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"
31 %************************************************************************
33 \subsection{Expressions proper}
35 %************************************************************************
38 type LHsExpr id = Located (HsExpr id)
40 -------------------------
41 -- PostTcExpr is an evidence expression attached to the
42 -- syntax tree by the type checker (c.f. postTcType)
43 -- We use a PostTcTable where there are a bunch of pieces of
44 -- evidence, more than is convenient to keep individually
45 type PostTcExpr = HsExpr Id
46 type PostTcTable = [(Name, Id)]
48 noPostTcExpr :: PostTcExpr
49 noPostTcExpr = HsLit (HsString FSLIT("noPostTcExpr"))
51 noPostTcTable :: PostTcTable
54 -------------------------
55 -- SyntaxExpr is like PostTcExpr, but it's filled in a little earlier,
56 -- by the renamer. It's used for rebindable syntax.
57 -- E.g. (>>=) is filled in before the renamer by the appropriate Name
58 -- for (>>=), and then instantiated by the type checker with its
61 type SyntaxExpr id = HsExpr id
63 noSyntaxExpr :: SyntaxExpr id -- Before renaming, and sometimes after,
64 -- (if the syntax slot makes no sense)
65 noSyntaxExpr = HsLit (HsString FSLIT("noSyntaxExpr"))
68 type SyntaxTable id = [(Name, SyntaxExpr id)]
69 -- *** Currently used only for CmdTop (sigh) ***
70 -- * Before the renamer, this list is noSyntaxTable
72 -- * After the renamer, it takes the form [(std_name, HsVar actual_name)]
73 -- For example, for the 'return' op of a monad
74 -- normal case: (GHC.Base.return, HsVar GHC.Base.return)
75 -- with rebindable syntax: (GHC.Base.return, return_22)
76 -- where return_22 is whatever "return" is in scope
78 -- * After the type checker, it takes the form [(std_name, <expression>)]
79 -- where <expression> is the evidence for the method
81 noSyntaxTable :: SyntaxTable id
85 -------------------------
87 = HsVar id -- variable
88 | HsIPVar (IPName id) -- implicit parameter
89 | HsOverLit (HsOverLit id) -- Overloaded literals
90 | HsLit HsLit -- Simple (non-overloaded) literals
92 | HsLam (MatchGroup id) -- Currently always a single match
94 | HsApp (LHsExpr id) -- Application
97 -- Operator applications:
98 -- NB Bracketed ops such as (+) come out as Vars.
100 -- NB We need an expr for the operator in an OpApp/Section since
101 -- the typechecker may need to apply the operator to a few types.
103 | OpApp (LHsExpr id) -- left operand
104 (LHsExpr id) -- operator
105 Fixity -- Renamer adds fixity; bottom until then
106 (LHsExpr id) -- right operand
108 | NegApp (LHsExpr id) -- negated expr
109 (SyntaxExpr id) -- Name of 'negate'
111 | HsPar (LHsExpr id) -- parenthesised expr
113 | SectionL (LHsExpr id) -- operand
114 (LHsExpr id) -- operator
115 | SectionR (LHsExpr id) -- operator
116 (LHsExpr id) -- operand
118 | HsCase (LHsExpr id)
121 | HsIf (LHsExpr id) -- predicate
122 (LHsExpr id) -- then part
123 (LHsExpr id) -- else part
125 | HsLet (HsLocalBinds id) -- let(rec)
128 | HsDo (HsStmtContext Name) -- The parameterisation is unimportant
129 -- because in this context we never use
130 -- the PatGuard or ParStmt variant
131 [LStmt id] -- "do":one or more stmts
132 (LHsExpr id) -- The body; the last expression in the 'do'
133 -- of [ body | ... ] in a list comp
134 PostTcType -- Type of the whole expression
136 | ExplicitList -- syntactic list
137 PostTcType -- Gives type of components of list
140 | ExplicitPArr -- syntactic parallel array: [:e1, ..., en:]
141 PostTcType -- type of elements of the parallel array
144 | ExplicitTuple -- tuple
146 -- NB: Unit is ExplicitTuple []
147 -- for tuples, we can get the types
148 -- direct from the components
152 -- Record construction
153 | RecordCon (Located id) -- The constructor. After type checking
154 -- it's the dataConWrapId of the constructor
155 PostTcExpr -- Data con Id applied to type args
159 | RecordUpd (LHsExpr id)
161 PostTcType -- Type of *input* record
162 PostTcType -- Type of *result* record (may differ from
163 -- type of input record)
165 | ExprWithTySig -- e :: type
169 | ExprWithTySigOut -- TRANSLATION
171 (LHsType Name) -- Retain the signature for round-tripping purposes
173 | ArithSeq -- arithmetic sequence
177 | PArrSeq -- arith. sequence for parallel array
178 PostTcExpr -- [:e1..e2:] or [:e1, e2..e3:]
181 | HsSCC FastString -- "set cost centre" (_scc_) annotation
182 (LHsExpr id) -- expr whose cost is to be measured
184 | HsCoreAnn FastString -- hdaume: core annotation
187 -----------------------------------------------------------
188 -- MetaHaskell Extensions
190 | HsBracket (HsBracket id)
192 | HsBracketOut (HsBracket Name) -- Output of the type checker is the *original*
193 [PendingSplice] -- renamed expression, plus *typechecked* splices
194 -- to be pasted back in by the desugarer
196 | HsSpliceE (HsSplice id)
198 -----------------------------------------------------------
199 -- Arrow notation extension
201 | HsProc (LPat id) -- arrow abstraction, proc
202 (LHsCmdTop id) -- body of the abstraction
203 -- always has an empty stack
205 ---------------------------------------
206 -- The following are commands, not expressions proper
208 | HsArrApp -- Arrow tail, or arrow application (f -< arg)
209 (LHsExpr id) -- arrow expression, f
210 (LHsExpr id) -- input expression, arg
211 PostTcType -- type of the arrow expressions f,
212 -- of the form a t t', where arg :: t
213 HsArrAppType -- higher-order (-<<) or first-order (-<)
214 Bool -- True => right-to-left (f -< arg)
215 -- False => left-to-right (arg >- f)
217 | HsArrForm -- Command formation, (| e cmd1 .. cmdn |)
218 (LHsExpr id) -- the operator
219 -- after type-checking, a type abstraction to be
220 -- applied to the type of the local environment tuple
221 (Maybe Fixity) -- fixity (filled in by the renamer), for forms that
222 -- were converted from OpApp's by the renamer
223 [LHsCmdTop id] -- argument commands
226 ---------------------------------------
227 -- Haskell program coverage (Hpc) Support
230 Int -- module-local tick number
231 [id] -- variables in scope
232 (LHsExpr id) -- sub-expression
235 Int -- module-local tick number for True
236 Int -- module-local tick number for False
237 (LHsExpr id) -- sub-expression
239 | HsTickPragma -- A pragma introduced tick
240 (FastString,(Int,Int),(Int,Int)) -- external span for this tick
243 ---------------------------------------
244 -- These constructors only appear temporarily in the parser.
245 -- The renamer translates them into the Right Thing.
247 | EWildPat -- wildcard
249 | EAsPat (Located id) -- as pattern
252 | ELazyPat (LHsExpr id) -- ~ pattern
254 | HsType (LHsType id) -- Explicit type argument; e.g f {| Int |} x y
256 ---------------------------------------
257 -- Finally, HsWrap appears only in typechecker output
259 | HsWrap HsWrapper -- TRANSLATION
262 type PendingSplice = (Name, LHsExpr Id) -- Typechecked splices, waiting to be
263 -- pasted back in by the desugarer
266 A @Dictionary@, unless of length 0 or 1, becomes a tuple. A
267 @ClassDictLam dictvars methods expr@ is, therefore:
269 \ x -> case x of ( dictvars-and-methods-tuple ) -> expr
273 instance OutputableBndr id => Outputable (HsExpr id) where
274 ppr expr = pprExpr expr
278 -- pprExpr and pprLExpr call pprDeeper;
279 -- the underscore versions do not
280 pprExpr :: OutputableBndr id => HsExpr id -> SDoc
281 pprExpr e = pprDeeper (ppr_expr e)
283 pprLExpr :: OutputableBndr id => LHsExpr id -> SDoc
284 pprLExpr e = pprDeeper (ppr_expr (unLoc e))
286 pprBinds :: OutputableBndr id => HsLocalBinds id -> SDoc
287 pprBinds b = pprDeeper (ppr b)
289 ppr_lexpr :: OutputableBndr id => LHsExpr id -> SDoc
290 ppr_lexpr e = ppr_expr (unLoc e)
292 ppr_expr (HsVar v) = pprHsVar v
293 ppr_expr (HsIPVar v) = ppr v
294 ppr_expr (HsLit lit) = ppr lit
295 ppr_expr (HsOverLit lit) = ppr lit
296 ppr_expr (HsPar e) = parens (ppr_lexpr e)
298 ppr_expr (HsCoreAnn s e)
299 = vcat [ptext SLIT("HsCoreAnn") <+> ftext s, ppr_lexpr e]
301 ppr_expr (HsApp e1 e2)
302 = let (fun, args) = collect_args e1 [e2] in
303 hang (ppr_lexpr fun) 2 (sep (map pprParendExpr args))
305 collect_args (L _ (HsApp fun arg)) args = collect_args fun (arg:args)
306 collect_args fun args = (fun, args)
308 ppr_expr (OpApp e1 op fixity e2)
310 HsVar v -> pp_infixly v
313 pp_e1 = pprParendExpr e1 -- Add parens to make precedence clear
314 pp_e2 = pprParendExpr e2
317 = hang (ppr op) 2 (sep [pp_e1, pp_e2])
320 = sep [nest 2 pp_e1, pprInfix v, nest 2 pp_e2]
322 ppr_expr (NegApp e _) = char '-' <+> pprParendExpr e
324 ppr_expr (SectionL expr op)
326 HsVar v -> pp_infixly v
329 pp_expr = pprParendExpr expr
331 pp_prefixly = hang (hsep [text " \\ x_ ->", ppr op])
332 4 (hsep [pp_expr, ptext SLIT("x_ )")])
333 pp_infixly v = parens (sep [pp_expr, pprInfix v])
335 ppr_expr (SectionR op expr)
337 HsVar v -> pp_infixly v
340 pp_expr = pprParendExpr expr
342 pp_prefixly = hang (hsep [text "( \\ x_ ->", ppr op, ptext SLIT("x_")])
343 4 ((<>) pp_expr rparen)
345 = parens (sep [pprInfix v, pp_expr])
347 ppr_expr (HsLam matches)
348 = pprMatches LambdaExpr matches
350 ppr_expr (HsCase expr matches)
351 = sep [ sep [ptext SLIT("case"), nest 4 (ppr expr), ptext SLIT("of")],
352 nest 2 (pprMatches CaseAlt matches) ]
354 ppr_expr (HsIf e1 e2 e3)
355 = sep [hsep [ptext SLIT("if"), nest 2 (ppr e1), ptext SLIT("then")],
360 -- special case: let ... in let ...
361 ppr_expr (HsLet binds expr@(L _ (HsLet _ _)))
362 = sep [hang (ptext SLIT("let")) 2 (hsep [pprBinds binds, ptext SLIT("in")]),
365 ppr_expr (HsLet binds expr)
366 = sep [hang (ptext SLIT("let")) 2 (pprBinds binds),
367 hang (ptext SLIT("in")) 2 (ppr expr)]
369 ppr_expr (HsDo do_or_list_comp stmts body _) = pprDo do_or_list_comp stmts body
371 ppr_expr (ExplicitList _ exprs)
372 = brackets (pprDeeperList fsep (punctuate comma (map ppr_lexpr exprs)))
374 ppr_expr (ExplicitPArr _ exprs)
375 = pa_brackets (pprDeeperList fsep (punctuate comma (map ppr_lexpr exprs)))
377 ppr_expr (ExplicitTuple exprs boxity)
378 = tupleParens boxity (pprDeeperList sep (punctuate comma (map ppr_lexpr exprs)))
380 ppr_expr (RecordCon con_id con_expr rbinds)
381 = pp_rbinds (ppr con_id) rbinds
383 ppr_expr (RecordUpd aexp rbinds _ _)
384 = pp_rbinds (pprParendExpr aexp) rbinds
386 ppr_expr (ExprWithTySig expr sig)
387 = hang (nest 2 (ppr_lexpr expr) <+> dcolon)
389 ppr_expr (ExprWithTySigOut expr sig)
390 = hang (nest 2 (ppr_lexpr expr) <+> dcolon)
393 ppr_expr (ArithSeq expr info) = brackets (ppr info)
394 ppr_expr (PArrSeq expr info) = pa_brackets (ppr info)
396 ppr_expr EWildPat = char '_'
397 ppr_expr (ELazyPat e) = char '~' <> pprParendExpr e
398 ppr_expr (EAsPat v e) = ppr v <> char '@' <> pprParendExpr e
400 ppr_expr (HsSCC lbl expr)
401 = sep [ ptext SLIT("_scc_") <+> doubleQuotes (ftext lbl), pprParendExpr expr ]
403 ppr_expr (HsWrap co_fn e) = pprHsWrapper (ppr_expr e) co_fn
404 ppr_expr (HsType id) = ppr id
406 ppr_expr (HsSpliceE s) = pprSplice s
407 ppr_expr (HsBracket b) = pprHsBracket b
408 ppr_expr (HsBracketOut e []) = ppr e
409 ppr_expr (HsBracketOut e ps) = ppr e $$ ptext SLIT("pending") <+> ppr ps
411 ppr_expr (HsProc pat (L _ (HsCmdTop cmd _ _ _)))
412 = hsep [ptext SLIT("proc"), ppr pat, ptext SLIT("->"), ppr cmd]
414 ppr_expr (HsTick tickId vars exp)
415 = hcat [ptext SLIT("tick<"), ppr tickId,ptext SLIT(">("), hsep (map pprHsVar vars), ppr exp,ptext SLIT(")")]
416 ppr_expr (HsBinTick tickIdTrue tickIdFalse exp)
417 = hcat [ptext SLIT("bintick<"),
422 ppr exp,ptext SLIT(")")]
423 ppr_expr (HsTickPragma externalSrcLoc exp)
424 = hcat [ptext SLIT("tickpragma<"), ppr externalSrcLoc,ptext SLIT(">("), ppr exp,ptext SLIT(")")]
426 ppr_expr (HsArrApp arrow arg _ HsFirstOrderApp True)
427 = hsep [ppr_lexpr arrow, ptext SLIT("-<"), ppr_lexpr arg]
428 ppr_expr (HsArrApp arrow arg _ HsFirstOrderApp False)
429 = hsep [ppr_lexpr arg, ptext SLIT(">-"), ppr_lexpr arrow]
430 ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp True)
431 = hsep [ppr_lexpr arrow, ptext SLIT("-<<"), ppr_lexpr arg]
432 ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp False)
433 = hsep [ppr_lexpr arg, ptext SLIT(">>-"), ppr_lexpr arrow]
435 ppr_expr (HsArrForm (L _ (HsVar v)) (Just _) [arg1, arg2])
436 = sep [pprCmdArg (unLoc arg1), hsep [pprInfix v, pprCmdArg (unLoc arg2)]]
437 ppr_expr (HsArrForm op _ args)
438 = hang (ptext SLIT("(|") <> ppr_lexpr op)
439 4 (sep (map (pprCmdArg.unLoc) args) <> ptext SLIT("|)"))
441 pprCmdArg :: OutputableBndr id => HsCmdTop id -> SDoc
442 pprCmdArg (HsCmdTop cmd@(L _ (HsArrForm _ Nothing [])) _ _ _)
444 pprCmdArg (HsCmdTop cmd _ _ _)
445 = parens (ppr_lexpr cmd)
447 -- Put a var in backquotes if it's not an operator already
448 pprInfix :: Outputable name => name -> SDoc
449 pprInfix v | isOperator ppr_v = ppr_v
450 | otherwise = char '`' <> ppr_v <> char '`'
454 -- add parallel array brackets around a document
456 pa_brackets :: SDoc -> SDoc
457 pa_brackets p = ptext SLIT("[:") <> p <> ptext SLIT(":]")
460 Parenthesize unless very simple:
462 pprParendExpr :: OutputableBndr id => LHsExpr id -> SDoc
465 pp_as_was = pprLExpr expr
466 -- Using pprLExpr makes sure that we go 'deeper'
467 -- I think that is usually (always?) right
474 HsIPVar _ -> pp_as_was
475 ExplicitList _ _ -> pp_as_was
476 ExplicitPArr _ _ -> pp_as_was
477 ExplicitTuple _ _ -> pp_as_was
479 HsBracket _ -> pp_as_was
480 HsBracketOut _ [] -> pp_as_was
481 _ -> parens pp_as_was
484 %************************************************************************
486 \subsection{Commands (in arrow abstractions)}
488 %************************************************************************
490 We re-use HsExpr to represent these.
493 type HsCmd id = HsExpr id
495 type LHsCmd id = LHsExpr id
497 data HsArrAppType = HsHigherOrderApp | HsFirstOrderApp
500 The legal constructors for commands are:
502 = HsArrApp ... -- as above
504 | HsArrForm ... -- as above
509 | HsLam (Match id) -- kappa
511 -- the renamer turns this one into HsArrForm
512 | OpApp (HsExpr id) -- left operand
513 (HsCmd id) -- operator
514 Fixity -- Renamer adds fixity; bottom until then
515 (HsCmd id) -- right operand
517 | HsPar (HsCmd id) -- parenthesised command
520 [Match id] -- bodies are HsCmd's
523 | HsIf (HsExpr id) -- predicate
524 (HsCmd id) -- then part
525 (HsCmd id) -- else part
528 | HsLet (HsLocalBinds id) -- let(rec)
531 | HsDo (HsStmtContext Name) -- The parameterisation is unimportant
532 -- because in this context we never use
533 -- the PatGuard or ParStmt variant
534 [Stmt id] -- HsExpr's are really HsCmd's
535 PostTcType -- Type of the whole expression
538 Top-level command, introducing a new arrow.
539 This may occur inside a proc (where the stack is empty) or as an
540 argument of a command-forming operator.
543 type LHsCmdTop id = Located (HsCmdTop id)
546 = HsCmdTop (LHsCmd id)
547 [PostTcType] -- types of inputs on the command's stack
548 PostTcType -- return type of the command
550 -- after type checking:
551 -- names used in the command's desugaring
554 %************************************************************************
556 \subsection{Record binds}
558 %************************************************************************
561 data HsRecordBinds id = HsRecordBinds [(Located id, LHsExpr id)]
563 recBindFields :: HsRecordBinds id -> [id]
564 recBindFields (HsRecordBinds rbinds) = [unLoc field | (field,_) <- rbinds]
566 pp_rbinds :: OutputableBndr id => SDoc -> HsRecordBinds id -> SDoc
567 pp_rbinds thing (HsRecordBinds rbinds)
569 4 (braces (pprDeeperList sep (punctuate comma (map (pp_rbind) rbinds))))
571 pp_rbind (v, e) = hsep [pprBndr LetBind (unLoc v), char '=', ppr e]
576 %************************************************************************
578 \subsection{@Match@, @GRHSs@, and @GRHS@ datatypes}
580 %************************************************************************
582 @Match@es are sets of pattern bindings and right hand sides for
583 functions, patterns or case branches. For example, if a function @g@
589 then \tr{g} has two @Match@es: @(x,y) = y@ and @((x:ys),y) = y+1@.
591 It is always the case that each element of an @[Match]@ list has the
592 same number of @pats@s inside it. This corresponds to saying that
593 a function defined by pattern matching must have the same number of
594 patterns in each equation.
599 [LMatch id] -- The alternatives
600 PostTcType -- The type is the type of the entire group
601 -- t1 -> ... -> tn -> tr
602 -- where there are n patterns
604 type LMatch id = Located (Match id)
608 [LPat id] -- The patterns
609 (Maybe (LHsType id)) -- A type signature for the result of the match
610 -- Nothing after typechecking
613 matchGroupArity :: MatchGroup id -> Arity
614 matchGroupArity (MatchGroup [] _)
615 = panic "matchGroupArity" -- MatchGroup is never empty
616 matchGroupArity (MatchGroup (match:matches) _)
617 = ASSERT( all ((== n_pats) . length . hsLMatchPats) matches )
618 -- Assertion just checks that all the matches have the same number of pats
621 n_pats = length (hsLMatchPats match)
623 hsLMatchPats :: LMatch id -> [LPat id]
624 hsLMatchPats (L _ (Match pats _ _)) = pats
626 -- GRHSs are used both for pattern bindings and for Matches
628 = GRHSs [LGRHS id] -- Guarded RHSs
629 (HsLocalBinds id) -- The where clause
631 type LGRHS id = Located (GRHS id)
633 data GRHS id = GRHS [LStmt id] -- Guards
634 (LHsExpr id) -- Right hand side
637 We know the list must have at least one @Match@ in it.
640 pprMatches :: (OutputableBndr id) => HsMatchContext id -> MatchGroup id -> SDoc
641 pprMatches ctxt (MatchGroup matches ty) = vcat (map (pprMatch ctxt) (map unLoc matches))
642 -- Don't print the type; it's only
643 -- a place-holder before typechecking
645 -- Exported to HsBinds, which can't see the defn of HsMatchContext
646 pprFunBind :: (OutputableBndr id) => id -> MatchGroup id -> SDoc
647 pprFunBind fun matches = pprMatches (FunRhs fun) matches
649 -- Exported to HsBinds, which can't see the defn of HsMatchContext
650 pprPatBind :: (OutputableBndr bndr, OutputableBndr id)
651 => LPat bndr -> GRHSs id -> SDoc
652 pprPatBind pat grhss = sep [ppr pat, nest 4 (pprGRHSs PatBindRhs grhss)]
655 pprMatch :: OutputableBndr id => HsMatchContext id -> Match id -> SDoc
656 pprMatch ctxt (Match pats maybe_ty grhss)
657 = pp_name ctxt <+> sep [sep (map ppr pats),
659 nest 2 (pprGRHSs ctxt grhss)]
661 pp_name (FunRhs fun) = ppr fun -- Not pprBndr; the AbsBinds will
662 -- have printed the signature
663 pp_name LambdaExpr = char '\\'
664 pp_name other = empty
666 ppr_maybe_ty = case maybe_ty of
667 Just ty -> dcolon <+> ppr ty
671 pprGRHSs :: OutputableBndr id => HsMatchContext id -> GRHSs id -> SDoc
672 pprGRHSs ctxt (GRHSs grhss binds)
674 (vcat (map (pprGRHS ctxt . unLoc) grhss)
676 if isEmptyLocalBinds binds then empty
677 else text "where" $$ nest 4 (pprBinds binds))
679 pprGRHS :: OutputableBndr id => HsMatchContext id -> GRHS id -> SDoc
681 pprGRHS ctxt (GRHS [] expr)
684 pprGRHS ctxt (GRHS guards expr)
685 = sep [char '|' <+> interpp'SP guards, pp_rhs ctxt expr]
687 pp_rhs ctxt rhs = matchSeparator ctxt <+> pprDeeper (ppr rhs)
690 %************************************************************************
692 \subsection{Do stmts and list comprehensions}
694 %************************************************************************
697 type LStmt id = Located (Stmt id)
699 -- The SyntaxExprs in here are used *only* for do-notation, which
700 -- has rebindable syntax. Otherwise they are unused.
704 (SyntaxExpr id) -- The (>>=) operator
705 (SyntaxExpr id) -- The fail operator
706 -- The fail operator is noSyntaxExpr
707 -- if the pattern match can't fail
709 | ExprStmt (LHsExpr id)
710 (SyntaxExpr id) -- The (>>) operator
711 PostTcType -- Element type of the RHS (used for arrows)
713 | LetStmt (HsLocalBinds id)
715 -- ParStmts only occur in a list comprehension
716 | ParStmt [([LStmt id], [id])] -- After renaming, the ids are the binders
717 -- bound by the stmts and used subsequently
719 -- Recursive statement (see Note [RecStmt] below)
721 --- The next two fields are only valid after renaming
722 [id] -- The ids are a subset of the variables bound by the stmts
723 -- that are used in stmts that follow the RecStmt
725 [id] -- Ditto, but these variables are the "recursive" ones, that
726 -- are used before they are bound in the stmts of the RecStmt
727 -- From a type-checking point of view, these ones have to be monomorphic
729 --- These fields are only valid after typechecking
730 [PostTcExpr] -- These expressions correspond
731 -- 1-to-1 with the "recursive" [id], and are the expresions that
732 -- should be returned by the recursion. They may not quite be the
733 -- Ids themselves, because the Id may be *polymorphic*, but
734 -- the returned thing has to be *monomorphic*.
735 (DictBinds id) -- Method bindings of Ids bound by the RecStmt,
736 -- and used afterwards
739 ExprStmts are a bit tricky, because what they mean
740 depends on the context. Consider the following contexts:
742 A do expression of type (m res_ty)
743 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
744 * ExprStmt E any_ty: do { ....; E; ... }
746 Translation: E >> ...
748 A list comprehensions of type [elt_ty]
749 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
750 * ExprStmt E Bool: [ .. | .... E ]
752 [ .. | .... | ..., E | ... ]
754 Translation: if E then fail else ...
756 A guard list, guarding a RHS of type rhs_ty
757 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
758 * ExprStmt E Bool: f x | ..., E, ... = ...rhs...
760 Translation: if E then fail else ...
762 Array comprehensions are handled like list comprehensions -=chak
769 , RecStmt [a::forall a. a -> a, b]
771 [ BindStmt b (return x)
777 Here, the RecStmt binds a,b,c; but
778 - Only a,b are used in the stmts *following* the RecStmt,
779 This 'a' is *polymorphic'
780 - Only a,c are used in the stmts *inside* the RecStmt
781 *before* their bindings
782 This 'a' is monomorphic
784 Nota Bene: the two a's have different types, even though they
789 instance OutputableBndr id => Outputable (Stmt id) where
790 ppr stmt = pprStmt stmt
792 pprStmt (BindStmt pat expr _ _) = hsep [ppr pat, ptext SLIT("<-"), ppr expr]
793 pprStmt (LetStmt binds) = hsep [ptext SLIT("let"), pprBinds binds]
794 pprStmt (ExprStmt expr _ _) = ppr expr
795 pprStmt (ParStmt stmtss) = hsep (map (\stmts -> ptext SLIT("| ") <> ppr stmts) stmtss)
796 pprStmt (RecStmt segment _ _ _ _) = ptext SLIT("rec") <+> braces (vcat (map ppr segment))
798 pprDo :: OutputableBndr id => HsStmtContext any -> [LStmt id] -> LHsExpr id -> SDoc
799 pprDo DoExpr stmts body = ptext SLIT("do") <+> pprDeeperList vcat (map ppr stmts ++ [ppr body])
800 pprDo (MDoExpr _) stmts body = ptext SLIT("mdo") <+> pprDeeperList vcat (map ppr stmts ++ [ppr body])
801 pprDo ListComp stmts body = pprComp brackets stmts body
802 pprDo PArrComp stmts body = pprComp pa_brackets stmts body
803 pprDo other stmts body = panic "pprDo" -- PatGuard, ParStmtCxt
805 pprComp :: OutputableBndr id => (SDoc -> SDoc) -> [LStmt id] -> LHsExpr id -> SDoc
806 pprComp brack quals body
808 hang (ppr body <+> char '|')
812 %************************************************************************
814 Template Haskell quotation brackets
816 %************************************************************************
819 data HsSplice id = HsSplice -- $z or $(f 4)
820 id -- The id is just a unique name to
821 (LHsExpr id) -- identify this splice point
823 instance OutputableBndr id => Outputable (HsSplice id) where
826 pprSplice :: OutputableBndr id => HsSplice id -> SDoc
827 pprSplice (HsSplice n e) = char '$' <> brackets (ppr n) <> pprParendExpr e
830 data HsBracket id = ExpBr (LHsExpr id) -- [| expr |]
831 | PatBr (LPat id) -- [p| pat |]
832 | DecBr (HsGroup id) -- [d| decls |]
833 | TypBr (LHsType id) -- [t| type |]
834 | VarBr id -- 'x, ''T
836 instance OutputableBndr id => Outputable (HsBracket id) where
840 pprHsBracket (ExpBr e) = thBrackets empty (ppr e)
841 pprHsBracket (PatBr p) = thBrackets (char 'p') (ppr p)
842 pprHsBracket (DecBr d) = thBrackets (char 'd') (ppr d)
843 pprHsBracket (TypBr t) = thBrackets (char 't') (ppr t)
844 pprHsBracket (VarBr n) = char '\'' <> ppr n
845 -- Infelicity: can't show ' vs '', because
846 -- we can't ask n what its OccName is, because the
847 -- pretty-printer for HsExpr doesn't ask for NamedThings
848 -- But the pretty-printer for names will show the OccName class
850 thBrackets pp_kind pp_body = char '[' <> pp_kind <> char '|' <+>
851 pp_body <+> ptext SLIT("|]")
854 %************************************************************************
856 \subsection{Enumerations and list comprehensions}
858 %************************************************************************
863 | FromThen (LHsExpr id)
865 | FromTo (LHsExpr id)
867 | FromThenTo (LHsExpr id)
873 instance OutputableBndr id => Outputable (ArithSeqInfo id) where
874 ppr (From e1) = hcat [ppr e1, pp_dotdot]
875 ppr (FromThen e1 e2) = hcat [ppr e1, comma, space, ppr e2, pp_dotdot]
876 ppr (FromTo e1 e3) = hcat [ppr e1, pp_dotdot, ppr e3]
877 ppr (FromThenTo e1 e2 e3)
878 = hcat [ppr e1, comma, space, ppr e2, pp_dotdot, ppr e3]
880 pp_dotdot = ptext SLIT(" .. ")
884 %************************************************************************
886 \subsection{HsMatchCtxt}
888 %************************************************************************
891 data HsMatchContext id -- Context of a Match
892 = FunRhs id -- Function binding for f
893 | CaseAlt -- Guard on a case alternative
894 | LambdaExpr -- Pattern of a lambda
895 | ProcExpr -- Pattern of a proc
896 | PatBindRhs -- Pattern binding
897 | RecUpd -- Record update [used only in DsExpr to tell matchWrapper
898 -- what sort of runtime error message to generate]
899 | StmtCtxt (HsStmtContext id) -- Pattern of a do-stmt or list comprehension
902 data HsStmtContext id
905 | MDoExpr PostTcTable -- Recursive do-expression
906 -- (tiresomely, it needs table
907 -- of its return/bind ops)
908 | PArrComp -- Parallel array comprehension
909 | PatGuard (HsMatchContext id) -- Pattern guard for specified thing
910 | ParStmtCtxt (HsStmtContext id) -- A branch of a parallel stmt
914 isDoExpr :: HsStmtContext id -> Bool
915 isDoExpr DoExpr = True
916 isDoExpr (MDoExpr _) = True
917 isDoExpr other = False
921 matchSeparator (FunRhs _) = ptext SLIT("=")
922 matchSeparator CaseAlt = ptext SLIT("->")
923 matchSeparator LambdaExpr = ptext SLIT("->")
924 matchSeparator ProcExpr = ptext SLIT("->")
925 matchSeparator PatBindRhs = ptext SLIT("=")
926 matchSeparator (StmtCtxt _) = ptext SLIT("<-")
927 matchSeparator RecUpd = panic "unused"
931 pprMatchContext (FunRhs fun) = ptext SLIT("the definition of") <+> quotes (ppr fun)
932 pprMatchContext CaseAlt = ptext SLIT("a case alternative")
933 pprMatchContext RecUpd = ptext SLIT("a record-update construct")
934 pprMatchContext PatBindRhs = ptext SLIT("a pattern binding")
935 pprMatchContext LambdaExpr = ptext SLIT("a lambda abstraction")
936 pprMatchContext ProcExpr = ptext SLIT("an arrow abstraction")
937 pprMatchContext (StmtCtxt ctxt) = ptext SLIT("a pattern binding in") $$ pprStmtContext ctxt
939 pprStmtContext (ParStmtCtxt c) = sep [ptext SLIT("a parallel branch of"), pprStmtContext c]
940 pprStmtContext (PatGuard ctxt) = ptext SLIT("a pattern guard for") $$ pprMatchContext ctxt
941 pprStmtContext DoExpr = ptext SLIT("a 'do' expression")
942 pprStmtContext (MDoExpr _) = ptext SLIT("an 'mdo' expression")
943 pprStmtContext ListComp = ptext SLIT("a list comprehension")
944 pprStmtContext PArrComp = ptext SLIT("an array comprehension")
947 pprMatchRhsContext (FunRhs fun) = ptext SLIT("a right-hand side of function") <+> quotes (ppr fun)
948 pprMatchRhsContext CaseAlt = ptext SLIT("the body of a case alternative")
949 pprMatchRhsContext PatBindRhs = ptext SLIT("the right-hand side of a pattern binding")
950 pprMatchRhsContext LambdaExpr = ptext SLIT("the body of a lambda")
951 pprMatchRhsContext ProcExpr = ptext SLIT("the body of a proc")
952 pprMatchRhsContext other = panic "pprMatchRhsContext" -- RecUpd, StmtCtxt
954 -- Used for the result statement of comprehension
955 -- e.g. the 'e' in [ e | ... ]
956 -- or the 'r' in f x = r
957 pprStmtResultContext (PatGuard ctxt) = pprMatchRhsContext ctxt
958 pprStmtResultContext other = ptext SLIT("the result of") <+> pprStmtContext other
961 -- Used to generate the string for a *runtime* error message
962 matchContextErrString (FunRhs fun) = "function " ++ showSDoc (ppr fun)
963 matchContextErrString CaseAlt = "case"
964 matchContextErrString PatBindRhs = "pattern binding"
965 matchContextErrString RecUpd = "record update"
966 matchContextErrString LambdaExpr = "lambda"
967 matchContextErrString ProcExpr = "proc"
968 matchContextErrString (StmtCtxt (ParStmtCtxt c)) = matchContextErrString (StmtCtxt c)
969 matchContextErrString (StmtCtxt (PatGuard _)) = "pattern guard"
970 matchContextErrString (StmtCtxt DoExpr) = "'do' expression"
971 matchContextErrString (StmtCtxt (MDoExpr _)) = "'mdo' expression"
972 matchContextErrString (StmtCtxt ListComp) = "list comprehension"
973 matchContextErrString (StmtCtxt PArrComp) = "array comprehension"