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
189 | HsBracket (HsBracket id)
191 | HsBracketOut (HsBracket Name) -- Output of the type checker is the *original*
192 [PendingSplice] -- renamed expression, plus *typechecked* splices
193 -- to be pasted back in by the desugarer
195 | HsSpliceE (HsSplice id)
197 -----------------------------------------------------------
198 -- Arrow notation extension
200 | HsProc (LPat id) -- arrow abstraction, proc
201 (LHsCmdTop id) -- body of the abstraction
202 -- always has an empty stack
204 ---------------------------------------
205 -- The following are commands, not expressions proper
207 | HsArrApp -- Arrow tail, or arrow application (f -< arg)
208 (LHsExpr id) -- arrow expression, f
209 (LHsExpr id) -- input expression, arg
210 PostTcType -- type of the arrow expressions f,
211 -- of the form a t t', where arg :: t
212 HsArrAppType -- higher-order (-<<) or first-order (-<)
213 Bool -- True => right-to-left (f -< arg)
214 -- False => left-to-right (arg >- f)
216 | HsArrForm -- Command formation, (| e cmd1 .. cmdn |)
217 (LHsExpr id) -- the operator
218 -- after type-checking, a type abstraction to be
219 -- applied to the type of the local environment tuple
220 (Maybe Fixity) -- fixity (filled in by the renamer), for forms that
221 -- were converted from OpApp's by the renamer
222 [LHsCmdTop id] -- argument commands
226 These constructors only appear temporarily in the parser.
227 The renamer translates them into the Right Thing.
230 | EWildPat -- wildcard
232 | EAsPat (Located id) -- as pattern
235 | ELazyPat (LHsExpr id) -- ~ pattern
237 | HsType (LHsType id) -- Explicit type argument; e.g f {| Int |} x y
240 Everything from here on appears only in typechecker output.
243 | HsWrap HsWrapper -- TRANSLATION
246 type PendingSplice = (Name, LHsExpr Id) -- Typechecked splices, waiting to be
247 -- pasted back in by the desugarer
250 A @Dictionary@, unless of length 0 or 1, becomes a tuple. A
251 @ClassDictLam dictvars methods expr@ is, therefore:
253 \ x -> case x of ( dictvars-and-methods-tuple ) -> expr
257 instance OutputableBndr id => Outputable (HsExpr id) where
258 ppr expr = pprExpr expr
262 pprExpr :: OutputableBndr id => HsExpr id -> SDoc
264 pprExpr e = pprDeeper (ppr_expr e)
266 pprBinds :: OutputableBndr id => HsLocalBinds id -> SDoc
267 pprBinds b = pprDeeper (ppr b)
269 ppr_lexpr :: OutputableBndr id => LHsExpr id -> SDoc
270 ppr_lexpr e = ppr_expr (unLoc e)
272 ppr_expr (HsVar v) = pprHsVar v
273 ppr_expr (HsIPVar v) = ppr v
274 ppr_expr (HsLit lit) = ppr lit
275 ppr_expr (HsOverLit lit) = ppr lit
276 ppr_expr (HsPar e) = parens (ppr_lexpr e)
278 ppr_expr (HsCoreAnn s e)
279 = vcat [ptext SLIT("HsCoreAnn") <+> ftext s, ppr_lexpr e]
281 ppr_expr (HsApp e1 e2)
282 = let (fun, args) = collect_args e1 [e2] in
283 hang (ppr_lexpr fun) 2 (sep (map pprParendExpr args))
285 collect_args (L _ (HsApp fun arg)) args = collect_args fun (arg:args)
286 collect_args fun args = (fun, args)
288 ppr_expr (OpApp e1 op fixity e2)
290 HsVar v -> pp_infixly v
293 pp_e1 = pprParendExpr e1 -- Add parens to make precedence clear
294 pp_e2 = pprParendExpr e2
297 = hang (ppr op) 2 (sep [pp_e1, pp_e2])
300 = sep [nest 2 pp_e1, pprInfix v, nest 2 pp_e2]
302 ppr_expr (NegApp e _) = char '-' <+> pprParendExpr e
304 ppr_expr (SectionL expr op)
306 HsVar v -> pp_infixly v
309 pp_expr = pprParendExpr expr
311 pp_prefixly = hang (hsep [text " \\ x_ ->", ppr op])
312 4 (hsep [pp_expr, ptext SLIT("x_ )")])
313 pp_infixly v = parens (sep [pp_expr, pprInfix v])
315 ppr_expr (SectionR op expr)
317 HsVar v -> pp_infixly v
320 pp_expr = pprParendExpr expr
322 pp_prefixly = hang (hsep [text "( \\ x_ ->", ppr op, ptext SLIT("x_")])
323 4 ((<>) pp_expr rparen)
325 = parens (sep [pprInfix v, pp_expr])
327 ppr_expr (HsLam matches)
328 = pprMatches LambdaExpr matches
330 ppr_expr (HsCase expr matches)
331 = sep [ sep [ptext SLIT("case"), nest 4 (ppr expr), ptext SLIT("of")],
332 nest 2 (pprMatches CaseAlt matches) ]
334 ppr_expr (HsIf e1 e2 e3)
335 = sep [hsep [ptext SLIT("if"), nest 2 (ppr e1), ptext SLIT("then")],
340 -- special case: let ... in let ...
341 ppr_expr (HsLet binds expr@(L _ (HsLet _ _)))
342 = sep [hang (ptext SLIT("let")) 2 (hsep [pprBinds binds, ptext SLIT("in")]),
345 ppr_expr (HsLet binds expr)
346 = sep [hang (ptext SLIT("let")) 2 (pprBinds binds),
347 hang (ptext SLIT("in")) 2 (ppr expr)]
349 ppr_expr (HsDo do_or_list_comp stmts body _) = pprDo do_or_list_comp stmts body
351 ppr_expr (ExplicitList _ exprs)
352 = brackets (fsep (punctuate comma (map ppr_lexpr exprs)))
354 ppr_expr (ExplicitPArr _ exprs)
355 = pa_brackets (fsep (punctuate comma (map ppr_lexpr exprs)))
357 ppr_expr (ExplicitTuple exprs boxity)
358 = tupleParens boxity (sep (punctuate comma (map ppr_lexpr exprs)))
360 ppr_expr (RecordCon con_id con_expr rbinds)
361 = pp_rbinds (ppr con_id) rbinds
363 ppr_expr (RecordUpd aexp rbinds _ _)
364 = pp_rbinds (pprParendExpr aexp) rbinds
366 ppr_expr (ExprWithTySig expr sig)
367 = hang (nest 2 (ppr_lexpr expr) <+> dcolon)
369 ppr_expr (ExprWithTySigOut expr sig)
370 = hang (nest 2 (ppr_lexpr expr) <+> dcolon)
373 ppr_expr (ArithSeq expr info) = brackets (ppr info)
374 ppr_expr (PArrSeq expr info) = pa_brackets (ppr info)
376 ppr_expr EWildPat = char '_'
377 ppr_expr (ELazyPat e) = char '~' <> pprParendExpr e
378 ppr_expr (EAsPat v e) = ppr v <> char '@' <> pprParendExpr e
380 ppr_expr (HsSCC lbl expr)
381 = sep [ ptext SLIT("_scc_") <+> doubleQuotes (ftext lbl), pprParendExpr expr ]
383 ppr_expr (HsWrap co_fn e) = pprHsWrapper (ppr_expr e) co_fn
384 ppr_expr (HsType id) = ppr id
386 ppr_expr (HsSpliceE s) = pprSplice s
387 ppr_expr (HsBracket b) = pprHsBracket b
388 ppr_expr (HsBracketOut e []) = ppr e
389 ppr_expr (HsBracketOut e ps) = ppr e $$ ptext SLIT("pending") <+> ppr ps
391 ppr_expr (HsProc pat (L _ (HsCmdTop cmd _ _ _)))
392 = hsep [ptext SLIT("proc"), ppr pat, ptext SLIT("->"), ppr cmd]
394 ppr_expr (HsArrApp arrow arg _ HsFirstOrderApp True)
395 = hsep [ppr_lexpr arrow, ptext SLIT("-<"), ppr_lexpr arg]
396 ppr_expr (HsArrApp arrow arg _ HsFirstOrderApp False)
397 = hsep [ppr_lexpr arg, ptext SLIT(">-"), ppr_lexpr arrow]
398 ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp True)
399 = hsep [ppr_lexpr arrow, ptext SLIT("-<<"), ppr_lexpr arg]
400 ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp False)
401 = hsep [ppr_lexpr arg, ptext SLIT(">>-"), ppr_lexpr arrow]
403 ppr_expr (HsArrForm (L _ (HsVar v)) (Just _) [arg1, arg2])
404 = sep [pprCmdArg (unLoc arg1), hsep [pprInfix v, pprCmdArg (unLoc arg2)]]
405 ppr_expr (HsArrForm op _ args)
406 = hang (ptext SLIT("(|") <> ppr_lexpr op)
407 4 (sep (map (pprCmdArg.unLoc) args) <> ptext SLIT("|)"))
409 pprCmdArg :: OutputableBndr id => HsCmdTop id -> SDoc
410 pprCmdArg (HsCmdTop cmd@(L _ (HsArrForm _ Nothing [])) _ _ _)
412 pprCmdArg (HsCmdTop cmd _ _ _)
413 = parens (ppr_lexpr cmd)
415 -- Put a var in backquotes if it's not an operator already
416 pprInfix :: Outputable name => name -> SDoc
417 pprInfix v | isOperator ppr_v = ppr_v
418 | otherwise = char '`' <> ppr_v <> char '`'
422 -- add parallel array brackets around a document
424 pa_brackets :: SDoc -> SDoc
425 pa_brackets p = ptext SLIT("[:") <> p <> ptext SLIT(":]")
428 Parenthesize unless very simple:
430 pprParendExpr :: OutputableBndr id => LHsExpr id -> SDoc
433 pp_as_was = ppr_lexpr expr
434 -- Using ppr_expr here avoids the call to 'deeper'
435 -- Not sure if that's always right.
442 HsIPVar _ -> pp_as_was
443 ExplicitList _ _ -> pp_as_was
444 ExplicitPArr _ _ -> pp_as_was
445 ExplicitTuple _ _ -> pp_as_was
447 HsBracket _ -> pp_as_was
448 HsBracketOut _ [] -> pp_as_was
450 _ -> parens pp_as_was
453 %************************************************************************
455 \subsection{Commands (in arrow abstractions)}
457 %************************************************************************
459 We re-use HsExpr to represent these.
462 type HsCmd id = HsExpr id
464 type LHsCmd id = LHsExpr id
466 data HsArrAppType = HsHigherOrderApp | HsFirstOrderApp
469 The legal constructors for commands are:
471 = HsArrApp ... -- as above
473 | HsArrForm ... -- as above
478 | HsLam (Match id) -- kappa
480 -- the renamer turns this one into HsArrForm
481 | OpApp (HsExpr id) -- left operand
482 (HsCmd id) -- operator
483 Fixity -- Renamer adds fixity; bottom until then
484 (HsCmd id) -- right operand
486 | HsPar (HsCmd id) -- parenthesised command
489 [Match id] -- bodies are HsCmd's
492 | HsIf (HsExpr id) -- predicate
493 (HsCmd id) -- then part
494 (HsCmd id) -- else part
497 | HsLet (HsLocalBinds id) -- let(rec)
500 | HsDo (HsStmtContext Name) -- The parameterisation is unimportant
501 -- because in this context we never use
502 -- the PatGuard or ParStmt variant
503 [Stmt id] -- HsExpr's are really HsCmd's
504 PostTcType -- Type of the whole expression
507 Top-level command, introducing a new arrow.
508 This may occur inside a proc (where the stack is empty) or as an
509 argument of a command-forming operator.
512 type LHsCmdTop id = Located (HsCmdTop id)
515 = HsCmdTop (LHsCmd id)
516 [PostTcType] -- types of inputs on the command's stack
517 PostTcType -- return type of the command
519 -- after type checking:
520 -- names used in the command's desugaring
523 %************************************************************************
525 \subsection{Record binds}
527 %************************************************************************
530 type HsRecordBinds id = [(Located id, LHsExpr id)]
532 recBindFields :: HsRecordBinds id -> [id]
533 recBindFields rbinds = [unLoc field | (field,_) <- rbinds]
535 pp_rbinds :: OutputableBndr id => SDoc -> HsRecordBinds id -> SDoc
536 pp_rbinds thing rbinds
538 4 (braces (sep (punctuate comma (map (pp_rbind) rbinds))))
540 pp_rbind (v, e) = hsep [pprBndr LetBind (unLoc v), char '=', ppr e]
545 %************************************************************************
547 \subsection{@Match@, @GRHSs@, and @GRHS@ datatypes}
549 %************************************************************************
551 @Match@es are sets of pattern bindings and right hand sides for
552 functions, patterns or case branches. For example, if a function @g@
558 then \tr{g} has two @Match@es: @(x,y) = y@ and @((x:ys),y) = y+1@.
560 It is always the case that each element of an @[Match]@ list has the
561 same number of @pats@s inside it. This corresponds to saying that
562 a function defined by pattern matching must have the same number of
563 patterns in each equation.
568 [LMatch id] -- The alternatives
569 PostTcType -- The type is the type of the entire group
570 -- t1 -> ... -> tn -> tr
571 -- where there are n patterns
573 type LMatch id = Located (Match id)
577 [LPat id] -- The patterns
578 (Maybe (LHsType id)) -- A type signature for the result of the match
579 -- Nothing after typechecking
582 matchGroupArity :: MatchGroup id -> Arity
583 matchGroupArity (MatchGroup [] _)
584 = panic "matchGroupArity" -- MatchGroup is never empty
585 matchGroupArity (MatchGroup (match:matches) _)
586 = ASSERT( all ((== n_pats) . length . hsLMatchPats) matches )
587 -- Assertion just checks that all the matches have the same number of pats
590 n_pats = length (hsLMatchPats match)
592 hsLMatchPats :: LMatch id -> [LPat id]
593 hsLMatchPats (L _ (Match pats _ _)) = pats
595 -- GRHSs are used both for pattern bindings and for Matches
597 = GRHSs [LGRHS id] -- Guarded RHSs
598 (HsLocalBinds id) -- The where clause
600 type LGRHS id = Located (GRHS id)
602 data GRHS id = GRHS [LStmt id] -- Guards
603 (LHsExpr id) -- Right hand side
606 We know the list must have at least one @Match@ in it.
609 pprMatches :: (OutputableBndr id) => HsMatchContext id -> MatchGroup id -> SDoc
610 pprMatches ctxt (MatchGroup matches ty) = vcat (map (pprMatch ctxt) (map unLoc matches))
611 -- Don't print the type; it's only
612 -- a place-holder before typechecking
614 -- Exported to HsBinds, which can't see the defn of HsMatchContext
615 pprFunBind :: (OutputableBndr id) => id -> MatchGroup id -> SDoc
616 pprFunBind fun matches = pprMatches (FunRhs fun) matches
618 -- Exported to HsBinds, which can't see the defn of HsMatchContext
619 pprPatBind :: (OutputableBndr bndr, OutputableBndr id)
620 => LPat bndr -> GRHSs id -> SDoc
621 pprPatBind pat grhss = sep [ppr pat, nest 4 (pprGRHSs PatBindRhs grhss)]
624 pprMatch :: OutputableBndr id => HsMatchContext id -> Match id -> SDoc
625 pprMatch ctxt (Match pats maybe_ty grhss)
626 = pp_name ctxt <+> sep [sep (map ppr pats),
628 nest 2 (pprGRHSs ctxt grhss)]
630 pp_name (FunRhs fun) = ppr fun -- Not pprBndr; the AbsBinds will
631 -- have printed the signature
632 pp_name LambdaExpr = char '\\'
633 pp_name other = empty
635 ppr_maybe_ty = case maybe_ty of
636 Just ty -> dcolon <+> ppr ty
640 pprGRHSs :: OutputableBndr id => HsMatchContext id -> GRHSs id -> SDoc
641 pprGRHSs ctxt (GRHSs grhss binds)
642 = vcat (map (pprGRHS ctxt . unLoc) grhss)
644 (if isEmptyLocalBinds binds then empty
645 else text "where" $$ nest 4 (pprBinds binds))
647 pprGRHS :: OutputableBndr id => HsMatchContext id -> GRHS id -> SDoc
649 pprGRHS ctxt (GRHS [] expr)
652 pprGRHS ctxt (GRHS guards expr)
653 = sep [char '|' <+> interpp'SP guards, pp_rhs ctxt expr]
655 pp_rhs ctxt rhs = matchSeparator ctxt <+> pprDeeper (ppr rhs)
658 %************************************************************************
660 \subsection{Do stmts and list comprehensions}
662 %************************************************************************
665 type LStmt id = Located (Stmt id)
667 -- The SyntaxExprs in here are used *only* for do-notation, which
668 -- has rebindable syntax. Otherwise they are unused.
672 (SyntaxExpr id) -- The (>>=) operator
673 (SyntaxExpr id) -- The fail operator
674 -- The fail operator is noSyntaxExpr
675 -- if the pattern match can't fail
677 | ExprStmt (LHsExpr id)
678 (SyntaxExpr id) -- The (>>) operator
679 PostTcType -- Element type of the RHS (used for arrows)
681 | LetStmt (HsLocalBinds id)
683 -- ParStmts only occur in a list comprehension
684 | ParStmt [([LStmt id], [id])] -- After renaming, the ids are the binders
685 -- bound by the stmts and used subsequently
687 -- Recursive statement (see Note [RecStmt] below)
689 --- The next two fields are only valid after renaming
690 [id] -- The ids are a subset of the variables bound by the stmts
691 -- that are used in stmts that follow the RecStmt
693 [id] -- Ditto, but these variables are the "recursive" ones, that
694 -- are used before they are bound in the stmts of the RecStmt
695 -- From a type-checking point of view, these ones have to be monomorphic
697 --- These fields are only valid after typechecking
698 [PostTcExpr] -- These expressions correspond
699 -- 1-to-1 with the "recursive" [id], and are the expresions that
700 -- should be returned by the recursion. They may not quite be the
701 -- Ids themselves, because the Id may be *polymorphic*, but
702 -- the returned thing has to be *monomorphic*.
703 (DictBinds id) -- Method bindings of Ids bound by the RecStmt,
704 -- and used afterwards
707 ExprStmts are a bit tricky, because what they mean
708 depends on the context. Consider the following contexts:
710 A do expression of type (m res_ty)
711 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
712 * ExprStmt E any_ty: do { ....; E; ... }
714 Translation: E >> ...
716 A list comprehensions of type [elt_ty]
717 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
718 * ExprStmt E Bool: [ .. | .... E ]
720 [ .. | .... | ..., E | ... ]
722 Translation: if E then fail else ...
724 A guard list, guarding a RHS of type rhs_ty
725 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
726 * ExprStmt E Bool: f x | ..., E, ... = ...rhs...
728 Translation: if E then fail else ...
730 Array comprehensions are handled like list comprehensions -=chak
737 , RecStmt [a::forall a. a -> a, b]
739 [ BindStmt b (return x)
745 Here, the RecStmt binds a,b,c; but
746 - Only a,b are used in the stmts *following* the RecStmt,
747 This 'a' is *polymorphic'
748 - Only a,c are used in the stmts *inside* the RecStmt
749 *before* their bindings
750 This 'a' is monomorphic
752 Nota Bene: the two a's have different types, even though they
757 instance OutputableBndr id => Outputable (Stmt id) where
758 ppr stmt = pprStmt stmt
760 pprStmt (BindStmt pat expr _ _) = hsep [ppr pat, ptext SLIT("<-"), ppr expr]
761 pprStmt (LetStmt binds) = hsep [ptext SLIT("let"), pprBinds binds]
762 pprStmt (ExprStmt expr _ _) = ppr expr
763 pprStmt (ParStmt stmtss) = hsep (map (\stmts -> ptext SLIT("| ") <> ppr stmts) stmtss)
764 pprStmt (RecStmt segment _ _ _ _) = ptext SLIT("rec") <+> braces (vcat (map ppr segment))
766 pprDo :: OutputableBndr id => HsStmtContext any -> [LStmt id] -> LHsExpr id -> SDoc
767 pprDo DoExpr stmts body = ptext SLIT("do") <+> (vcat (map ppr stmts) $$ ppr body)
768 pprDo (MDoExpr _) stmts body = ptext SLIT("mdo") <+> (vcat (map ppr stmts) $$ ppr body)
769 pprDo ListComp stmts body = pprComp brackets stmts body
770 pprDo PArrComp stmts body = pprComp pa_brackets stmts body
771 pprDo other stmts body = panic "pprDo" -- PatGuard, ParStmtCxt
773 pprComp :: OutputableBndr id => (SDoc -> SDoc) -> [LStmt id] -> LHsExpr id -> SDoc
774 pprComp brack quals body
776 hang (ppr body <+> char '|')
780 %************************************************************************
782 Template Haskell quotation brackets
784 %************************************************************************
787 data HsSplice id = HsSplice -- $z or $(f 4)
788 id -- The id is just a unique name to
789 (LHsExpr id) -- identify this splice point
791 instance OutputableBndr id => Outputable (HsSplice id) where
794 pprSplice :: OutputableBndr id => HsSplice id -> SDoc
795 pprSplice (HsSplice n e) = char '$' <> brackets (ppr n) <> pprParendExpr e
798 data HsBracket id = ExpBr (LHsExpr id) -- [| expr |]
799 | PatBr (LPat id) -- [p| pat |]
800 | DecBr (HsGroup id) -- [d| decls |]
801 | TypBr (LHsType id) -- [t| type |]
802 | VarBr id -- 'x, ''T
804 instance OutputableBndr id => Outputable (HsBracket id) where
808 pprHsBracket (ExpBr e) = thBrackets empty (ppr e)
809 pprHsBracket (PatBr p) = thBrackets (char 'p') (ppr p)
810 pprHsBracket (DecBr d) = thBrackets (char 'd') (ppr d)
811 pprHsBracket (TypBr t) = thBrackets (char 't') (ppr t)
812 pprHsBracket (VarBr n) = char '\'' <> ppr n
813 -- Infelicity: can't show ' vs '', because
814 -- we can't ask n what its OccName is, because the
815 -- pretty-printer for HsExpr doesn't ask for NamedThings
816 -- But the pretty-printer for names will show the OccName class
818 thBrackets pp_kind pp_body = char '[' <> pp_kind <> char '|' <+>
819 pp_body <+> ptext SLIT("|]")
822 %************************************************************************
824 \subsection{Enumerations and list comprehensions}
826 %************************************************************************
831 | FromThen (LHsExpr id)
833 | FromTo (LHsExpr id)
835 | FromThenTo (LHsExpr id)
841 instance OutputableBndr id => Outputable (ArithSeqInfo id) where
842 ppr (From e1) = hcat [ppr e1, pp_dotdot]
843 ppr (FromThen e1 e2) = hcat [ppr e1, comma, space, ppr e2, pp_dotdot]
844 ppr (FromTo e1 e3) = hcat [ppr e1, pp_dotdot, ppr e3]
845 ppr (FromThenTo e1 e2 e3)
846 = hcat [ppr e1, comma, space, ppr e2, pp_dotdot, ppr e3]
848 pp_dotdot = ptext SLIT(" .. ")
852 %************************************************************************
854 \subsection{HsMatchCtxt}
856 %************************************************************************
859 data HsMatchContext id -- Context of a Match
860 = FunRhs id -- Function binding for f
861 | CaseAlt -- Guard on a case alternative
862 | LambdaExpr -- Pattern of a lambda
863 | ProcExpr -- Pattern of a proc
864 | PatBindRhs -- Pattern binding
865 | RecUpd -- Record update [used only in DsExpr to tell matchWrapper
866 -- what sort of runtime error message to generate]
867 | StmtCtxt (HsStmtContext id) -- Pattern of a do-stmt or list comprehension
870 data HsStmtContext id
873 | MDoExpr PostTcTable -- Recursive do-expression
874 -- (tiresomely, it needs table
875 -- of its return/bind ops)
876 | PArrComp -- Parallel array comprehension
877 | PatGuard (HsMatchContext id) -- Pattern guard for specified thing
878 | ParStmtCtxt (HsStmtContext id) -- A branch of a parallel stmt
882 isDoExpr :: HsStmtContext id -> Bool
883 isDoExpr DoExpr = True
884 isDoExpr (MDoExpr _) = True
885 isDoExpr other = False
889 matchSeparator (FunRhs _) = ptext SLIT("=")
890 matchSeparator CaseAlt = ptext SLIT("->")
891 matchSeparator LambdaExpr = ptext SLIT("->")
892 matchSeparator ProcExpr = ptext SLIT("->")
893 matchSeparator PatBindRhs = ptext SLIT("=")
894 matchSeparator (StmtCtxt _) = ptext SLIT("<-")
895 matchSeparator RecUpd = panic "unused"
899 pprMatchContext (FunRhs fun) = ptext SLIT("the definition of") <+> quotes (ppr fun)
900 pprMatchContext CaseAlt = ptext SLIT("a case alternative")
901 pprMatchContext RecUpd = ptext SLIT("a record-update construct")
902 pprMatchContext PatBindRhs = ptext SLIT("a pattern binding")
903 pprMatchContext LambdaExpr = ptext SLIT("a lambda abstraction")
904 pprMatchContext ProcExpr = ptext SLIT("an arrow abstraction")
905 pprMatchContext (StmtCtxt ctxt) = ptext SLIT("a pattern binding in") $$ pprStmtContext ctxt
907 pprStmtContext (ParStmtCtxt c) = sep [ptext SLIT("a parallel branch of"), pprStmtContext c]
908 pprStmtContext (PatGuard ctxt) = ptext SLIT("a pattern guard for") $$ pprMatchContext ctxt
909 pprStmtContext DoExpr = ptext SLIT("a 'do' expression")
910 pprStmtContext (MDoExpr _) = ptext SLIT("an 'mdo' expression")
911 pprStmtContext ListComp = ptext SLIT("a list comprehension")
912 pprStmtContext PArrComp = ptext SLIT("an array comprehension")
915 pprMatchRhsContext (FunRhs fun) = ptext SLIT("a right-hand side of function") <+> quotes (ppr fun)
916 pprMatchRhsContext CaseAlt = ptext SLIT("the body of a case alternative")
917 pprMatchRhsContext PatBindRhs = ptext SLIT("the right-hand side of a pattern binding")
918 pprMatchRhsContext LambdaExpr = ptext SLIT("the body of a lambda")
919 pprMatchRhsContext ProcExpr = ptext SLIT("the body of a proc")
920 pprMatchRhsContext other = panic "pprMatchRhsContext" -- RecUpd, StmtCtxt
922 -- Used for the result statement of comprehension
923 -- e.g. the 'e' in [ e | ... ]
924 -- or the 'r' in f x = r
925 pprStmtResultContext (PatGuard ctxt) = pprMatchRhsContext ctxt
926 pprStmtResultContext other = ptext SLIT("the result of") <+> pprStmtContext other
929 -- Used to generate the string for a *runtime* error message
930 matchContextErrString (FunRhs fun) = "function " ++ showSDoc (ppr fun)
931 matchContextErrString CaseAlt = "case"
932 matchContextErrString PatBindRhs = "pattern binding"
933 matchContextErrString RecUpd = "record update"
934 matchContextErrString LambdaExpr = "lambda"
935 matchContextErrString ProcExpr = "proc"
936 matchContextErrString (StmtCtxt (ParStmtCtxt c)) = matchContextErrString (StmtCtxt c)
937 matchContextErrString (StmtCtxt (PatGuard _)) = "pattern guard"
938 matchContextErrString (StmtCtxt DoExpr) = "'do' expression"
939 matchContextErrString (StmtCtxt (MDoExpr _)) = "'mdo' expression"
940 matchContextErrString (StmtCtxt ListComp) = "list comprehension"
941 matchContextErrString (StmtCtxt PArrComp) = "array comprehension"