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 | HsTickPragma -- A pragma introduced tick
217 (FastString,(Int,Int),(Int,Int)) -- external span for this tick
220 ---------------------------------------
221 -- The following are commands, not expressions proper
223 | HsArrApp -- Arrow tail, or arrow application (f -< arg)
224 (LHsExpr id) -- arrow expression, f
225 (LHsExpr id) -- input expression, arg
226 PostTcType -- type of the arrow expressions f,
227 -- of the form a t t', where arg :: t
228 HsArrAppType -- higher-order (-<<) or first-order (-<)
229 Bool -- True => right-to-left (f -< arg)
230 -- False => left-to-right (arg >- f)
232 | HsArrForm -- Command formation, (| e cmd1 .. cmdn |)
233 (LHsExpr id) -- the operator
234 -- after type-checking, a type abstraction to be
235 -- applied to the type of the local environment tuple
236 (Maybe Fixity) -- fixity (filled in by the renamer), for forms that
237 -- were converted from OpApp's by the renamer
238 [LHsCmdTop id] -- argument commands
242 These constructors only appear temporarily in the parser.
243 The renamer translates them into the Right Thing.
246 | EWildPat -- wildcard
248 | EAsPat (Located id) -- as pattern
251 | ELazyPat (LHsExpr id) -- ~ pattern
253 | HsType (LHsType id) -- Explicit type argument; e.g f {| Int |} x y
256 Everything from here on 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 :: OutputableBndr id => HsExpr id -> SDoc
280 pprExpr e = pprDeeper (ppr_expr e)
282 pprBinds :: OutputableBndr id => HsLocalBinds id -> SDoc
283 pprBinds b = pprDeeper (ppr b)
285 ppr_lexpr :: OutputableBndr id => LHsExpr id -> SDoc
286 ppr_lexpr e = ppr_expr (unLoc e)
288 ppr_expr (HsVar v) = pprHsVar v
289 ppr_expr (HsIPVar v) = ppr v
290 ppr_expr (HsLit lit) = ppr lit
291 ppr_expr (HsOverLit lit) = ppr lit
292 ppr_expr (HsPar e) = parens (ppr_lexpr e)
294 ppr_expr (HsCoreAnn s e)
295 = vcat [ptext SLIT("HsCoreAnn") <+> ftext s, ppr_lexpr e]
297 ppr_expr (HsApp e1 e2)
298 = let (fun, args) = collect_args e1 [e2] in
299 hang (ppr_lexpr fun) 2 (sep (map pprParendExpr args))
301 collect_args (L _ (HsApp fun arg)) args = collect_args fun (arg:args)
302 collect_args fun args = (fun, args)
304 ppr_expr (OpApp e1 op fixity e2)
306 HsVar v -> pp_infixly v
309 pp_e1 = pprParendExpr e1 -- Add parens to make precedence clear
310 pp_e2 = pprParendExpr e2
313 = hang (ppr op) 2 (sep [pp_e1, pp_e2])
316 = sep [nest 2 pp_e1, pprInfix v, nest 2 pp_e2]
318 ppr_expr (NegApp e _) = char '-' <+> pprParendExpr e
320 ppr_expr (SectionL expr op)
322 HsVar v -> pp_infixly v
325 pp_expr = pprParendExpr expr
327 pp_prefixly = hang (hsep [text " \\ x_ ->", ppr op])
328 4 (hsep [pp_expr, ptext SLIT("x_ )")])
329 pp_infixly v = parens (sep [pp_expr, pprInfix v])
331 ppr_expr (SectionR op expr)
333 HsVar v -> pp_infixly v
336 pp_expr = pprParendExpr expr
338 pp_prefixly = hang (hsep [text "( \\ x_ ->", ppr op, ptext SLIT("x_")])
339 4 ((<>) pp_expr rparen)
341 = parens (sep [pprInfix v, pp_expr])
343 ppr_expr (HsLam matches)
344 = pprMatches LambdaExpr matches
346 ppr_expr (HsCase expr matches)
347 = sep [ sep [ptext SLIT("case"), nest 4 (ppr expr), ptext SLIT("of")],
348 nest 2 (pprMatches CaseAlt matches) ]
350 ppr_expr (HsIf e1 e2 e3)
351 = sep [hsep [ptext SLIT("if"), nest 2 (ppr e1), ptext SLIT("then")],
356 -- special case: let ... in let ...
357 ppr_expr (HsLet binds expr@(L _ (HsLet _ _)))
358 = sep [hang (ptext SLIT("let")) 2 (hsep [pprBinds binds, ptext SLIT("in")]),
361 ppr_expr (HsLet binds expr)
362 = sep [hang (ptext SLIT("let")) 2 (pprBinds binds),
363 hang (ptext SLIT("in")) 2 (ppr expr)]
365 ppr_expr (HsDo do_or_list_comp stmts body _) = pprDo do_or_list_comp stmts body
367 ppr_expr (ExplicitList _ exprs)
368 = brackets (fsep (punctuate comma (map ppr_lexpr exprs)))
370 ppr_expr (ExplicitPArr _ exprs)
371 = pa_brackets (fsep (punctuate comma (map ppr_lexpr exprs)))
373 ppr_expr (ExplicitTuple exprs boxity)
374 = tupleParens boxity (sep (punctuate comma (map ppr_lexpr exprs)))
376 ppr_expr (RecordCon con_id con_expr rbinds)
377 = pp_rbinds (ppr con_id) rbinds
379 ppr_expr (RecordUpd aexp rbinds _ _)
380 = pp_rbinds (pprParendExpr aexp) rbinds
382 ppr_expr (ExprWithTySig expr sig)
383 = hang (nest 2 (ppr_lexpr expr) <+> dcolon)
385 ppr_expr (ExprWithTySigOut expr sig)
386 = hang (nest 2 (ppr_lexpr expr) <+> dcolon)
389 ppr_expr (ArithSeq expr info) = brackets (ppr info)
390 ppr_expr (PArrSeq expr info) = pa_brackets (ppr info)
392 ppr_expr EWildPat = char '_'
393 ppr_expr (ELazyPat e) = char '~' <> pprParendExpr e
394 ppr_expr (EAsPat v e) = ppr v <> char '@' <> pprParendExpr e
396 ppr_expr (HsSCC lbl expr)
397 = sep [ ptext SLIT("_scc_") <+> doubleQuotes (ftext lbl), pprParendExpr expr ]
399 ppr_expr (HsWrap co_fn e) = pprHsWrapper (ppr_expr e) co_fn
400 ppr_expr (HsType id) = ppr id
402 ppr_expr (HsSpliceE s) = pprSplice s
403 ppr_expr (HsBracket b) = pprHsBracket b
404 ppr_expr (HsBracketOut e []) = ppr e
405 ppr_expr (HsBracketOut e ps) = ppr e $$ ptext SLIT("pending") <+> ppr ps
407 ppr_expr (HsProc pat (L _ (HsCmdTop cmd _ _ _)))
408 = hsep [ptext SLIT("proc"), ppr pat, ptext SLIT("->"), ppr cmd]
410 ppr_expr (HsTick tickId exp)
411 = hcat [ptext SLIT("tick<"), ppr tickId,ptext SLIT(">("), ppr exp,ptext SLIT(")")]
412 ppr_expr (HsBinTick tickIdTrue tickIdFalse exp)
413 = hcat [ptext SLIT("bintick<"),
418 ppr exp,ptext SLIT(")")]
419 ppr_expr (HsTickPragma externalSrcLoc exp)
420 = hcat [ptext SLIT("tickpragma<"), ppr externalSrcLoc,ptext SLIT(">("), ppr exp,ptext SLIT(")")]
422 ppr_expr (HsArrApp arrow arg _ HsFirstOrderApp True)
423 = hsep [ppr_lexpr arrow, ptext SLIT("-<"), ppr_lexpr arg]
424 ppr_expr (HsArrApp arrow arg _ HsFirstOrderApp False)
425 = hsep [ppr_lexpr arg, ptext SLIT(">-"), ppr_lexpr arrow]
426 ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp True)
427 = hsep [ppr_lexpr arrow, ptext SLIT("-<<"), ppr_lexpr arg]
428 ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp False)
429 = hsep [ppr_lexpr arg, ptext SLIT(">>-"), ppr_lexpr arrow]
431 ppr_expr (HsArrForm (L _ (HsVar v)) (Just _) [arg1, arg2])
432 = sep [pprCmdArg (unLoc arg1), hsep [pprInfix v, pprCmdArg (unLoc arg2)]]
433 ppr_expr (HsArrForm op _ args)
434 = hang (ptext SLIT("(|") <> ppr_lexpr op)
435 4 (sep (map (pprCmdArg.unLoc) args) <> ptext SLIT("|)"))
437 pprCmdArg :: OutputableBndr id => HsCmdTop id -> SDoc
438 pprCmdArg (HsCmdTop cmd@(L _ (HsArrForm _ Nothing [])) _ _ _)
440 pprCmdArg (HsCmdTop cmd _ _ _)
441 = parens (ppr_lexpr cmd)
443 -- Put a var in backquotes if it's not an operator already
444 pprInfix :: Outputable name => name -> SDoc
445 pprInfix v | isOperator ppr_v = ppr_v
446 | otherwise = char '`' <> ppr_v <> char '`'
450 -- add parallel array brackets around a document
452 pa_brackets :: SDoc -> SDoc
453 pa_brackets p = ptext SLIT("[:") <> p <> ptext SLIT(":]")
456 Parenthesize unless very simple:
458 pprParendExpr :: OutputableBndr id => LHsExpr id -> SDoc
461 pp_as_was = ppr_lexpr expr
462 -- Using ppr_expr here avoids the call to 'deeper'
463 -- Not sure if that's always right.
470 HsIPVar _ -> pp_as_was
471 ExplicitList _ _ -> pp_as_was
472 ExplicitPArr _ _ -> pp_as_was
473 ExplicitTuple _ _ -> pp_as_was
475 HsBracket _ -> pp_as_was
476 HsBracketOut _ [] -> pp_as_was
478 _ -> parens pp_as_was
481 %************************************************************************
483 \subsection{Commands (in arrow abstractions)}
485 %************************************************************************
487 We re-use HsExpr to represent these.
490 type HsCmd id = HsExpr id
492 type LHsCmd id = LHsExpr id
494 data HsArrAppType = HsHigherOrderApp | HsFirstOrderApp
497 The legal constructors for commands are:
499 = HsArrApp ... -- as above
501 | HsArrForm ... -- as above
506 | HsLam (Match id) -- kappa
508 -- the renamer turns this one into HsArrForm
509 | OpApp (HsExpr id) -- left operand
510 (HsCmd id) -- operator
511 Fixity -- Renamer adds fixity; bottom until then
512 (HsCmd id) -- right operand
514 | HsPar (HsCmd id) -- parenthesised command
517 [Match id] -- bodies are HsCmd's
520 | HsIf (HsExpr id) -- predicate
521 (HsCmd id) -- then part
522 (HsCmd id) -- else part
525 | HsLet (HsLocalBinds id) -- let(rec)
528 | HsDo (HsStmtContext Name) -- The parameterisation is unimportant
529 -- because in this context we never use
530 -- the PatGuard or ParStmt variant
531 [Stmt id] -- HsExpr's are really HsCmd's
532 PostTcType -- Type of the whole expression
535 Top-level command, introducing a new arrow.
536 This may occur inside a proc (where the stack is empty) or as an
537 argument of a command-forming operator.
540 type LHsCmdTop id = Located (HsCmdTop id)
543 = HsCmdTop (LHsCmd id)
544 [PostTcType] -- types of inputs on the command's stack
545 PostTcType -- return type of the command
547 -- after type checking:
548 -- names used in the command's desugaring
551 %************************************************************************
553 \subsection{Record binds}
555 %************************************************************************
558 type HsRecordBinds id = [(Located id, LHsExpr id)]
560 recBindFields :: HsRecordBinds id -> [id]
561 recBindFields rbinds = [unLoc field | (field,_) <- rbinds]
563 pp_rbinds :: OutputableBndr id => SDoc -> HsRecordBinds id -> SDoc
564 pp_rbinds thing rbinds
566 4 (braces (sep (punctuate comma (map (pp_rbind) rbinds))))
568 pp_rbind (v, e) = hsep [pprBndr LetBind (unLoc v), char '=', ppr e]
573 %************************************************************************
575 \subsection{@Match@, @GRHSs@, and @GRHS@ datatypes}
577 %************************************************************************
579 @Match@es are sets of pattern bindings and right hand sides for
580 functions, patterns or case branches. For example, if a function @g@
586 then \tr{g} has two @Match@es: @(x,y) = y@ and @((x:ys),y) = y+1@.
588 It is always the case that each element of an @[Match]@ list has the
589 same number of @pats@s inside it. This corresponds to saying that
590 a function defined by pattern matching must have the same number of
591 patterns in each equation.
596 [LMatch id] -- The alternatives
597 PostTcType -- The type is the type of the entire group
598 -- t1 -> ... -> tn -> tr
599 -- where there are n patterns
601 type LMatch id = Located (Match id)
605 [LPat id] -- The patterns
606 (Maybe (LHsType id)) -- A type signature for the result of the match
607 -- Nothing after typechecking
610 matchGroupArity :: MatchGroup id -> Arity
611 matchGroupArity (MatchGroup [] _)
612 = panic "matchGroupArity" -- MatchGroup is never empty
613 matchGroupArity (MatchGroup (match:matches) _)
614 = ASSERT( all ((== n_pats) . length . hsLMatchPats) matches )
615 -- Assertion just checks that all the matches have the same number of pats
618 n_pats = length (hsLMatchPats match)
620 hsLMatchPats :: LMatch id -> [LPat id]
621 hsLMatchPats (L _ (Match pats _ _)) = pats
623 -- GRHSs are used both for pattern bindings and for Matches
625 = GRHSs [LGRHS id] -- Guarded RHSs
626 (HsLocalBinds id) -- The where clause
628 type LGRHS id = Located (GRHS id)
630 data GRHS id = GRHS [LStmt id] -- Guards
631 (LHsExpr id) -- Right hand side
634 We know the list must have at least one @Match@ in it.
637 pprMatches :: (OutputableBndr id) => HsMatchContext id -> MatchGroup id -> SDoc
638 pprMatches ctxt (MatchGroup matches ty) = vcat (map (pprMatch ctxt) (map unLoc matches))
639 -- Don't print the type; it's only
640 -- a place-holder before typechecking
642 -- Exported to HsBinds, which can't see the defn of HsMatchContext
643 pprFunBind :: (OutputableBndr id) => id -> MatchGroup id -> SDoc
644 pprFunBind fun matches = pprMatches (FunRhs fun) matches
646 -- Exported to HsBinds, which can't see the defn of HsMatchContext
647 pprPatBind :: (OutputableBndr bndr, OutputableBndr id)
648 => LPat bndr -> GRHSs id -> SDoc
649 pprPatBind pat grhss = sep [ppr pat, nest 4 (pprGRHSs PatBindRhs grhss)]
652 pprMatch :: OutputableBndr id => HsMatchContext id -> Match id -> SDoc
653 pprMatch ctxt (Match pats maybe_ty grhss)
654 = pp_name ctxt <+> sep [sep (map ppr pats),
656 nest 2 (pprGRHSs ctxt grhss)]
658 pp_name (FunRhs fun) = ppr fun -- Not pprBndr; the AbsBinds will
659 -- have printed the signature
660 pp_name LambdaExpr = char '\\'
661 pp_name other = empty
663 ppr_maybe_ty = case maybe_ty of
664 Just ty -> dcolon <+> ppr ty
668 pprGRHSs :: OutputableBndr id => HsMatchContext id -> GRHSs id -> SDoc
669 pprGRHSs ctxt (GRHSs grhss binds)
670 = vcat (map (pprGRHS ctxt . unLoc) grhss)
672 (if isEmptyLocalBinds binds then empty
673 else text "where" $$ nest 4 (pprBinds binds))
675 pprGRHS :: OutputableBndr id => HsMatchContext id -> GRHS id -> SDoc
677 pprGRHS ctxt (GRHS [] expr)
680 pprGRHS ctxt (GRHS guards expr)
681 = sep [char '|' <+> interpp'SP guards, pp_rhs ctxt expr]
683 pp_rhs ctxt rhs = matchSeparator ctxt <+> pprDeeper (ppr rhs)
686 %************************************************************************
688 \subsection{Do stmts and list comprehensions}
690 %************************************************************************
693 type LStmt id = Located (Stmt id)
695 -- The SyntaxExprs in here are used *only* for do-notation, which
696 -- has rebindable syntax. Otherwise they are unused.
700 (SyntaxExpr id) -- The (>>=) operator
701 (SyntaxExpr id) -- The fail operator
702 -- The fail operator is noSyntaxExpr
703 -- if the pattern match can't fail
705 | ExprStmt (LHsExpr id)
706 (SyntaxExpr id) -- The (>>) operator
707 PostTcType -- Element type of the RHS (used for arrows)
709 | LetStmt (HsLocalBinds id)
711 -- ParStmts only occur in a list comprehension
712 | ParStmt [([LStmt id], [id])] -- After renaming, the ids are the binders
713 -- bound by the stmts and used subsequently
715 -- Recursive statement (see Note [RecStmt] below)
717 --- The next two fields are only valid after renaming
718 [id] -- The ids are a subset of the variables bound by the stmts
719 -- that are used in stmts that follow the RecStmt
721 [id] -- Ditto, but these variables are the "recursive" ones, that
722 -- are used before they are bound in the stmts of the RecStmt
723 -- From a type-checking point of view, these ones have to be monomorphic
725 --- These fields are only valid after typechecking
726 [PostTcExpr] -- These expressions correspond
727 -- 1-to-1 with the "recursive" [id], and are the expresions that
728 -- should be returned by the recursion. They may not quite be the
729 -- Ids themselves, because the Id may be *polymorphic*, but
730 -- the returned thing has to be *monomorphic*.
731 (DictBinds id) -- Method bindings of Ids bound by the RecStmt,
732 -- and used afterwards
735 ExprStmts are a bit tricky, because what they mean
736 depends on the context. Consider the following contexts:
738 A do expression of type (m res_ty)
739 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
740 * ExprStmt E any_ty: do { ....; E; ... }
742 Translation: E >> ...
744 A list comprehensions of type [elt_ty]
745 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
746 * ExprStmt E Bool: [ .. | .... E ]
748 [ .. | .... | ..., E | ... ]
750 Translation: if E then fail else ...
752 A guard list, guarding a RHS of type rhs_ty
753 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
754 * ExprStmt E Bool: f x | ..., E, ... = ...rhs...
756 Translation: if E then fail else ...
758 Array comprehensions are handled like list comprehensions -=chak
765 , RecStmt [a::forall a. a -> a, b]
767 [ BindStmt b (return x)
773 Here, the RecStmt binds a,b,c; but
774 - Only a,b are used in the stmts *following* the RecStmt,
775 This 'a' is *polymorphic'
776 - Only a,c are used in the stmts *inside* the RecStmt
777 *before* their bindings
778 This 'a' is monomorphic
780 Nota Bene: the two a's have different types, even though they
785 instance OutputableBndr id => Outputable (Stmt id) where
786 ppr stmt = pprStmt stmt
788 pprStmt (BindStmt pat expr _ _) = hsep [ppr pat, ptext SLIT("<-"), ppr expr]
789 pprStmt (LetStmt binds) = hsep [ptext SLIT("let"), pprBinds binds]
790 pprStmt (ExprStmt expr _ _) = ppr expr
791 pprStmt (ParStmt stmtss) = hsep (map (\stmts -> ptext SLIT("| ") <> ppr stmts) stmtss)
792 pprStmt (RecStmt segment _ _ _ _) = ptext SLIT("rec") <+> braces (vcat (map ppr segment))
794 pprDo :: OutputableBndr id => HsStmtContext any -> [LStmt id] -> LHsExpr id -> SDoc
795 pprDo DoExpr stmts body = ptext SLIT("do") <+> (vcat (map ppr stmts) $$ ppr body)
796 pprDo (MDoExpr _) stmts body = ptext SLIT("mdo") <+> (vcat (map ppr stmts) $$ ppr body)
797 pprDo ListComp stmts body = pprComp brackets stmts body
798 pprDo PArrComp stmts body = pprComp pa_brackets stmts body
799 pprDo other stmts body = panic "pprDo" -- PatGuard, ParStmtCxt
801 pprComp :: OutputableBndr id => (SDoc -> SDoc) -> [LStmt id] -> LHsExpr id -> SDoc
802 pprComp brack quals body
804 hang (ppr body <+> char '|')
808 %************************************************************************
810 Template Haskell quotation brackets
812 %************************************************************************
815 data HsSplice id = HsSplice -- $z or $(f 4)
816 id -- The id is just a unique name to
817 (LHsExpr id) -- identify this splice point
819 instance OutputableBndr id => Outputable (HsSplice id) where
822 pprSplice :: OutputableBndr id => HsSplice id -> SDoc
823 pprSplice (HsSplice n e) = char '$' <> brackets (ppr n) <> pprParendExpr e
826 data HsBracket id = ExpBr (LHsExpr id) -- [| expr |]
827 | PatBr (LPat id) -- [p| pat |]
828 | DecBr (HsGroup id) -- [d| decls |]
829 | TypBr (LHsType id) -- [t| type |]
830 | VarBr id -- 'x, ''T
832 instance OutputableBndr id => Outputable (HsBracket id) where
836 pprHsBracket (ExpBr e) = thBrackets empty (ppr e)
837 pprHsBracket (PatBr p) = thBrackets (char 'p') (ppr p)
838 pprHsBracket (DecBr d) = thBrackets (char 'd') (ppr d)
839 pprHsBracket (TypBr t) = thBrackets (char 't') (ppr t)
840 pprHsBracket (VarBr n) = char '\'' <> ppr n
841 -- Infelicity: can't show ' vs '', because
842 -- we can't ask n what its OccName is, because the
843 -- pretty-printer for HsExpr doesn't ask for NamedThings
844 -- But the pretty-printer for names will show the OccName class
846 thBrackets pp_kind pp_body = char '[' <> pp_kind <> char '|' <+>
847 pp_body <+> ptext SLIT("|]")
850 %************************************************************************
852 \subsection{Enumerations and list comprehensions}
854 %************************************************************************
859 | FromThen (LHsExpr id)
861 | FromTo (LHsExpr id)
863 | FromThenTo (LHsExpr id)
869 instance OutputableBndr id => Outputable (ArithSeqInfo id) where
870 ppr (From e1) = hcat [ppr e1, pp_dotdot]
871 ppr (FromThen e1 e2) = hcat [ppr e1, comma, space, ppr e2, pp_dotdot]
872 ppr (FromTo e1 e3) = hcat [ppr e1, pp_dotdot, ppr e3]
873 ppr (FromThenTo e1 e2 e3)
874 = hcat [ppr e1, comma, space, ppr e2, pp_dotdot, ppr e3]
876 pp_dotdot = ptext SLIT(" .. ")
880 %************************************************************************
882 \subsection{HsMatchCtxt}
884 %************************************************************************
887 data HsMatchContext id -- Context of a Match
888 = FunRhs id -- Function binding for f
889 | CaseAlt -- Guard on a case alternative
890 | LambdaExpr -- Pattern of a lambda
891 | ProcExpr -- Pattern of a proc
892 | PatBindRhs -- Pattern binding
893 | RecUpd -- Record update [used only in DsExpr to tell matchWrapper
894 -- what sort of runtime error message to generate]
895 | StmtCtxt (HsStmtContext id) -- Pattern of a do-stmt or list comprehension
898 data HsStmtContext id
901 | MDoExpr PostTcTable -- Recursive do-expression
902 -- (tiresomely, it needs table
903 -- of its return/bind ops)
904 | PArrComp -- Parallel array comprehension
905 | PatGuard (HsMatchContext id) -- Pattern guard for specified thing
906 | ParStmtCtxt (HsStmtContext id) -- A branch of a parallel stmt
910 isDoExpr :: HsStmtContext id -> Bool
911 isDoExpr DoExpr = True
912 isDoExpr (MDoExpr _) = True
913 isDoExpr other = False
917 matchSeparator (FunRhs _) = ptext SLIT("=")
918 matchSeparator CaseAlt = ptext SLIT("->")
919 matchSeparator LambdaExpr = ptext SLIT("->")
920 matchSeparator ProcExpr = ptext SLIT("->")
921 matchSeparator PatBindRhs = ptext SLIT("=")
922 matchSeparator (StmtCtxt _) = ptext SLIT("<-")
923 matchSeparator RecUpd = panic "unused"
927 pprMatchContext (FunRhs fun) = ptext SLIT("the definition of") <+> quotes (ppr fun)
928 pprMatchContext CaseAlt = ptext SLIT("a case alternative")
929 pprMatchContext RecUpd = ptext SLIT("a record-update construct")
930 pprMatchContext PatBindRhs = ptext SLIT("a pattern binding")
931 pprMatchContext LambdaExpr = ptext SLIT("a lambda abstraction")
932 pprMatchContext ProcExpr = ptext SLIT("an arrow abstraction")
933 pprMatchContext (StmtCtxt ctxt) = ptext SLIT("a pattern binding in") $$ pprStmtContext ctxt
935 pprStmtContext (ParStmtCtxt c) = sep [ptext SLIT("a parallel branch of"), pprStmtContext c]
936 pprStmtContext (PatGuard ctxt) = ptext SLIT("a pattern guard for") $$ pprMatchContext ctxt
937 pprStmtContext DoExpr = ptext SLIT("a 'do' expression")
938 pprStmtContext (MDoExpr _) = ptext SLIT("an 'mdo' expression")
939 pprStmtContext ListComp = ptext SLIT("a list comprehension")
940 pprStmtContext PArrComp = ptext SLIT("an array comprehension")
943 pprMatchRhsContext (FunRhs fun) = ptext SLIT("a right-hand side of function") <+> quotes (ppr fun)
944 pprMatchRhsContext CaseAlt = ptext SLIT("the body of a case alternative")
945 pprMatchRhsContext PatBindRhs = ptext SLIT("the right-hand side of a pattern binding")
946 pprMatchRhsContext LambdaExpr = ptext SLIT("the body of a lambda")
947 pprMatchRhsContext ProcExpr = ptext SLIT("the body of a proc")
948 pprMatchRhsContext other = panic "pprMatchRhsContext" -- RecUpd, StmtCtxt
950 -- Used for the result statement of comprehension
951 -- e.g. the 'e' in [ e | ... ]
952 -- or the 'r' in f x = r
953 pprStmtResultContext (PatGuard ctxt) = pprMatchRhsContext ctxt
954 pprStmtResultContext other = ptext SLIT("the result of") <+> pprStmtContext other
957 -- Used to generate the string for a *runtime* error message
958 matchContextErrString (FunRhs fun) = "function " ++ showSDoc (ppr fun)
959 matchContextErrString CaseAlt = "case"
960 matchContextErrString PatBindRhs = "pattern binding"
961 matchContextErrString RecUpd = "record update"
962 matchContextErrString LambdaExpr = "lambda"
963 matchContextErrString ProcExpr = "proc"
964 matchContextErrString (StmtCtxt (ParStmtCtxt c)) = matchContextErrString (StmtCtxt c)
965 matchContextErrString (StmtCtxt (PatGuard _)) = "pattern guard"
966 matchContextErrString (StmtCtxt DoExpr) = "'do' expression"
967 matchContextErrString (StmtCtxt (MDoExpr _)) = "'mdo' expression"
968 matchContextErrString (StmtCtxt ListComp) = "list comprehension"
969 matchContextErrString (StmtCtxt PArrComp) = "array comprehension"