (FunRhs fun inf) matches
702 -- Exported to HsBinds, which can't see the defn of HsMatchContext
703 pprPatBind :: (OutputableBndr bndr, OutputableBndr id)
704 => LPat bndr -> GRHSs id -> SDoc
705 pprPatBind pat ty@(grhss)
706 = sep [ppr pat, nest 4 (pprGRHSs (PatBindRhs `asTypeOf` idType ty) grhss)]
707 --avoid using PatternSignatures for stage1 code portability
708 where idType :: GRHSs id -> HsMatchContext id; idType = undefined
711 pprMatch :: (OutputableBndr idL, OutputableBndr idR) => HsMatchContext idL -> Match idR -> SDoc
712 pprMatch ctxt (Match pats maybe_ty grhss)
713 = herald <+> sep [sep (map ppr other_pats),
715 nest 2 (pprGRHSs ctxt grhss)]
720 | not is_infix -> (ppr fun, pats)
722 -- Not pprBndr; the AbsBinds will
723 -- have printed the signature
725 | null pats3 -> (pp_infix, [])
728 | otherwise -> (parens pp_infix, pats3)
731 (pat1:pat2:pats3) = pats
732 pp_infix = ppr pat1 <+> ppr fun <+> ppr pat2
734 LambdaExpr -> (char '\\', pats)
737 ppr_maybe_ty = case maybe_ty of
738 Just ty -> dcolon <+> ppr ty
742 pprGRHSs :: (OutputableBndr idL, OutputableBndr idR)
743 => HsMatchContext idL -> GRHSs idR -> SDoc
744 pprGRHSs ctxt (GRHSs grhss binds)
745 = vcat (map (pprGRHS ctxt . unLoc) grhss)
746 $$ if isEmptyLocalBinds binds then empty
747 else text "where" $$ nest 4 (pprBinds binds)
749 pprGRHS :: (OutputableBndr idL, OutputableBndr idR)
750 => HsMatchContext idL -> GRHS idR -> SDoc
752 pprGRHS ctxt (GRHS [] expr)
755 pprGRHS ctxt (GRHS guards expr)
756 = sep [char '|' <+> interpp'SP guards, pp_rhs ctxt expr]
758 pp_rhs :: OutputableBndr idR => HsMatchContext idL -> LHsExpr idR -> SDoc
759 pp_rhs ctxt rhs = matchSeparator ctxt <+> pprDeeper (ppr rhs)
762 %************************************************************************
764 \subsection{Do stmts and list comprehensions}
766 %************************************************************************
769 type LStmt id = Located (StmtLR id id)
770 type LStmtLR idL idR = Located (StmtLR idL idR)
772 type Stmt id = StmtLR id id
774 data GroupByClause id
775 = GroupByNothing (LHsExpr id) -- Using expression, i.e.
776 -- "then group using f" ==> GroupByNothing f
777 | GroupBySomething (Either (LHsExpr id) (SyntaxExpr id)) (LHsExpr id)
778 -- "then group using f by e" ==> GroupBySomething (Left f) e
779 -- "then group by e" ==> GroupBySomething (Right _) e: in
780 -- this case the expression is filled
783 -- The SyntaxExprs in here are used *only* for do-notation, which
784 -- has rebindable syntax. Otherwise they are unused.
786 = BindStmt (LPat idL)
788 (SyntaxExpr idR) -- The (>>=) operator
789 (SyntaxExpr idR) -- The fail operator
790 -- The fail operator is noSyntaxExpr
791 -- if the pattern match can't fail
793 | ExprStmt (LHsExpr idR)
794 (SyntaxExpr idR) -- The (>>) operator
795 PostTcType -- Element type of the RHS (used for arrows)
797 | LetStmt (HsLocalBindsLR idL idR)
799 -- ParStmts only occur in a list comprehension
800 | ParStmt [([LStmt idL], [idR])]
801 -- After renaming, the ids are the binders bound by the stmts and used
804 | TransformStmt ([LStmt idL], [idR]) (LHsExpr idR) (Maybe (LHsExpr idR))
805 -- After renaming, the IDs are the binders occurring within this
806 -- transform statement that are used after it
807 -- "qs, then f by e" ==> TransformStmt (qs, binders) f (Just e)
808 -- "qs, then f" ==> TransformStmt (qs, binders) f Nothing
810 | GroupStmt ([LStmt idL], [(idR, idR)]) (GroupByClause idR)
811 -- After renaming, the IDs are the binders occurring within this
812 -- transform statement that are used after it which are paired with
813 -- the names which they group over in statements
815 -- Recursive statement (see Note [RecStmt] below)
816 | RecStmt [LStmtLR idL idR]
817 --- The next two fields are only valid after renaming
818 [idR] -- The ids are a subset of the variables bound by the
819 -- stmts that are used in stmts that follow the RecStmt
821 [idR] -- Ditto, but these variables are the "recursive" ones,
822 -- that are used before they are bound in the stmts of
823 -- the RecStmt. From a type-checking point of view,
824 -- these ones have to be monomorphic
826 --- These fields are only valid after typechecking
827 [PostTcExpr] -- These expressions correspond 1-to-1 with
828 -- the "recursive" [id], and are the
829 -- expressions that should be returned by
831 -- They may not quite be the Ids themselves,
832 -- because the Id may be *polymorphic*, but
833 -- the returned thing has to be *monomorphic*.
834 (DictBinds idR) -- Method bindings of Ids bound by the
835 -- RecStmt, and used afterwards
838 ExprStmts are a bit tricky, because what they mean
839 depends on the context. Consider the following contexts:
841 A do expression of type (m res_ty)
842 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
843 * ExprStmt E any_ty: do { ....; E; ... }
845 Translation: E >> ...
847 A list comprehensions of type [elt_ty]
848 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
849 * ExprStmt E Bool: [ .. | .... E ]
851 [ .. | .... | ..., E | ... ]
853 Translation: if E then fail else ...
855 A guard list, guarding a RHS of type rhs_ty
856 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
857 * ExprStmt E Bool: f x | ..., E, ... = ...rhs...
859 Translation: if E then fail else ...
861 Array comprehensions are handled like list comprehensions -=chak
868 , RecStmt [a::forall a. a -> a, b]
870 [ BindStmt b (return x)
876 Here, the RecStmt binds a,b,c; but
877 - Only a,b are used in the stmts *following* the RecStmt,
878 This 'a' is *polymorphic'
879 - Only a,c are used in the stmts *inside* the RecStmt
880 *before* their bindings
881 This 'a' is monomorphic
883 Nota Bene: the two a's have different types, even though they
888 instance (OutputableBndr idL, OutputableBndr idR) => Outputable (StmtLR idL idR) where
889 ppr stmt = pprStmt stmt
891 pprStmt :: (OutputableBndr idL, OutputableBndr idR) => (StmtLR idL idR) -> SDoc
892 pprStmt (BindStmt pat expr _ _) = hsep [ppr pat, ptext SLIT("<-"), ppr expr]
893 pprStmt (LetStmt binds) = hsep [ptext SLIT("let"), pprBinds binds]
894 pprStmt (ExprStmt expr _ _) = ppr expr
895 pprStmt (ParStmt stmtss) = hsep (map doStmts stmtss)
896 where doStmts stmts = ptext SLIT("| ") <> ppr stmts
897 pprStmt (TransformStmt (stmts, _) usingExpr maybeByExpr)
898 = (hsep [stmtsDoc, ptext SLIT("then"), ppr usingExpr, byExprDoc])
899 where stmtsDoc = interpp'SP stmts
900 byExprDoc = maybe empty (\byExpr -> hsep [ptext SLIT("by"), ppr byExpr]) maybeByExpr
901 pprStmt (GroupStmt (stmts, _) groupByClause) = (hsep [stmtsDoc, ptext SLIT("then group"), pprGroupByClause groupByClause])
902 where stmtsDoc = interpp'SP stmts
903 pprStmt (RecStmt segment _ _ _ _) = ptext SLIT("rec") <+> braces (vcat (map ppr segment))
905 pprGroupByClause :: (OutputableBndr id) => GroupByClause id -> SDoc
906 pprGroupByClause (GroupByNothing usingExpr) = hsep [ptext SLIT("using"), ppr usingExpr]
907 pprGroupByClause (GroupBySomething eitherUsingExpr byExpr) = hsep [ptext SLIT("by"), ppr byExpr, usingExprDoc]
908 where usingExprDoc = either (\usingExpr -> hsep [ptext SLIT("using"), ppr usingExpr]) (const empty) eitherUsingExpr
910 pprDo :: OutputableBndr id => HsStmtContext any -> [LStmt id] -> LHsExpr id -> SDoc
911 pprDo DoExpr stmts body = ptext SLIT("do") <+> pprDeeperList vcat (map ppr stmts ++ [ppr body])
912 pprDo (MDoExpr _) stmts body = ptext SLIT("mdo") <+> pprDeeperList vcat (map ppr stmts ++ [ppr body])
913 pprDo ListComp stmts body = pprComp brackets stmts body
914 pprDo PArrComp stmts body = pprComp pa_brackets stmts body
915 pprDo _ _ _ = panic "pprDo" -- PatGuard, ParStmtCxt
917 pprComp :: OutputableBndr id => (SDoc -> SDoc) -> [LStmt id] -> LHsExpr id -> SDoc
918 pprComp brack quals body
920 hang (ppr body <+> char '|')
924 %************************************************************************
926 Template Haskell quotation brackets
928 %************************************************************************
931 data HsSplice id = HsSplice -- $z or $(f 4)
932 id -- The id is just a unique name to
933 (LHsExpr id) -- identify this splice point
935 instance OutputableBndr id => Outputable (HsSplice id) where
938 pprSplice :: OutputableBndr id => HsSplice id -> SDoc
939 pprSplice (HsSplice n e)
940 = char '$' <> ifPprDebug (brackets (ppr n)) <> pprParendExpr e
943 data HsBracket id = ExpBr (LHsExpr id) -- [| expr |]
944 | PatBr (LPat id) -- [p| pat |]
945 | DecBr (HsGroup id) -- [d| decls |]
946 | TypBr (LHsType id) -- [t| type |]
947 | VarBr id -- 'x, ''T
949 instance OutputableBndr id => Outputable (HsBracket id) where
953 pprHsBracket :: OutputableBndr id => HsBracket id -> SDoc
954 pprHsBracket (ExpBr e) = thBrackets empty (ppr e)
955 pprHsBracket (PatBr p) = thBrackets (char 'p') (ppr p)
956 pprHsBracket (DecBr d) = thBrackets (char 'd') (ppr d)
957 pprHsBracket (TypBr t) = thBrackets (char 't') (ppr t)
958 pprHsBracket (VarBr n) = char '\'' <> ppr n
959 -- Infelicity: can't show ' vs '', because
960 -- we can't ask n what its OccName is, because the
961 -- pretty-printer for HsExpr doesn't ask for NamedThings
962 -- But the pretty-printer for names will show the OccName class
964 thBrackets :: SDoc -> SDoc -> SDoc
965 thBrackets pp_kind pp_body = char '[' <> pp_kind <> char '|' <+>
966 pp_body <+> ptext SLIT("|]")
969 %************************************************************************
971 \subsection{Enumerations and list comprehensions}
973 %************************************************************************
978 | FromThen (LHsExpr id)
980 | FromTo (LHsExpr id)
982 | FromThenTo (LHsExpr id)
988 instance OutputableBndr id => Outputable (ArithSeqInfo id) where
989 ppr (From e1) = hcat [ppr e1, pp_dotdot]
990 ppr (FromThen e1 e2) = hcat [ppr e1, comma, space, ppr e2, pp_dotdot]
991 ppr (FromTo e1 e3) = hcat [ppr e1, pp_dotdot, ppr e3]
992 ppr (FromThenTo e1 e2 e3)
993 = hcat [ppr e1, comma, space, ppr e2, pp_dotdot, ppr e3]
996 pp_dotdot = ptext SLIT(" .. ")
1000 %************************************************************************
1002 \subsection{HsMatchCtxt}
1004 %************************************************************************
1007 data HsMatchContext id -- Context of a Match
1008 = FunRhs id Bool -- Function binding for f; True <=> written infix
1009 | CaseAlt -- Guard on a case alternative
1010 | LambdaExpr -- Pattern of a lambda
1011 | ProcExpr -- Pattern of a proc
1012 | PatBindRhs -- Pattern binding
1013 | RecUpd -- Record update [used only in DsExpr to
1014 -- tell matchWrapper what sort of
1015 -- runtime error message to generate]
1016 | StmtCtxt (HsStmtContext id) -- Pattern of a do-stmt or list comprehension
1019 data HsStmtContext id
1022 | MDoExpr PostTcTable -- Recursive do-expression
1023 -- (tiresomely, it needs table
1024 -- of its return/bind ops)
1025 | PArrComp -- Parallel array comprehension
1026 | PatGuard (HsMatchContext id) -- Pattern guard for specified thing
1027 | ParStmtCtxt (HsStmtContext id) -- A branch of a parallel stmt
1028 | TransformStmtCtxt (HsStmtContext id) -- A branch of a transform stmt
1032 isDoExpr :: HsStmtContext id -> Bool
1033 isDoExpr DoExpr = True
1034 isDoExpr (MDoExpr _) = True
1037 isListCompExpr :: HsStmtContext id -> Bool
1038 isListCompExpr ListComp = True
1039 isListCompExpr PArrComp = True
1040 isListCompExpr _ = False
1044 matchSeparator :: HsMatchContext id -> SDoc
1045 matchSeparator (FunRhs {}) = ptext SLIT("=")
1046 matchSeparator CaseAlt = ptext SLIT("->")
1047 matchSeparator LambdaExpr = ptext SLIT("->")
1048 matchSeparator ProcExpr = ptext SLIT("->")
1049 matchSeparator PatBindRhs = ptext SLIT("=")
1050 matchSeparator (StmtCtxt _) = ptext SLIT("<-")
1051 matchSeparator RecUpd = panic "unused"
1055 pprMatchContext :: Outputable id => HsMatchContext id -> SDoc
1056 pprMatchContext (FunRhs fun _) = ptext SLIT("the definition of")
1057 <+> quotes (ppr fun)
1058 pprMatchContext CaseAlt = ptext SLIT("a case alternative")
1059 pprMatchContext RecUpd = ptext SLIT("a record-update construct")
1060 pprMatchContext PatBindRhs = ptext SLIT("a pattern binding")
1061 pprMatchContext LambdaExpr = ptext SLIT("a lambda abstraction")
1062 pprMatchContext ProcExpr = ptext SLIT("an arrow abstraction")
1063 pprMatchContext (StmtCtxt ctxt) = ptext SLIT("a pattern binding in")
1064 $$ pprStmtContext ctxt
1066 pprStmtContext :: Outputable id => HsStmtContext id -> SDoc
1067 pprStmtContext (ParStmtCtxt c)
1068 = sep [ptext SLIT("a parallel branch of"), pprStmtContext c]
1069 pprStmtContext (TransformStmtCtxt c)
1070 = sep [ptext SLIT("a transformed branch of"), pprStmtContext c]
1071 pprStmtContext (PatGuard ctxt)
1072 = ptext SLIT("a pattern guard for") $$ pprMatchContext ctxt
1073 pprStmtContext DoExpr = ptext SLIT("a 'do' expression")
1074 pprStmtContext (MDoExpr _) = ptext SLIT("an 'mdo' expression")
1075 pprStmtContext ListComp = ptext SLIT("a list comprehension")
1076 pprStmtContext PArrComp = ptext SLIT("an array comprehension")
1079 pprMatchRhsContext (FunRhs fun) = ptext SLIT("a right-hand side of function") <+> quotes (ppr fun)
1080 pprMatchRhsContext CaseAlt = ptext SLIT("the body of a case alternative")
1081 pprMatchRhsContext PatBindRhs = ptext SLIT("the right-hand side of a pattern binding")
1082 pprMatchRhsContext LambdaExpr = ptext SLIT("the body of a lambda")
1083 pprMatchRhsContext ProcExpr = ptext SLIT("the body of a proc")
1084 pprMatchRhsContext other = panic "pprMatchRhsContext" -- RecUpd, StmtCtxt
1086 -- Used for the result statement of comprehension
1087 -- e.g. the 'e' in [ e | ... ]
1088 -- or the 'r' in f x = r
1089 pprStmtResultContext (PatGuard ctxt) = pprMatchRhsContext ctxt
1090 pprStmtResultContext other = ptext SLIT("the result of") <+> pprStmtContext other
1093 -- Used to generate the string for a *runtime* error message
1094 matchContextErrString :: Outputable id => HsMatchContext id -> String
1095 matchContextErrString (FunRhs fun _) = "function " ++ showSDoc (ppr fun)
1096 matchContextErrString CaseAlt = "case"
1097 matchContextErrString PatBindRhs = "pattern binding"
1098 matchContextErrString RecUpd = "record update"
1099 matchContextErrString LambdaExpr = "lambda"
1100 matchContextErrString ProcExpr = "proc"
1101 matchContextErrString (StmtCtxt (ParStmtCtxt c)) = matchContextErrString (StmtCtxt c)
1102 matchContextErrString (StmtCtxt (TransformStmtCtxt c)) = matchContextErrString (StmtCtxt c)
1103 matchContextErrString (StmtCtxt (PatGuard _)) = "pattern guard"
1104 matchContextErrString (StmtCtxt DoExpr) = "'do' expression"
1105 matchContextErrString (StmtCtxt (MDoExpr _)) = "'mdo' expression"
1106 matchContextErrString (StmtCtxt ListComp) = "list comprehension"
1107 matchContextErrString (StmtCtxt PArrComp) = "array comprehension"