2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[HsExpr]{Abstract Haskell syntax: expressions}
9 #include "HsVersions.h"
12 import HsDecls ( HsGroup )
14 import HsLit ( HsLit(..), HsOverLit )
15 import HsTypes ( LHsType, PostTcType )
16 import HsImpExp ( isOperator, pprHsVar )
17 import HsBinds ( HsLocalBinds, DictBinds, ExprCoFn, isEmptyLocalBinds )
20 import Type ( Type, pprParendType )
21 import Var ( TyVar, Id )
23 import BasicTypes ( IPName, Boxity, tupleParens, Arity, Fixity(..) )
24 import SrcLoc ( Located(..), unLoc )
30 %************************************************************************
32 \subsection{Expressions proper}
34 %************************************************************************
37 type LHsExpr id = Located (HsExpr id)
39 -------------------------
40 -- PostTcExpr is an evidence expression attached to the
41 -- syntax tree by the type checker (c.f. postTcType)
42 -- We use a PostTcTable where there are a bunch of pieces of
43 -- evidence, more than is convenient to keep individually
44 type PostTcExpr = HsExpr Id
45 type PostTcTable = [(Name, Id)]
47 noPostTcExpr :: PostTcExpr
48 noPostTcExpr = HsLit (HsString FSLIT("noPostTcExpr"))
50 noPostTcTable :: PostTcTable
53 -------------------------
54 -- SyntaxExpr is like PostTcExpr, but it's filled in a little earlier,
55 -- by the renamer. It's used for rebindable syntax.
56 -- E.g. (>>=) is filled in before the renamer by the appropriate Name
57 -- for (>>=), and then instantiated by the type checker with its
60 type SyntaxExpr id = HsExpr id
62 noSyntaxExpr :: SyntaxExpr id -- Before renaming, and sometimes after,
63 -- (if the syntax slot makes no sense)
64 noSyntaxExpr = HsLit (HsString FSLIT("noSyntaxExpr"))
67 type SyntaxTable id = [(Name, SyntaxExpr id)]
68 -- *** Currently used only for CmdTop (sigh) ***
69 -- * Before the renamer, this list is noSyntaxTable
71 -- * After the renamer, it takes the form [(std_name, HsVar actual_name)]
72 -- For example, for the 'return' op of a monad
73 -- normal case: (GHC.Base.return, HsVar GHC.Base.return)
74 -- with rebindable syntax: (GHC.Base.return, return_22)
75 -- where return_22 is whatever "return" is in scope
77 -- * After the type checker, it takes the form [(std_name, <expression>)]
78 -- where <expression> is the evidence for the method
80 noSyntaxTable :: SyntaxTable id
84 -------------------------
86 = HsVar id -- variable
87 | HsIPVar (IPName id) -- implicit parameter
88 | HsOverLit (HsOverLit id) -- Overloaded literals
89 | HsLit HsLit -- Simple (non-overloaded) literals
91 | HsLam (MatchGroup id) -- Currently always a single match
93 | HsApp (LHsExpr id) -- Application
96 -- Operator applications:
97 -- NB Bracketed ops such as (+) come out as Vars.
99 -- NB We need an expr for the operator in an OpApp/Section since
100 -- the typechecker may need to apply the operator to a few types.
102 | OpApp (LHsExpr id) -- left operand
103 (LHsExpr id) -- operator
104 Fixity -- Renamer adds fixity; bottom until then
105 (LHsExpr id) -- right operand
107 | NegApp (LHsExpr id) -- negated expr
108 (SyntaxExpr id) -- Name of 'negate'
110 | HsPar (LHsExpr id) -- parenthesised expr
112 | SectionL (LHsExpr id) -- operand
113 (LHsExpr id) -- operator
114 | SectionR (LHsExpr id) -- operator
115 (LHsExpr id) -- operand
117 | HsCase (LHsExpr id)
120 | HsIf (LHsExpr id) -- predicate
121 (LHsExpr id) -- then part
122 (LHsExpr id) -- else part
124 | HsLet (HsLocalBinds id) -- let(rec)
127 | HsDo (HsStmtContext Name) -- The parameterisation is unimportant
128 -- because in this context we never use
129 -- the PatGuard or ParStmt variant
130 [LStmt id] -- "do":one or more stmts
131 (LHsExpr id) -- The body; the last expression in the 'do'
132 -- of [ body | ... ] in a list comp
133 PostTcType -- Type of the whole expression
135 | ExplicitList -- syntactic list
136 PostTcType -- Gives type of components of list
139 | ExplicitPArr -- syntactic parallel array: [:e1, ..., en:]
140 PostTcType -- type of elements of the parallel array
143 | ExplicitTuple -- tuple
145 -- NB: Unit is ExplicitTuple []
146 -- for tuples, we can get the types
147 -- direct from the components
151 -- Record construction
152 | RecordCon (Located id) -- The constructor. After type checking
153 -- it's the dataConWrapId of the constructor
154 PostTcExpr -- Data con Id applied to type args
158 | RecordUpd (LHsExpr id)
160 PostTcType -- Type of *input* record
161 PostTcType -- Type of *result* record (may differ from
162 -- type of input record)
164 | ExprWithTySig -- e :: type
168 | ExprWithTySigOut -- TRANSLATION
170 (LHsType Name) -- Retain the signature for round-tripping purposes
172 | ArithSeq -- arithmetic sequence
176 | PArrSeq -- arith. sequence for parallel array
177 PostTcExpr -- [:e1..e2:] or [:e1, e2..e3:]
180 | HsSCC FastString -- "set cost centre" (_scc_) annotation
181 (LHsExpr id) -- expr whose cost is to be measured
183 | HsCoreAnn FastString -- hdaume: core annotation
186 -----------------------------------------------------------
187 -- MetaHaskell Extensions
188 | HsBracket (HsBracket id)
190 | HsBracketOut (HsBracket Name) -- Output of the type checker is the *original*
191 [PendingSplice] -- renamed expression, plus *typechecked* splices
192 -- to be pasted back in by the desugarer
194 | HsSpliceE (HsSplice id)
196 -----------------------------------------------------------
197 -- Arrow notation extension
199 | HsProc (LPat id) -- arrow abstraction, proc
200 (LHsCmdTop id) -- body of the abstraction
201 -- always has an empty stack
203 ---------------------------------------
204 -- The following are commands, not expressions proper
206 | HsArrApp -- Arrow tail, or arrow application (f -< arg)
207 (LHsExpr id) -- arrow expression, f
208 (LHsExpr id) -- input expression, arg
209 PostTcType -- type of the arrow expressions f,
210 -- of the form a t t', where arg :: t
211 HsArrAppType -- higher-order (-<<) or first-order (-<)
212 Bool -- True => right-to-left (f -< arg)
213 -- False => left-to-right (arg >- f)
215 | HsArrForm -- Command formation, (| e cmd1 .. cmdn |)
216 (LHsExpr id) -- the operator
217 -- after type-checking, a type abstraction to be
218 -- applied to the type of the local environment tuple
219 (Maybe Fixity) -- fixity (filled in by the renamer), for forms that
220 -- were converted from OpApp's by the renamer
221 [LHsCmdTop id] -- argument commands
225 These constructors only appear temporarily in the parser.
226 The renamer translates them into the Right Thing.
229 | EWildPat -- wildcard
231 | EAsPat (Located id) -- as pattern
234 | ELazyPat (LHsExpr id) -- ~ pattern
236 | HsType (LHsType id) -- Explicit type argument; e.g f {| Int |} x y
239 Everything from here on appears only in typechecker output.
242 | TyLam -- TRANSLATION
245 | TyApp -- TRANSLATION
246 (LHsExpr id) -- generated by Spec
249 -- DictLam and DictApp are "inverses"
257 | HsCoerce ExprCoFn -- TRANSLATION
260 type PendingSplice = (Name, LHsExpr Id) -- Typechecked splices, waiting to be
261 -- pasted back in by the desugarer
264 A @Dictionary@, unless of length 0 or 1, becomes a tuple. A
265 @ClassDictLam dictvars methods expr@ is, therefore:
267 \ x -> case x of ( dictvars-and-methods-tuple ) -> expr
271 instance OutputableBndr id => Outputable (HsExpr id) where
272 ppr expr = pprExpr expr
276 pprExpr :: OutputableBndr id => HsExpr id -> SDoc
278 pprExpr e = pprDeeper (ppr_expr e)
280 pprBinds :: OutputableBndr id => HsLocalBinds id -> SDoc
281 pprBinds b = pprDeeper (ppr b)
283 ppr_lexpr :: OutputableBndr id => LHsExpr id -> SDoc
284 ppr_lexpr e = ppr_expr (unLoc e)
286 ppr_expr (HsVar v) = pprHsVar v
287 ppr_expr (HsIPVar v) = ppr v
288 ppr_expr (HsLit lit) = ppr lit
289 ppr_expr (HsOverLit lit) = ppr lit
291 ppr_expr (HsApp e1 e2)
292 = let (fun, args) = collect_args e1 [e2] in
293 (ppr_lexpr fun) <+> (sep (map pprParendExpr args))
295 collect_args (L _ (HsApp fun arg)) args = collect_args fun (arg:args)
296 collect_args fun args = (fun, args)
298 ppr_expr (OpApp e1 op fixity e2)
300 HsVar v -> pp_infixly v
303 pp_e1 = pprParendExpr e1 -- Add parens to make precedence clear
304 pp_e2 = pprParendExpr e2
307 = hang (ppr op) 4 (sep [pp_e1, pp_e2])
310 = sep [pp_e1, hsep [pprInfix v, pp_e2]]
312 ppr_expr (NegApp e _) = char '-' <+> pprParendExpr e
314 ppr_expr (HsPar e) = parens (ppr_lexpr 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 (TyLam tyvars expr)
396 = hang (hsep [ptext SLIT("/\\"),
397 hsep (map (pprBndr LambdaBind) tyvars),
401 ppr_expr (TyApp expr [ty])
402 = hang (ppr_lexpr expr) 4 (pprParendType ty)
404 ppr_expr (TyApp expr tys)
405 = hang (ppr_lexpr expr)
406 4 (brackets (interpp'SP tys))
408 ppr_expr (DictLam dictvars expr)
409 = hang (hsep [ptext SLIT("\\{-dict-}"),
410 hsep (map (pprBndr LambdaBind) dictvars),
414 ppr_expr (DictApp expr [dname])
415 = hang (ppr_lexpr expr) 4 (ppr dname)
417 ppr_expr (DictApp expr dnames)
418 = hang (ppr_lexpr expr)
419 4 (brackets (interpp'SP dnames))
421 ppr_expr (HsCoerce co_fn e) = ppr_expr e
423 ppr_expr (HsType id) = ppr id
425 ppr_expr (HsSpliceE s) = pprSplice s
426 ppr_expr (HsBracket b) = pprHsBracket b
427 ppr_expr (HsBracketOut e []) = ppr e
428 ppr_expr (HsBracketOut e ps) = ppr e $$ ptext SLIT("pending") <+> ppr ps
430 ppr_expr (HsProc pat (L _ (HsCmdTop cmd _ _ _)))
431 = hsep [ptext SLIT("proc"), ppr pat, ptext SLIT("->"), ppr cmd]
433 ppr_expr (HsArrApp arrow arg _ HsFirstOrderApp True)
434 = hsep [ppr_lexpr arrow, ptext SLIT("-<"), ppr_lexpr arg]
435 ppr_expr (HsArrApp arrow arg _ HsFirstOrderApp False)
436 = hsep [ppr_lexpr arg, ptext SLIT(">-"), ppr_lexpr arrow]
437 ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp True)
438 = hsep [ppr_lexpr arrow, ptext SLIT("-<<"), ppr_lexpr arg]
439 ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp False)
440 = hsep [ppr_lexpr arg, ptext SLIT(">>-"), ppr_lexpr arrow]
442 ppr_expr (HsArrForm (L _ (HsVar v)) (Just _) [arg1, arg2])
443 = sep [pprCmdArg (unLoc arg1), hsep [pprInfix v, pprCmdArg (unLoc arg2)]]
444 ppr_expr (HsArrForm op _ args)
445 = hang (ptext SLIT("(|") <> ppr_lexpr op)
446 4 (sep (map (pprCmdArg.unLoc) args) <> ptext SLIT("|)"))
448 pprCmdArg :: OutputableBndr id => HsCmdTop id -> SDoc
449 pprCmdArg (HsCmdTop cmd@(L _ (HsArrForm _ Nothing [])) _ _ _)
451 pprCmdArg (HsCmdTop cmd _ _ _)
452 = parens (ppr_lexpr cmd)
454 -- Put a var in backquotes if it's not an operator already
455 pprInfix :: Outputable name => name -> SDoc
456 pprInfix v | isOperator ppr_v = ppr_v
457 | otherwise = char '`' <> ppr_v <> char '`'
461 -- add parallel array brackets around a document
463 pa_brackets :: SDoc -> SDoc
464 pa_brackets p = ptext SLIT("[:") <> p <> ptext SLIT(":]")
467 Parenthesize unless very simple:
469 pprParendExpr :: OutputableBndr id => LHsExpr id -> SDoc
472 pp_as_was = ppr_lexpr expr
473 -- Using ppr_expr here avoids the call to 'deeper'
474 -- Not sure if that's always right.
481 HsIPVar _ -> pp_as_was
482 ExplicitList _ _ -> pp_as_was
483 ExplicitPArr _ _ -> pp_as_was
484 ExplicitTuple _ _ -> pp_as_was
486 HsBracket _ -> pp_as_was
487 HsBracketOut _ [] -> pp_as_was
489 _ -> parens pp_as_was
492 %************************************************************************
494 \subsection{Commands (in arrow abstractions)}
496 %************************************************************************
498 We re-use HsExpr to represent these.
501 type HsCmd id = HsExpr id
503 type LHsCmd id = LHsExpr id
505 data HsArrAppType = HsHigherOrderApp | HsFirstOrderApp
508 The legal constructors for commands are:
510 = HsArrApp ... -- as above
512 | HsArrForm ... -- as above
517 | HsLam (Match id) -- kappa
519 -- the renamer turns this one into HsArrForm
520 | OpApp (HsExpr id) -- left operand
521 (HsCmd id) -- operator
522 Fixity -- Renamer adds fixity; bottom until then
523 (HsCmd id) -- right operand
525 | HsPar (HsCmd id) -- parenthesised command
528 [Match id] -- bodies are HsCmd's
531 | HsIf (HsExpr id) -- predicate
532 (HsCmd id) -- then part
533 (HsCmd id) -- else part
536 | HsLet (HsLocalBinds id) -- let(rec)
539 | HsDo (HsStmtContext Name) -- The parameterisation is unimportant
540 -- because in this context we never use
541 -- the PatGuard or ParStmt variant
542 [Stmt id] -- HsExpr's are really HsCmd's
543 PostTcType -- Type of the whole expression
546 Top-level command, introducing a new arrow.
547 This may occur inside a proc (where the stack is empty) or as an
548 argument of a command-forming operator.
551 type LHsCmdTop id = Located (HsCmdTop id)
554 = HsCmdTop (LHsCmd id)
555 [PostTcType] -- types of inputs on the command's stack
556 PostTcType -- return type of the command
558 -- after type checking:
559 -- names used in the command's desugaring
562 %************************************************************************
564 \subsection{Record binds}
566 %************************************************************************
569 type HsRecordBinds id = [(Located id, LHsExpr id)]
571 recBindFields :: HsRecordBinds id -> [id]
572 recBindFields rbinds = [unLoc field | (field,_) <- rbinds]
574 pp_rbinds :: OutputableBndr id => SDoc -> HsRecordBinds id -> SDoc
575 pp_rbinds thing rbinds
577 4 (braces (sep (punctuate comma (map (pp_rbind) rbinds))))
579 pp_rbind (v, e) = hsep [pprBndr LetBind (unLoc v), char '=', ppr e]
584 %************************************************************************
586 \subsection{@Match@, @GRHSs@, and @GRHS@ datatypes}
588 %************************************************************************
590 @Match@es are sets of pattern bindings and right hand sides for
591 functions, patterns or case branches. For example, if a function @g@
597 then \tr{g} has two @Match@es: @(x,y) = y@ and @((x:ys),y) = y+1@.
599 It is always the case that each element of an @[Match]@ list has the
600 same number of @pats@s inside it. This corresponds to saying that
601 a function defined by pattern matching must have the same number of
602 patterns in each equation.
607 [LMatch id] -- The alternatives
608 PostTcType -- The type is the type of the entire group
609 -- t1 -> ... -> tn -> tr
610 -- where there are n patterns
612 type LMatch id = Located (Match id)
616 [LPat id] -- The patterns
617 (Maybe (LHsType id)) -- A type signature for the result of the match
618 -- Nothing after typechecking
621 matchGroupArity :: MatchGroup id -> Arity
622 matchGroupArity (MatchGroup (match:matches) _)
623 = ASSERT( all ((== n_pats) . length . hsLMatchPats) matches )
624 -- Assertion just checks that all the matches have the same number of pats
627 n_pats = length (hsLMatchPats match)
629 hsLMatchPats :: LMatch id -> [LPat id]
630 hsLMatchPats (L _ (Match pats _ _)) = pats
632 -- GRHSs are used both for pattern bindings and for Matches
634 = GRHSs [LGRHS id] -- Guarded RHSs
635 (HsLocalBinds id) -- The where clause
637 type LGRHS id = Located (GRHS id)
639 data GRHS id = GRHS [LStmt id] -- Guards
640 (LHsExpr id) -- Right hand side
643 We know the list must have at least one @Match@ in it.
646 pprMatches :: (OutputableBndr id) => HsMatchContext id -> MatchGroup id -> SDoc
647 pprMatches ctxt (MatchGroup matches _) = vcat (map (pprMatch ctxt) (map unLoc matches))
649 -- Exported to HsBinds, which can't see the defn of HsMatchContext
650 pprFunBind :: (OutputableBndr id) => id -> MatchGroup id -> SDoc
651 pprFunBind fun matches = pprMatches (FunRhs fun) matches
653 -- Exported to HsBinds, which can't see the defn of HsMatchContext
654 pprPatBind :: (OutputableBndr bndr, OutputableBndr id)
655 => LPat bndr -> GRHSs id -> SDoc
656 pprPatBind pat grhss = sep [ppr pat, nest 4 (pprGRHSs PatBindRhs grhss)]
659 pprMatch :: OutputableBndr id => HsMatchContext id -> Match id -> SDoc
660 pprMatch ctxt (Match pats maybe_ty grhss)
661 = pp_name ctxt <+> sep [sep (map ppr pats),
663 nest 2 (pprGRHSs ctxt grhss)]
665 pp_name (FunRhs fun) = ppr fun -- Not pprBndr; the AbsBinds will
666 -- have printed the signature
667 pp_name LambdaExpr = char '\\'
668 pp_name other = empty
670 ppr_maybe_ty = case maybe_ty of
671 Just ty -> dcolon <+> ppr ty
675 pprGRHSs :: OutputableBndr id => HsMatchContext id -> GRHSs id -> SDoc
676 pprGRHSs ctxt (GRHSs grhss binds)
677 = vcat (map (pprGRHS ctxt . unLoc) grhss)
679 (if isEmptyLocalBinds binds then empty
680 else text "where" $$ nest 4 (pprBinds binds))
682 pprGRHS :: OutputableBndr id => HsMatchContext id -> GRHS id -> SDoc
684 pprGRHS ctxt (GRHS [] expr)
687 pprGRHS ctxt (GRHS guards expr)
688 = sep [char '|' <+> interpp'SP guards, pp_rhs ctxt expr]
690 pp_rhs ctxt rhs = matchSeparator ctxt <+> pprDeeper (ppr rhs)
693 %************************************************************************
695 \subsection{Do stmts and list comprehensions}
697 %************************************************************************
700 type LStmt id = Located (Stmt id)
702 -- The SyntaxExprs in here are used *only* for do-notation, which
703 -- has rebindable syntax. Otherwise they are unused.
707 (SyntaxExpr id) -- The (>>=) operator
708 (SyntaxExpr id) -- The fail operator
709 -- The fail operator is noSyntaxExpr
710 -- if the pattern match can't fail
712 | ExprStmt (LHsExpr id)
713 (SyntaxExpr id) -- The (>>) operator
714 PostTcType -- Element type of the RHS (used for arrows)
716 | LetStmt (HsLocalBinds id)
718 -- ParStmts only occur in a list comprehension
719 | ParStmt [([LStmt id], [id])] -- After renaming, the ids are the binders
720 -- bound by the stmts and used subsequently
722 -- Recursive statement (see Note [RecStmt] below)
724 --- The next two fields are only valid after renaming
725 [id] -- The ids are a subset of the variables bound by the stmts
726 -- that are used in stmts that follow the RecStmt
728 [id] -- Ditto, but these variables are the "recursive" ones, that
729 -- are used before they are bound in the stmts of the RecStmt
730 -- From a type-checking point of view, these ones have to be monomorphic
732 --- These fields are only valid after typechecking
733 [PostTcExpr] -- These expressions correspond
734 -- 1-to-1 with the "recursive" [id], and are the expresions that
735 -- should be returned by the recursion. They may not quite be the
736 -- Ids themselves, because the Id may be *polymorphic*, but
737 -- the returned thing has to be *monomorphic*.
738 (DictBinds id) -- Method bindings of Ids bound by the RecStmt,
739 -- and used afterwards
742 ExprStmts are a bit tricky, because what they mean
743 depends on the context. Consider the following contexts:
745 A do expression of type (m res_ty)
746 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
747 * ExprStmt E any_ty: do { ....; E; ... }
749 Translation: E >> ...
751 A list comprehensions of type [elt_ty]
752 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
753 * ExprStmt E Bool: [ .. | .... E ]
755 [ .. | .... | ..., E | ... ]
757 Translation: if E then fail else ...
759 A guard list, guarding a RHS of type rhs_ty
760 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
761 * ExprStmt E Bool: f x | ..., E, ... = ...rhs...
763 Translation: if E then fail else ...
765 Array comprehensions are handled like list comprehensions -=chak
772 , RecStmt [a::forall a. a -> a, b]
774 [ BindStmt b (return x)
780 Here, the RecStmt binds a,b,c; but
781 - Only a,b are used in the stmts *following* the RecStmt,
782 This 'a' is *polymorphic'
783 - Only a,c are used in the stmts *inside* the RecStmt
784 *before* their bindings
785 This 'a' is monomorphic
787 Nota Bene: the two a's have different types, even though they
792 instance OutputableBndr id => Outputable (Stmt id) where
793 ppr stmt = pprStmt stmt
795 pprStmt (BindStmt pat expr _ _) = hsep [ppr pat, ptext SLIT("<-"), ppr expr]
796 pprStmt (LetStmt binds) = hsep [ptext SLIT("let"), pprBinds binds]
797 pprStmt (ExprStmt expr _ _) = ppr expr
798 pprStmt (ParStmt stmtss) = hsep (map (\stmts -> ptext SLIT("| ") <> ppr stmts) stmtss)
799 pprStmt (RecStmt segment _ _ _ _) = ptext SLIT("rec") <+> braces (vcat (map ppr segment))
801 pprDo :: OutputableBndr id => HsStmtContext any -> [LStmt id] -> LHsExpr id -> SDoc
802 pprDo DoExpr stmts body = hang (ptext SLIT("do")) 2 (vcat (map ppr stmts) $$ ppr body)
803 pprDo (MDoExpr _) stmts body = hang (ptext SLIT("mdo")) 3 (vcat (map ppr stmts) $$ ppr body)
804 pprDo ListComp stmts body = pprComp brackets stmts body
805 pprDo PArrComp stmts body = pprComp pa_brackets stmts body
807 pprComp :: OutputableBndr id => (SDoc -> SDoc) -> [LStmt id] -> LHsExpr id -> SDoc
808 pprComp brack quals body
810 hang (ppr body <+> char '|')
814 %************************************************************************
816 Template Haskell quotation brackets
818 %************************************************************************
821 data HsSplice id = HsSplice -- $z or $(f 4)
822 id -- The id is just a unique name to
823 (LHsExpr id) -- identify this splice point
825 instance OutputableBndr id => Outputable (HsSplice id) where
828 pprSplice :: OutputableBndr id => HsSplice id -> SDoc
829 pprSplice (HsSplice n e) = char '$' <> brackets (ppr n) <> pprParendExpr e
832 data HsBracket id = ExpBr (LHsExpr id) -- [| expr |]
833 | PatBr (LPat id) -- [p| pat |]
834 | DecBr (HsGroup id) -- [d| decls |]
835 | TypBr (LHsType id) -- [t| type |]
836 | VarBr id -- 'x, ''T
838 instance OutputableBndr id => Outputable (HsBracket id) where
842 pprHsBracket (ExpBr e) = thBrackets empty (ppr e)
843 pprHsBracket (PatBr p) = thBrackets (char 'p') (ppr p)
844 pprHsBracket (DecBr d) = thBrackets (char 'd') (ppr d)
845 pprHsBracket (TypBr t) = thBrackets (char 't') (ppr t)
846 pprHsBracket (VarBr n) = char '\'' <> ppr n
847 -- Infelicity: can't show ' vs '', because
848 -- we can't ask n what its OccName is, because the
849 -- pretty-printer for HsExpr doesn't ask for NamedThings
850 -- But the pretty-printer for names will show the OccName class
852 thBrackets pp_kind pp_body = char '[' <> pp_kind <> char '|' <+>
853 pp_body <+> ptext SLIT("|]")
856 %************************************************************************
858 \subsection{Enumerations and list comprehensions}
860 %************************************************************************
865 | FromThen (LHsExpr id)
867 | FromTo (LHsExpr id)
869 | FromThenTo (LHsExpr id)
875 instance OutputableBndr id => Outputable (ArithSeqInfo id) where
876 ppr (From e1) = hcat [ppr e1, pp_dotdot]
877 ppr (FromThen e1 e2) = hcat [ppr e1, comma, space, ppr e2, pp_dotdot]
878 ppr (FromTo e1 e3) = hcat [ppr e1, pp_dotdot, ppr e3]
879 ppr (FromThenTo e1 e2 e3)
880 = hcat [ppr e1, comma, space, ppr e2, pp_dotdot, ppr e3]
882 pp_dotdot = ptext SLIT(" .. ")
886 %************************************************************************
888 \subsection{HsMatchCtxt}
890 %************************************************************************
893 data HsMatchContext id -- Context of a Match
894 = FunRhs id -- Function binding for f
895 | CaseAlt -- Guard on a case alternative
896 | LambdaExpr -- Pattern of a lambda
897 | ProcExpr -- Pattern of a proc
898 | PatBindRhs -- Pattern binding
899 | RecUpd -- Record update [used only in DsExpr to tell matchWrapper
900 -- what sort of runtime error message to generate]
901 | StmtCtxt (HsStmtContext id) -- Pattern of a do-stmt or list comprehension
904 data HsStmtContext id
907 | MDoExpr PostTcTable -- Recursive do-expression
908 -- (tiresomely, it needs table
909 -- of its return/bind ops)
910 | PArrComp -- Parallel array comprehension
911 | PatGuard (HsMatchContext id) -- Pattern guard for specified thing
912 | ParStmtCtxt (HsStmtContext id) -- A branch of a parallel stmt
916 isDoExpr :: HsStmtContext id -> Bool
917 isDoExpr DoExpr = True
918 isDoExpr (MDoExpr _) = True
919 isDoExpr other = False
923 matchSeparator (FunRhs _) = ptext SLIT("=")
924 matchSeparator CaseAlt = ptext SLIT("->")
925 matchSeparator LambdaExpr = ptext SLIT("->")
926 matchSeparator ProcExpr = ptext SLIT("->")
927 matchSeparator PatBindRhs = ptext SLIT("=")
928 matchSeparator (StmtCtxt _) = ptext SLIT("<-")
929 matchSeparator RecUpd = panic "unused"
933 pprMatchContext (FunRhs fun) = ptext SLIT("the definition of") <+> quotes (ppr fun)
934 pprMatchContext CaseAlt = ptext SLIT("a case alternative")
935 pprMatchContext RecUpd = ptext SLIT("a record-update construct")
936 pprMatchContext PatBindRhs = ptext SLIT("a pattern binding")
937 pprMatchContext LambdaExpr = ptext SLIT("a lambda abstraction")
938 pprMatchContext ProcExpr = ptext SLIT("an arrow abstraction")
939 pprMatchContext (StmtCtxt ctxt) = ptext SLIT("a pattern binding in") $$ pprStmtContext ctxt
941 pprMatchRhsContext (FunRhs fun) = ptext SLIT("a right-hand side of function") <+> quotes (ppr fun)
942 pprMatchRhsContext CaseAlt = ptext SLIT("the body of a case alternative")
943 pprMatchRhsContext PatBindRhs = ptext SLIT("the right-hand side of a pattern binding")
944 pprMatchRhsContext LambdaExpr = ptext SLIT("the body of a lambda")
945 pprMatchRhsContext ProcExpr = ptext SLIT("the body of a proc")
946 pprMatchRhsContext RecUpd = panic "pprMatchRhsContext"
948 pprStmtContext (ParStmtCtxt c) = sep [ptext SLIT("a parallel branch of"), pprStmtContext c]
949 pprStmtContext (PatGuard ctxt) = ptext SLIT("a pattern guard for") $$ pprMatchContext ctxt
950 pprStmtContext DoExpr = ptext SLIT("a 'do' expression")
951 pprStmtContext (MDoExpr _) = ptext SLIT("an 'mdo' expression")
952 pprStmtContext ListComp = ptext SLIT("a list comprehension")
953 pprStmtContext PArrComp = ptext SLIT("an array comprehension")
955 -- Used for the result statement of comprehension
956 -- e.g. the 'e' in [ e | ... ]
957 -- or the 'r' in f x = r
958 pprStmtResultContext (PatGuard ctxt) = pprMatchRhsContext ctxt
959 pprStmtResultContext other = ptext SLIT("the result of") <+> pprStmtContext other
962 -- Used to generate the string for a *runtime* error message
963 matchContextErrString (FunRhs fun) = "function " ++ showSDoc (ppr fun)
964 matchContextErrString CaseAlt = "case"
965 matchContextErrString PatBindRhs = "pattern binding"
966 matchContextErrString RecUpd = "record update"
967 matchContextErrString LambdaExpr = "lambda"
968 matchContextErrString ProcExpr = "proc"
969 matchContextErrString (StmtCtxt (ParStmtCtxt c)) = matchContextErrString (StmtCtxt c)
970 matchContextErrString (StmtCtxt (PatGuard _)) = "pattern guard"
971 matchContextErrString (StmtCtxt DoExpr) = "'do' expression"
972 matchContextErrString (StmtCtxt (MDoExpr _)) = "'mdo' expression"
973 matchContextErrString (StmtCtxt ListComp) = "list comprehension"
974 matchContextErrString (StmtCtxt PArrComp) = "array comprehension"