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 ---------------------------------------
208 Int -- module-local tick number
209 (LHsExpr id) -- sub-expression
212 Int -- module-local tick number for True
213 Int -- module-local tick number for False
214 (LHsExpr id) -- sub-expression
216 ---------------------------------------
217 -- The following are commands, not expressions proper
219 | HsArrApp -- Arrow tail, or arrow application (f -< arg)
220 (LHsExpr id) -- arrow expression, f
221 (LHsExpr id) -- input expression, arg
222 PostTcType -- type of the arrow expressions f,
223 -- of the form a t t', where arg :: t
224 HsArrAppType -- higher-order (-<<) or first-order (-<)
225 Bool -- True => right-to-left (f -< arg)
226 -- False => left-to-right (arg >- f)
228 | HsArrForm -- Command formation, (| e cmd1 .. cmdn |)
229 (LHsExpr id) -- the operator
230 -- after type-checking, a type abstraction to be
231 -- applied to the type of the local environment tuple
232 (Maybe Fixity) -- fixity (filled in by the renamer), for forms that
233 -- were converted from OpApp's by the renamer
234 [LHsCmdTop id] -- argument commands
238 These constructors only appear temporarily in the parser.
239 The renamer translates them into the Right Thing.
242 | EWildPat -- wildcard
244 | EAsPat (Located id) -- as pattern
247 | ELazyPat (LHsExpr id) -- ~ pattern
249 | HsType (LHsType id) -- Explicit type argument; e.g f {| Int |} x y
252 Everything from here on appears only in typechecker output.
255 | HsWrap HsWrapper -- TRANSLATION
258 type PendingSplice = (Name, LHsExpr Id) -- Typechecked splices, waiting to be
259 -- pasted back in by the desugarer
262 A @Dictionary@, unless of length 0 or 1, becomes a tuple. A
263 @ClassDictLam dictvars methods expr@ is, therefore:
265 \ x -> case x of ( dictvars-and-methods-tuple ) -> expr
269 instance OutputableBndr id => Outputable (HsExpr id) where
270 ppr expr = pprExpr expr
274 pprExpr :: OutputableBndr id => HsExpr id -> SDoc
276 pprExpr e = pprDeeper (ppr_expr e)
278 pprBinds :: OutputableBndr id => HsLocalBinds id -> SDoc
279 pprBinds b = pprDeeper (ppr b)
281 ppr_lexpr :: OutputableBndr id => LHsExpr id -> SDoc
282 ppr_lexpr e = ppr_expr (unLoc e)
284 ppr_expr (HsVar v) = pprHsVar v
285 ppr_expr (HsIPVar v) = ppr v
286 ppr_expr (HsLit lit) = ppr lit
287 ppr_expr (HsOverLit lit) = ppr lit
288 ppr_expr (HsPar e) = parens (ppr_lexpr e)
290 ppr_expr (HsCoreAnn s e)
291 = vcat [ptext SLIT("HsCoreAnn") <+> ftext s, ppr_lexpr e]
293 ppr_expr (HsApp e1 e2)
294 = let (fun, args) = collect_args e1 [e2] in
295 hang (ppr_lexpr fun) 2 (sep (map pprParendExpr args))
297 collect_args (L _ (HsApp fun arg)) args = collect_args fun (arg:args)
298 collect_args fun args = (fun, args)
300 ppr_expr (OpApp e1 op fixity e2)
302 HsVar v -> pp_infixly v
305 pp_e1 = pprParendExpr e1 -- Add parens to make precedence clear
306 pp_e2 = pprParendExpr e2
309 = hang (ppr op) 2 (sep [pp_e1, pp_e2])
312 = sep [nest 2 pp_e1, pprInfix v, nest 2 pp_e2]
314 ppr_expr (NegApp e _) = char '-' <+> pprParendExpr e
316 ppr_expr (SectionL expr op)
318 HsVar v -> pp_infixly v
321 pp_expr = pprParendExpr expr
323 pp_prefixly = hang (hsep [text " \\ x_ ->", ppr op])
324 4 (hsep [pp_expr, ptext SLIT("x_ )")])
325 pp_infixly v = parens (sep [pp_expr, pprInfix v])
327 ppr_expr (SectionR op expr)
329 HsVar v -> pp_infixly v
332 pp_expr = pprParendExpr expr
334 pp_prefixly = hang (hsep [text "( \\ x_ ->", ppr op, ptext SLIT("x_")])
335 4 ((<>) pp_expr rparen)
337 = parens (sep [pprInfix v, pp_expr])
339 ppr_expr (HsLam matches)
340 = pprMatches LambdaExpr matches
342 ppr_expr (HsCase expr matches)
343 = sep [ sep [ptext SLIT("case"), nest 4 (ppr expr), ptext SLIT("of")],
344 nest 2 (pprMatches CaseAlt matches) ]
346 ppr_expr (HsIf e1 e2 e3)
347 = sep [hsep [ptext SLIT("if"), nest 2 (ppr e1), ptext SLIT("then")],
352 -- special case: let ... in let ...
353 ppr_expr (HsLet binds expr@(L _ (HsLet _ _)))
354 = sep [hang (ptext SLIT("let")) 2 (hsep [pprBinds binds, ptext SLIT("in")]),
357 ppr_expr (HsLet binds expr)
358 = sep [hang (ptext SLIT("let")) 2 (pprBinds binds),
359 hang (ptext SLIT("in")) 2 (ppr expr)]
361 ppr_expr (HsDo do_or_list_comp stmts body _) = pprDo do_or_list_comp stmts body
363 ppr_expr (ExplicitList _ exprs)
364 = brackets (fsep (punctuate comma (map ppr_lexpr exprs)))
366 ppr_expr (ExplicitPArr _ exprs)
367 = pa_brackets (fsep (punctuate comma (map ppr_lexpr exprs)))
369 ppr_expr (ExplicitTuple exprs boxity)
370 = tupleParens boxity (sep (punctuate comma (map ppr_lexpr exprs)))
372 ppr_expr (RecordCon con_id con_expr rbinds)
373 = pp_rbinds (ppr con_id) rbinds
375 ppr_expr (RecordUpd aexp rbinds _ _)
376 = pp_rbinds (pprParendExpr aexp) rbinds
378 ppr_expr (ExprWithTySig expr sig)
379 = hang (nest 2 (ppr_lexpr expr) <+> dcolon)
381 ppr_expr (ExprWithTySigOut expr sig)
382 = hang (nest 2 (ppr_lexpr expr) <+> dcolon)
385 ppr_expr (ArithSeq expr info) = brackets (ppr info)
386 ppr_expr (PArrSeq expr info) = pa_brackets (ppr info)
388 ppr_expr EWildPat = char '_'
389 ppr_expr (ELazyPat e) = char '~' <> pprParendExpr e
390 ppr_expr (EAsPat v e) = ppr v <> char '@' <> pprParendExpr e
392 ppr_expr (HsSCC lbl expr)
393 = sep [ ptext SLIT("_scc_") <+> doubleQuotes (ftext lbl), pprParendExpr expr ]
395 ppr_expr (HsWrap co_fn e) = pprHsWrapper (ppr_expr e) co_fn
396 ppr_expr (HsType id) = ppr id
398 ppr_expr (HsSpliceE s) = pprSplice s
399 ppr_expr (HsBracket b) = pprHsBracket b
400 ppr_expr (HsBracketOut e []) = ppr e
401 ppr_expr (HsBracketOut e ps) = ppr e $$ ptext SLIT("pending") <+> ppr ps
403 ppr_expr (HsProc pat (L _ (HsCmdTop cmd _ _ _)))
404 = hsep [ptext SLIT("proc"), ppr pat, ptext SLIT("->"), ppr cmd]
406 ppr_expr (HsTick tickId exp)
407 = hcat [ptext SLIT("tick<"), ppr tickId,ptext SLIT(">("), ppr exp,ptext SLIT(")")]
408 ppr_expr (HsBinTick tickIdTrue tickIdFalse exp)
409 = hcat [ptext SLIT("bintick<"),
414 ppr exp,ptext SLIT(")")]
416 ppr_expr (HsArrApp arrow arg _ HsFirstOrderApp True)
417 = hsep [ppr_lexpr arrow, ptext SLIT("-<"), ppr_lexpr arg]
418 ppr_expr (HsArrApp arrow arg _ HsFirstOrderApp False)
419 = hsep [ppr_lexpr arg, ptext SLIT(">-"), ppr_lexpr arrow]
420 ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp True)
421 = hsep [ppr_lexpr arrow, ptext SLIT("-<<"), ppr_lexpr arg]
422 ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp False)
423 = hsep [ppr_lexpr arg, ptext SLIT(">>-"), ppr_lexpr arrow]
425 ppr_expr (HsArrForm (L _ (HsVar v)) (Just _) [arg1, arg2])
426 = sep [pprCmdArg (unLoc arg1), hsep [pprInfix v, pprCmdArg (unLoc arg2)]]
427 ppr_expr (HsArrForm op _ args)
428 = hang (ptext SLIT("(|") <> ppr_lexpr op)
429 4 (sep (map (pprCmdArg.unLoc) args) <> ptext SLIT("|)"))
431 pprCmdArg :: OutputableBndr id => HsCmdTop id -> SDoc
432 pprCmdArg (HsCmdTop cmd@(L _ (HsArrForm _ Nothing [])) _ _ _)
434 pprCmdArg (HsCmdTop cmd _ _ _)
435 = parens (ppr_lexpr cmd)
437 -- Put a var in backquotes if it's not an operator already
438 pprInfix :: Outputable name => name -> SDoc
439 pprInfix v | isOperator ppr_v = ppr_v
440 | otherwise = char '`' <> ppr_v <> char '`'
444 -- add parallel array brackets around a document
446 pa_brackets :: SDoc -> SDoc
447 pa_brackets p = ptext SLIT("[:") <> p <> ptext SLIT(":]")
450 Parenthesize unless very simple:
452 pprParendExpr :: OutputableBndr id => LHsExpr id -> SDoc
455 pp_as_was = ppr_lexpr expr
456 -- Using ppr_expr here avoids the call to 'deeper'
457 -- Not sure if that's always right.
464 HsIPVar _ -> pp_as_was
465 ExplicitList _ _ -> pp_as_was
466 ExplicitPArr _ _ -> pp_as_was
467 ExplicitTuple _ _ -> pp_as_was
469 HsBracket _ -> pp_as_was
470 HsBracketOut _ [] -> pp_as_was
472 _ -> parens pp_as_was
475 %************************************************************************
477 \subsection{Commands (in arrow abstractions)}
479 %************************************************************************
481 We re-use HsExpr to represent these.
484 type HsCmd id = HsExpr id
486 type LHsCmd id = LHsExpr id
488 data HsArrAppType = HsHigherOrderApp | HsFirstOrderApp
491 The legal constructors for commands are:
493 = HsArrApp ... -- as above
495 | HsArrForm ... -- as above
500 | HsLam (Match id) -- kappa
502 -- the renamer turns this one into HsArrForm
503 | OpApp (HsExpr id) -- left operand
504 (HsCmd id) -- operator
505 Fixity -- Renamer adds fixity; bottom until then
506 (HsCmd id) -- right operand
508 | HsPar (HsCmd id) -- parenthesised command
511 [Match id] -- bodies are HsCmd's
514 | HsIf (HsExpr id) -- predicate
515 (HsCmd id) -- then part
516 (HsCmd id) -- else part
519 | HsLet (HsLocalBinds id) -- let(rec)
522 | HsDo (HsStmtContext Name) -- The parameterisation is unimportant
523 -- because in this context we never use
524 -- the PatGuard or ParStmt variant
525 [Stmt id] -- HsExpr's are really HsCmd's
526 PostTcType -- Type of the whole expression
529 Top-level command, introducing a new arrow.
530 This may occur inside a proc (where the stack is empty) or as an
531 argument of a command-forming operator.
534 type LHsCmdTop id = Located (HsCmdTop id)
537 = HsCmdTop (LHsCmd id)
538 [PostTcType] -- types of inputs on the command's stack
539 PostTcType -- return type of the command
541 -- after type checking:
542 -- names used in the command's desugaring
545 %************************************************************************
547 \subsection{Record binds}
549 %************************************************************************
552 type HsRecordBinds id = [(Located id, LHsExpr id)]
554 recBindFields :: HsRecordBinds id -> [id]
555 recBindFields rbinds = [unLoc field | (field,_) <- rbinds]
557 pp_rbinds :: OutputableBndr id => SDoc -> HsRecordBinds id -> SDoc
558 pp_rbinds thing rbinds
560 4 (braces (sep (punctuate comma (map (pp_rbind) rbinds))))
562 pp_rbind (v, e) = hsep [pprBndr LetBind (unLoc v), char '=', ppr e]
567 %************************************************************************
569 \subsection{@Match@, @GRHSs@, and @GRHS@ datatypes}
571 %************************************************************************
573 @Match@es are sets of pattern bindings and right hand sides for
574 functions, patterns or case branches. For example, if a function @g@
580 then \tr{g} has two @Match@es: @(x,y) = y@ and @((x:ys),y) = y+1@.
582 It is always the case that each element of an @[Match]@ list has the
583 same number of @pats@s inside it. This corresponds to saying that
584 a function defined by pattern matching must have the same number of
585 patterns in each equation.
590 [LMatch id] -- The alternatives
591 PostTcType -- The type is the type of the entire group
592 -- t1 -> ... -> tn -> tr
593 -- where there are n patterns
595 type LMatch id = Located (Match id)
599 [LPat id] -- The patterns
600 (Maybe (LHsType id)) -- A type signature for the result of the match
601 -- Nothing after typechecking
604 matchGroupArity :: MatchGroup id -> Arity
605 matchGroupArity (MatchGroup [] _)
606 = panic "matchGroupArity" -- MatchGroup is never empty
607 matchGroupArity (MatchGroup (match:matches) _)
608 = ASSERT( all ((== n_pats) . length . hsLMatchPats) matches )
609 -- Assertion just checks that all the matches have the same number of pats
612 n_pats = length (hsLMatchPats match)
614 hsLMatchPats :: LMatch id -> [LPat id]
615 hsLMatchPats (L _ (Match pats _ _)) = pats
617 -- GRHSs are used both for pattern bindings and for Matches
619 = GRHSs [LGRHS id] -- Guarded RHSs
620 (HsLocalBinds id) -- The where clause
622 type LGRHS id = Located (GRHS id)
624 data GRHS id = GRHS [LStmt id] -- Guards
625 (LHsExpr id) -- Right hand side
628 We know the list must have at least one @Match@ in it.
631 pprMatches :: (OutputableBndr id) => HsMatchContext id -> MatchGroup id -> SDoc
632 pprMatches ctxt (MatchGroup matches ty) = vcat (map (pprMatch ctxt) (map unLoc matches))
633 -- Don't print the type; it's only
634 -- a place-holder before typechecking
636 -- Exported to HsBinds, which can't see the defn of HsMatchContext
637 pprFunBind :: (OutputableBndr id) => id -> MatchGroup id -> SDoc
638 pprFunBind fun matches = pprMatches (FunRhs fun) matches
640 -- Exported to HsBinds, which can't see the defn of HsMatchContext
641 pprPatBind :: (OutputableBndr bndr, OutputableBndr id)
642 => LPat bndr -> GRHSs id -> SDoc
643 pprPatBind pat grhss = sep [ppr pat, nest 4 (pprGRHSs PatBindRhs grhss)]
646 pprMatch :: OutputableBndr id => HsMatchContext id -> Match id -> SDoc
647 pprMatch ctxt (Match pats maybe_ty grhss)
648 = pp_name ctxt <+> sep [sep (map ppr pats),
650 nest 2 (pprGRHSs ctxt grhss)]
652 pp_name (FunRhs fun) = ppr fun -- Not pprBndr; the AbsBinds will
653 -- have printed the signature
654 pp_name LambdaExpr = char '\\'
655 pp_name other = empty
657 ppr_maybe_ty = case maybe_ty of
658 Just ty -> dcolon <+> ppr ty
662 pprGRHSs :: OutputableBndr id => HsMatchContext id -> GRHSs id -> SDoc
663 pprGRHSs ctxt (GRHSs grhss binds)
664 = vcat (map (pprGRHS ctxt . unLoc) grhss)
666 (if isEmptyLocalBinds binds then empty
667 else text "where" $$ nest 4 (pprBinds binds))
669 pprGRHS :: OutputableBndr id => HsMatchContext id -> GRHS id -> SDoc
671 pprGRHS ctxt (GRHS [] expr)
674 pprGRHS ctxt (GRHS guards expr)
675 = sep [char '|' <+> interpp'SP guards, pp_rhs ctxt expr]
677 pp_rhs ctxt rhs = matchSeparator ctxt <+> pprDeeper (ppr rhs)
680 %************************************************************************
682 \subsection{Do stmts and list comprehensions}
684 %************************************************************************
687 type LStmt id = Located (Stmt id)
689 -- The SyntaxExprs in here are used *only* for do-notation, which
690 -- has rebindable syntax. Otherwise they are unused.
694 (SyntaxExpr id) -- The (>>=) operator
695 (SyntaxExpr id) -- The fail operator
696 -- The fail operator is noSyntaxExpr
697 -- if the pattern match can't fail
699 | ExprStmt (LHsExpr id)
700 (SyntaxExpr id) -- The (>>) operator
701 PostTcType -- Element type of the RHS (used for arrows)
703 | LetStmt (HsLocalBinds id)
705 -- ParStmts only occur in a list comprehension
706 | ParStmt [([LStmt id], [id])] -- After renaming, the ids are the binders
707 -- bound by the stmts and used subsequently
709 -- Recursive statement (see Note [RecStmt] below)
711 --- The next two fields are only valid after renaming
712 [id] -- The ids are a subset of the variables bound by the stmts
713 -- that are used in stmts that follow the RecStmt
715 [id] -- Ditto, but these variables are the "recursive" ones, that
716 -- are used before they are bound in the stmts of the RecStmt
717 -- From a type-checking point of view, these ones have to be monomorphic
719 --- These fields are only valid after typechecking
720 [PostTcExpr] -- These expressions correspond
721 -- 1-to-1 with the "recursive" [id], and are the expresions that
722 -- should be returned by the recursion. They may not quite be the
723 -- Ids themselves, because the Id may be *polymorphic*, but
724 -- the returned thing has to be *monomorphic*.
725 (DictBinds id) -- Method bindings of Ids bound by the RecStmt,
726 -- and used afterwards
729 ExprStmts are a bit tricky, because what they mean
730 depends on the context. Consider the following contexts:
732 A do expression of type (m res_ty)
733 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
734 * ExprStmt E any_ty: do { ....; E; ... }
736 Translation: E >> ...
738 A list comprehensions of type [elt_ty]
739 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
740 * ExprStmt E Bool: [ .. | .... E ]
742 [ .. | .... | ..., E | ... ]
744 Translation: if E then fail else ...
746 A guard list, guarding a RHS of type rhs_ty
747 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
748 * ExprStmt E Bool: f x | ..., E, ... = ...rhs...
750 Translation: if E then fail else ...
752 Array comprehensions are handled like list comprehensions -=chak
759 , RecStmt [a::forall a. a -> a, b]
761 [ BindStmt b (return x)
767 Here, the RecStmt binds a,b,c; but
768 - Only a,b are used in the stmts *following* the RecStmt,
769 This 'a' is *polymorphic'
770 - Only a,c are used in the stmts *inside* the RecStmt
771 *before* their bindings
772 This 'a' is monomorphic
774 Nota Bene: the two a's have different types, even though they
779 instance OutputableBndr id => Outputable (Stmt id) where
780 ppr stmt = pprStmt stmt
782 pprStmt (BindStmt pat expr _ _) = hsep [ppr pat, ptext SLIT("<-"), ppr expr]
783 pprStmt (LetStmt binds) = hsep [ptext SLIT("let"), pprBinds binds]
784 pprStmt (ExprStmt expr _ _) = ppr expr
785 pprStmt (ParStmt stmtss) = hsep (map (\stmts -> ptext SLIT("| ") <> ppr stmts) stmtss)
786 pprStmt (RecStmt segment _ _ _ _) = ptext SLIT("rec") <+> braces (vcat (map ppr segment))
788 pprDo :: OutputableBndr id => HsStmtContext any -> [LStmt id] -> LHsExpr id -> SDoc
789 pprDo DoExpr stmts body = ptext SLIT("do") <+> (vcat (map ppr stmts) $$ ppr body)
790 pprDo (MDoExpr _) stmts body = ptext SLIT("mdo") <+> (vcat (map ppr stmts) $$ ppr body)
791 pprDo ListComp stmts body = pprComp brackets stmts body
792 pprDo PArrComp stmts body = pprComp pa_brackets stmts body
793 pprDo other stmts body = panic "pprDo" -- PatGuard, ParStmtCxt
795 pprComp :: OutputableBndr id => (SDoc -> SDoc) -> [LStmt id] -> LHsExpr id -> SDoc
796 pprComp brack quals body
798 hang (ppr body <+> char '|')
802 %************************************************************************
804 Template Haskell quotation brackets
806 %************************************************************************
809 data HsSplice id = HsSplice -- $z or $(f 4)
810 id -- The id is just a unique name to
811 (LHsExpr id) -- identify this splice point
813 instance OutputableBndr id => Outputable (HsSplice id) where
816 pprSplice :: OutputableBndr id => HsSplice id -> SDoc
817 pprSplice (HsSplice n e) = char '$' <> brackets (ppr n) <> pprParendExpr e
820 data HsBracket id = ExpBr (LHsExpr id) -- [| expr |]
821 | PatBr (LPat id) -- [p| pat |]
822 | DecBr (HsGroup id) -- [d| decls |]
823 | TypBr (LHsType id) -- [t| type |]
824 | VarBr id -- 'x, ''T
826 instance OutputableBndr id => Outputable (HsBracket id) where
830 pprHsBracket (ExpBr e) = thBrackets empty (ppr e)
831 pprHsBracket (PatBr p) = thBrackets (char 'p') (ppr p)
832 pprHsBracket (DecBr d) = thBrackets (char 'd') (ppr d)
833 pprHsBracket (TypBr t) = thBrackets (char 't') (ppr t)
834 pprHsBracket (VarBr n) = char '\'' <> ppr n
835 -- Infelicity: can't show ' vs '', because
836 -- we can't ask n what its OccName is, because the
837 -- pretty-printer for HsExpr doesn't ask for NamedThings
838 -- But the pretty-printer for names will show the OccName class
840 thBrackets pp_kind pp_body = char '[' <> pp_kind <> char '|' <+>
841 pp_body <+> ptext SLIT("|]")
844 %************************************************************************
846 \subsection{Enumerations and list comprehensions}
848 %************************************************************************
853 | FromThen (LHsExpr id)
855 | FromTo (LHsExpr id)
857 | FromThenTo (LHsExpr id)
863 instance OutputableBndr id => Outputable (ArithSeqInfo id) where
864 ppr (From e1) = hcat [ppr e1, pp_dotdot]
865 ppr (FromThen e1 e2) = hcat [ppr e1, comma, space, ppr e2, pp_dotdot]
866 ppr (FromTo e1 e3) = hcat [ppr e1, pp_dotdot, ppr e3]
867 ppr (FromThenTo e1 e2 e3)
868 = hcat [ppr e1, comma, space, ppr e2, pp_dotdot, ppr e3]
870 pp_dotdot = ptext SLIT(" .. ")
874 %************************************************************************
876 \subsection{HsMatchCtxt}
878 %************************************************************************
881 data HsMatchContext id -- Context of a Match
882 = FunRhs id -- Function binding for f
883 | CaseAlt -- Guard on a case alternative
884 | LambdaExpr -- Pattern of a lambda
885 | ProcExpr -- Pattern of a proc
886 | PatBindRhs -- Pattern binding
887 | RecUpd -- Record update [used only in DsExpr to tell matchWrapper
888 -- what sort of runtime error message to generate]
889 | StmtCtxt (HsStmtContext id) -- Pattern of a do-stmt or list comprehension
892 data HsStmtContext id
895 | MDoExpr PostTcTable -- Recursive do-expression
896 -- (tiresomely, it needs table
897 -- of its return/bind ops)
898 | PArrComp -- Parallel array comprehension
899 | PatGuard (HsMatchContext id) -- Pattern guard for specified thing
900 | ParStmtCtxt (HsStmtContext id) -- A branch of a parallel stmt
904 isDoExpr :: HsStmtContext id -> Bool
905 isDoExpr DoExpr = True
906 isDoExpr (MDoExpr _) = True
907 isDoExpr other = False
911 matchSeparator (FunRhs _) = ptext SLIT("=")
912 matchSeparator CaseAlt = ptext SLIT("->")
913 matchSeparator LambdaExpr = ptext SLIT("->")
914 matchSeparator ProcExpr = ptext SLIT("->")
915 matchSeparator PatBindRhs = ptext SLIT("=")
916 matchSeparator (StmtCtxt _) = ptext SLIT("<-")
917 matchSeparator RecUpd = panic "unused"
921 pprMatchContext (FunRhs fun) = ptext SLIT("the definition of") <+> quotes (ppr fun)
922 pprMatchContext CaseAlt = ptext SLIT("a case alternative")
923 pprMatchContext RecUpd = ptext SLIT("a record-update construct")
924 pprMatchContext PatBindRhs = ptext SLIT("a pattern binding")
925 pprMatchContext LambdaExpr = ptext SLIT("a lambda abstraction")
926 pprMatchContext ProcExpr = ptext SLIT("an arrow abstraction")
927 pprMatchContext (StmtCtxt ctxt) = ptext SLIT("a pattern binding in") $$ pprStmtContext ctxt
929 pprStmtContext (ParStmtCtxt c) = sep [ptext SLIT("a parallel branch of"), pprStmtContext c]
930 pprStmtContext (PatGuard ctxt) = ptext SLIT("a pattern guard for") $$ pprMatchContext ctxt
931 pprStmtContext DoExpr = ptext SLIT("a 'do' expression")
932 pprStmtContext (MDoExpr _) = ptext SLIT("an 'mdo' expression")
933 pprStmtContext ListComp = ptext SLIT("a list comprehension")
934 pprStmtContext PArrComp = ptext SLIT("an array comprehension")
937 pprMatchRhsContext (FunRhs fun) = ptext SLIT("a right-hand side of function") <+> quotes (ppr fun)
938 pprMatchRhsContext CaseAlt = ptext SLIT("the body of a case alternative")
939 pprMatchRhsContext PatBindRhs = ptext SLIT("the right-hand side of a pattern binding")
940 pprMatchRhsContext LambdaExpr = ptext SLIT("the body of a lambda")
941 pprMatchRhsContext ProcExpr = ptext SLIT("the body of a proc")
942 pprMatchRhsContext other = panic "pprMatchRhsContext" -- RecUpd, StmtCtxt
944 -- Used for the result statement of comprehension
945 -- e.g. the 'e' in [ e | ... ]
946 -- or the 'r' in f x = r
947 pprStmtResultContext (PatGuard ctxt) = pprMatchRhsContext ctxt
948 pprStmtResultContext other = ptext SLIT("the result of") <+> pprStmtContext other
951 -- Used to generate the string for a *runtime* error message
952 matchContextErrString (FunRhs fun) = "function " ++ showSDoc (ppr fun)
953 matchContextErrString CaseAlt = "case"
954 matchContextErrString PatBindRhs = "pattern binding"
955 matchContextErrString RecUpd = "record update"
956 matchContextErrString LambdaExpr = "lambda"
957 matchContextErrString ProcExpr = "proc"
958 matchContextErrString (StmtCtxt (ParStmtCtxt c)) = matchContextErrString (StmtCtxt c)
959 matchContextErrString (StmtCtxt (PatGuard _)) = "pattern guard"
960 matchContextErrString (StmtCtxt DoExpr) = "'do' expression"
961 matchContextErrString (StmtCtxt (MDoExpr _)) = "'mdo' expression"
962 matchContextErrString (StmtCtxt ListComp) = "list comprehension"
963 matchContextErrString (StmtCtxt PArrComp) = "array comprehension"