2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 HsExpr: Abstract Haskell syntax: expressions
11 #include "HsVersions.h"
31 %************************************************************************
33 \subsection{Expressions proper}
35 %************************************************************************
38 type LHsExpr id = Located (HsExpr id)
40 -------------------------
41 -- PostTcExpr is an evidence expression attached to the
42 -- syntax tree by the type checker (c.f. postTcType)
43 -- We use a PostTcTable where there are a bunch of pieces of
44 -- evidence, more than is convenient to keep individually
45 type PostTcExpr = HsExpr Id
46 type PostTcTable = [(Name, Id)]
48 noPostTcExpr :: PostTcExpr
49 noPostTcExpr = HsLit (HsString FSLIT("noPostTcExpr"))
51 noPostTcTable :: PostTcTable
54 -------------------------
55 -- SyntaxExpr is like PostTcExpr, but it's filled in a little earlier,
56 -- by the renamer. It's used for rebindable syntax.
57 -- E.g. (>>=) is filled in before the renamer by the appropriate Name
58 -- for (>>=), and then instantiated by the type checker with its
61 type SyntaxExpr id = HsExpr id
63 noSyntaxExpr :: SyntaxExpr id -- Before renaming, and sometimes after,
64 -- (if the syntax slot makes no sense)
65 noSyntaxExpr = HsLit (HsString FSLIT("noSyntaxExpr"))
68 type SyntaxTable id = [(Name, SyntaxExpr id)]
69 -- *** Currently used only for CmdTop (sigh) ***
70 -- * Before the renamer, this list is noSyntaxTable
72 -- * After the renamer, it takes the form [(std_name, HsVar actual_name)]
73 -- For example, for the 'return' op of a monad
74 -- normal case: (GHC.Base.return, HsVar GHC.Base.return)
75 -- with rebindable syntax: (GHC.Base.return, return_22)
76 -- where return_22 is whatever "return" is in scope
78 -- * After the type checker, it takes the form [(std_name, <expression>)]
79 -- where <expression> is the evidence for the method
81 noSyntaxTable :: SyntaxTable id
85 -------------------------
87 = HsVar id -- variable
88 | HsIPVar (IPName id) -- implicit parameter
89 | HsOverLit (HsOverLit id) -- Overloaded literals
90 | HsLit HsLit -- Simple (non-overloaded) literals
92 | HsLam (MatchGroup id) -- Currently always a single match
94 | HsApp (LHsExpr id) -- Application
97 -- Operator applications:
98 -- NB Bracketed ops such as (+) come out as Vars.
100 -- NB We need an expr for the operator in an OpApp/Section since
101 -- the typechecker may need to apply the operator to a few types.
103 | OpApp (LHsExpr id) -- left operand
104 (LHsExpr id) -- operator
105 Fixity -- Renamer adds fixity; bottom until then
106 (LHsExpr id) -- right operand
108 | NegApp (LHsExpr id) -- negated expr
109 (SyntaxExpr id) -- Name of 'negate'
111 | HsPar (LHsExpr id) -- parenthesised expr
113 | SectionL (LHsExpr id) -- operand
114 (LHsExpr id) -- operator
115 | SectionR (LHsExpr id) -- operator
116 (LHsExpr id) -- operand
118 | HsCase (LHsExpr id)
121 | HsIf (LHsExpr id) -- predicate
122 (LHsExpr id) -- then part
123 (LHsExpr id) -- else part
125 | HsLet (HsLocalBinds id) -- let(rec)
128 | HsDo (HsStmtContext Name) -- The parameterisation is unimportant
129 -- because in this context we never use
130 -- the PatGuard or ParStmt variant
131 [LStmt id] -- "do":one or more stmts
132 (LHsExpr id) -- The body; the last expression in the 'do'
133 -- of [ body | ... ] in a list comp
134 PostTcType -- Type of the whole expression
136 | ExplicitList -- syntactic list
137 PostTcType -- Gives type of components of list
140 | ExplicitPArr -- syntactic parallel array: [:e1, ..., en:]
141 PostTcType -- type of elements of the parallel array
144 | ExplicitTuple -- tuple
146 -- NB: Unit is ExplicitTuple []
147 -- for tuples, we can get the types
148 -- direct from the components
152 -- Record construction
153 | RecordCon (Located id) -- The constructor. After type checking
154 -- it's the dataConWrapId of the constructor
155 PostTcExpr -- Data con Id applied to type args
159 | RecordUpd (LHsExpr id)
161 PostTcType -- Type of *input* record
162 PostTcType -- Type of *result* record (may differ from
163 -- type of input record)
165 | ExprWithTySig -- e :: type
169 | ExprWithTySigOut -- TRANSLATION
171 (LHsType Name) -- Retain the signature for round-tripping purposes
173 | ArithSeq -- arithmetic sequence
177 | PArrSeq -- arith. sequence for parallel array
178 PostTcExpr -- [:e1..e2:] or [:e1, e2..e3:]
181 | HsSCC FastString -- "set cost centre" (_scc_) annotation
182 (LHsExpr id) -- expr whose cost is to be measured
184 | HsCoreAnn FastString -- hdaume: core annotation
187 -----------------------------------------------------------
188 -- MetaHaskell Extensions
190 | HsBracket (HsBracket id)
192 | HsBracketOut (HsBracket Name) -- Output of the type checker is the *original*
193 [PendingSplice] -- renamed expression, plus *typechecked* splices
194 -- to be pasted back in by the desugarer
196 | HsSpliceE (HsSplice id)
198 -----------------------------------------------------------
199 -- Arrow notation extension
201 | HsProc (LPat id) -- arrow abstraction, proc
202 (LHsCmdTop id) -- body of the abstraction
203 -- always has an empty stack
205 ---------------------------------------
206 -- The following are commands, not expressions proper
208 | HsArrApp -- Arrow tail, or arrow application (f -< arg)
209 (LHsExpr id) -- arrow expression, f
210 (LHsExpr id) -- input expression, arg
211 PostTcType -- type of the arrow expressions f,
212 -- of the form a t t', where arg :: t
213 HsArrAppType -- higher-order (-<<) or first-order (-<)
214 Bool -- True => right-to-left (f -< arg)
215 -- False => left-to-right (arg >- f)
217 | HsArrForm -- Command formation, (| e cmd1 .. cmdn |)
218 (LHsExpr id) -- the operator
219 -- after type-checking, a type abstraction to be
220 -- applied to the type of the local environment tuple
221 (Maybe Fixity) -- fixity (filled in by the renamer), for forms that
222 -- were converted from OpApp's by the renamer
223 [LHsCmdTop id] -- argument commands
226 ---------------------------------------
227 -- Haskell program coverage (Hpc) Support
230 Int -- module-local tick number
231 (LHsExpr id) -- sub-expression
234 Int -- module-local tick number for True
235 Int -- module-local tick number for False
236 (LHsExpr id) -- sub-expression
238 | HsTickPragma -- A pragma introduced tick
239 (FastString,(Int,Int),(Int,Int)) -- external span for this tick
242 ---------------------------------------
243 -- These constructors only appear temporarily in the parser.
244 -- 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
255 ---------------------------------------
256 -- Finally, HsWrap appears only in typechecker output
258 | HsWrap HsWrapper -- TRANSLATION
261 type PendingSplice = (Name, LHsExpr Id) -- Typechecked splices, waiting to be
262 -- pasted back in by the desugarer
265 A @Dictionary@, unless of length 0 or 1, becomes a tuple. A
266 @ClassDictLam dictvars methods expr@ is, therefore:
268 \ x -> case x of ( dictvars-and-methods-tuple ) -> expr
272 instance OutputableBndr id => Outputable (HsExpr id) where
273 ppr expr = pprExpr expr
277 -- pprExpr and pprLExpr call pprDeeper;
278 -- the underscore versions do not
279 pprExpr :: OutputableBndr id => HsExpr id -> SDoc
280 pprExpr e = pprDeeper (ppr_expr e)
282 pprLExpr :: OutputableBndr id => LHsExpr id -> SDoc
283 pprLExpr e = pprDeeper (ppr_expr (unLoc e))
285 pprBinds :: OutputableBndr id => HsLocalBinds id -> SDoc
286 pprBinds b = pprDeeper (ppr b)
288 ppr_lexpr :: OutputableBndr id => LHsExpr id -> SDoc
289 ppr_lexpr e = ppr_expr (unLoc e)
291 ppr_expr (HsVar v) = pprHsVar v
292 ppr_expr (HsIPVar v) = ppr v
293 ppr_expr (HsLit lit) = ppr lit
294 ppr_expr (HsOverLit lit) = ppr lit
295 ppr_expr (HsPar e) = parens (ppr_lexpr e)
297 ppr_expr (HsCoreAnn s e)
298 = vcat [ptext SLIT("HsCoreAnn") <+> ftext s, ppr_lexpr e]
300 ppr_expr (HsApp e1 e2)
301 = let (fun, args) = collect_args e1 [e2] in
302 hang (ppr_lexpr fun) 2 (sep (map pprParendExpr args))
304 collect_args (L _ (HsApp fun arg)) args = collect_args fun (arg:args)
305 collect_args fun args = (fun, args)
307 ppr_expr (OpApp e1 op fixity e2)
309 HsVar v -> pp_infixly v
312 pp_e1 = pprParendExpr e1 -- Add parens to make precedence clear
313 pp_e2 = pprParendExpr e2
316 = hang (ppr op) 2 (sep [pp_e1, pp_e2])
319 = sep [nest 2 pp_e1, pprInfix v, nest 2 pp_e2]
321 ppr_expr (NegApp e _) = char '-' <+> pprParendExpr e
323 ppr_expr (SectionL expr op)
325 HsVar v -> pp_infixly v
328 pp_expr = pprParendExpr expr
330 pp_prefixly = hang (hsep [text " \\ x_ ->", ppr op])
331 4 (hsep [pp_expr, ptext SLIT("x_ )")])
332 pp_infixly v = parens (sep [pp_expr, pprInfix v])
334 ppr_expr (SectionR op expr)
336 HsVar v -> pp_infixly v
339 pp_expr = pprParendExpr expr
341 pp_prefixly = hang (hsep [text "( \\ x_ ->", ppr op, ptext SLIT("x_")])
342 4 ((<>) pp_expr rparen)
344 = parens (sep [pprInfix v, pp_expr])
346 ppr_expr (HsLam matches)
347 = pprMatches LambdaExpr matches
349 ppr_expr (HsCase expr matches)
350 = sep [ sep [ptext SLIT("case"), nest 4 (ppr expr), ptext SLIT("of")],
351 nest 2 (pprMatches CaseAlt matches) ]
353 ppr_expr (HsIf e1 e2 e3)
354 = sep [hsep [ptext SLIT("if"), nest 2 (ppr e1), ptext SLIT("then")],
359 -- special case: let ... in let ...
360 ppr_expr (HsLet binds expr@(L _ (HsLet _ _)))
361 = sep [hang (ptext SLIT("let")) 2 (hsep [pprBinds binds, ptext SLIT("in")]),
364 ppr_expr (HsLet binds expr)
365 = sep [hang (ptext SLIT("let")) 2 (pprBinds binds),
366 hang (ptext SLIT("in")) 2 (ppr expr)]
368 ppr_expr (HsDo do_or_list_comp stmts body _) = pprDo do_or_list_comp stmts body
370 ppr_expr (ExplicitList _ exprs)
371 = brackets (pprDeeperList fsep (punctuate comma (map ppr_lexpr exprs)))
373 ppr_expr (ExplicitPArr _ exprs)
374 = pa_brackets (pprDeeperList fsep (punctuate comma (map ppr_lexpr exprs)))
376 ppr_expr (ExplicitTuple exprs boxity)
377 = tupleParens boxity (pprDeeperList sep (punctuate comma (map ppr_lexpr exprs)))
379 ppr_expr (RecordCon con_id con_expr rbinds)
380 = pp_rbinds (ppr con_id) rbinds
382 ppr_expr (RecordUpd aexp rbinds _ _)
383 = pp_rbinds (pprParendExpr aexp) rbinds
385 ppr_expr (ExprWithTySig expr sig)
386 = hang (nest 2 (ppr_lexpr expr) <+> dcolon)
388 ppr_expr (ExprWithTySigOut expr sig)
389 = hang (nest 2 (ppr_lexpr expr) <+> dcolon)
392 ppr_expr (ArithSeq expr info) = brackets (ppr info)
393 ppr_expr (PArrSeq expr info) = pa_brackets (ppr info)
395 ppr_expr EWildPat = char '_'
396 ppr_expr (ELazyPat e) = char '~' <> pprParendExpr e
397 ppr_expr (EAsPat v e) = ppr v <> char '@' <> pprParendExpr e
399 ppr_expr (HsSCC lbl expr)
400 = sep [ ptext SLIT("_scc_") <+> doubleQuotes (ftext lbl), pprParendExpr expr ]
402 ppr_expr (HsWrap co_fn e) = pprHsWrapper (ppr_expr e) co_fn
403 ppr_expr (HsType id) = ppr id
405 ppr_expr (HsSpliceE s) = pprSplice s
406 ppr_expr (HsBracket b) = pprHsBracket b
407 ppr_expr (HsBracketOut e []) = ppr e
408 ppr_expr (HsBracketOut e ps) = ppr e $$ ptext SLIT("pending") <+> ppr ps
410 ppr_expr (HsProc pat (L _ (HsCmdTop cmd _ _ _)))
411 = hsep [ptext SLIT("proc"), ppr pat, ptext SLIT("->"), ppr cmd]
413 ppr_expr (HsTick tickId exp)
414 = hcat [ptext SLIT("tick<"), ppr tickId,ptext SLIT(">("), ppr exp,ptext SLIT(")")]
415 ppr_expr (HsBinTick tickIdTrue tickIdFalse exp)
416 = hcat [ptext SLIT("bintick<"),
421 ppr exp,ptext SLIT(")")]
422 ppr_expr (HsTickPragma externalSrcLoc exp)
423 = hcat [ptext SLIT("tickpragma<"), ppr externalSrcLoc,ptext SLIT(">("), ppr exp,ptext SLIT(")")]
425 ppr_expr (HsArrApp arrow arg _ HsFirstOrderApp True)
426 = hsep [ppr_lexpr arrow, ptext SLIT("-<"), ppr_lexpr arg]
427 ppr_expr (HsArrApp arrow arg _ HsFirstOrderApp False)
428 = hsep [ppr_lexpr arg, ptext SLIT(">-"), ppr_lexpr arrow]
429 ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp True)
430 = hsep [ppr_lexpr arrow, ptext SLIT("-<<"), ppr_lexpr arg]
431 ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp False)
432 = hsep [ppr_lexpr arg, ptext SLIT(">>-"), ppr_lexpr arrow]
434 ppr_expr (HsArrForm (L _ (HsVar v)) (Just _) [arg1, arg2])
435 = sep [pprCmdArg (unLoc arg1), hsep [pprInfix v, pprCmdArg (unLoc arg2)]]
436 ppr_expr (HsArrForm op _ args)
437 = hang (ptext SLIT("(|") <> ppr_lexpr op)
438 4 (sep (map (pprCmdArg.unLoc) args) <> ptext SLIT("|)"))
440 pprCmdArg :: OutputableBndr id => HsCmdTop id -> SDoc
441 pprCmdArg (HsCmdTop cmd@(L _ (HsArrForm _ Nothing [])) _ _ _)
443 pprCmdArg (HsCmdTop cmd _ _ _)
444 = parens (ppr_lexpr cmd)
446 -- Put a var in backquotes if it's not an operator already
447 pprInfix :: Outputable name => name -> SDoc
448 pprInfix v | isOperator ppr_v = ppr_v
449 | otherwise = char '`' <> ppr_v <> char '`'
453 -- add parallel array brackets around a document
455 pa_brackets :: SDoc -> SDoc
456 pa_brackets p = ptext SLIT("[:") <> p <> ptext SLIT(":]")
459 Parenthesize unless very simple:
461 pprParendExpr :: OutputableBndr id => LHsExpr id -> SDoc
464 pp_as_was = pprLExpr expr
465 -- Using pprLExpr makes sure that we go 'deeper'
466 -- I think that is usually (always?) right
473 HsIPVar _ -> pp_as_was
474 ExplicitList _ _ -> pp_as_was
475 ExplicitPArr _ _ -> pp_as_was
476 ExplicitTuple _ _ -> pp_as_was
478 HsBracket _ -> pp_as_was
479 HsBracketOut _ [] -> pp_as_was
480 _ -> parens pp_as_was
483 %************************************************************************
485 \subsection{Commands (in arrow abstractions)}
487 %************************************************************************
489 We re-use HsExpr to represent these.
492 type HsCmd id = HsExpr id
494 type LHsCmd id = LHsExpr id
496 data HsArrAppType = HsHigherOrderApp | HsFirstOrderApp
499 The legal constructors for commands are:
501 = HsArrApp ... -- as above
503 | HsArrForm ... -- as above
508 | HsLam (Match id) -- kappa
510 -- the renamer turns this one into HsArrForm
511 | OpApp (HsExpr id) -- left operand
512 (HsCmd id) -- operator
513 Fixity -- Renamer adds fixity; bottom until then
514 (HsCmd id) -- right operand
516 | HsPar (HsCmd id) -- parenthesised command
519 [Match id] -- bodies are HsCmd's
522 | HsIf (HsExpr id) -- predicate
523 (HsCmd id) -- then part
524 (HsCmd id) -- else part
527 | HsLet (HsLocalBinds id) -- let(rec)
530 | HsDo (HsStmtContext Name) -- The parameterisation is unimportant
531 -- because in this context we never use
532 -- the PatGuard or ParStmt variant
533 [Stmt id] -- HsExpr's are really HsCmd's
534 PostTcType -- Type of the whole expression
537 Top-level command, introducing a new arrow.
538 This may occur inside a proc (where the stack is empty) or as an
539 argument of a command-forming operator.
542 type LHsCmdTop id = Located (HsCmdTop id)
545 = HsCmdTop (LHsCmd id)
546 [PostTcType] -- types of inputs on the command's stack
547 PostTcType -- return type of the command
549 -- after type checking:
550 -- names used in the command's desugaring
553 %************************************************************************
555 \subsection{Record binds}
557 %************************************************************************
560 data HsRecordBinds id = HsRecordBinds [(Located id, LHsExpr id)]
562 recBindFields :: HsRecordBinds id -> [id]
563 recBindFields (HsRecordBinds rbinds) = [unLoc field | (field,_) <- rbinds]
565 pp_rbinds :: OutputableBndr id => SDoc -> HsRecordBinds id -> SDoc
566 pp_rbinds thing (HsRecordBinds rbinds)
568 4 (braces (pprDeeperList sep (punctuate comma (map (pp_rbind) rbinds))))
570 pp_rbind (v, e) = hsep [pprBndr LetBind (unLoc v), char '=', ppr e]
575 %************************************************************************
577 \subsection{@Match@, @GRHSs@, and @GRHS@ datatypes}
579 %************************************************************************
581 @Match@es are sets of pattern bindings and right hand sides for
582 functions, patterns or case branches. For example, if a function @g@
588 then \tr{g} has two @Match@es: @(x,y) = y@ and @((x:ys),y) = y+1@.
590 It is always the case that each element of an @[Match]@ list has the
591 same number of @pats@s inside it. This corresponds to saying that
592 a function defined by pattern matching must have the same number of
593 patterns in each equation.
598 [LMatch id] -- The alternatives
599 PostTcType -- The type is the type of the entire group
600 -- t1 -> ... -> tn -> tr
601 -- where there are n patterns
603 type LMatch id = Located (Match id)
607 [LPat id] -- The patterns
608 (Maybe (LHsType id)) -- A type signature for the result of the match
609 -- Nothing after typechecking
612 matchGroupArity :: MatchGroup id -> Arity
613 matchGroupArity (MatchGroup [] _)
614 = panic "matchGroupArity" -- MatchGroup is never empty
615 matchGroupArity (MatchGroup (match:matches) _)
616 = ASSERT( all ((== n_pats) . length . hsLMatchPats) matches )
617 -- Assertion just checks that all the matches have the same number of pats
620 n_pats = length (hsLMatchPats match)
622 hsLMatchPats :: LMatch id -> [LPat id]
623 hsLMatchPats (L _ (Match pats _ _)) = pats
625 -- GRHSs are used both for pattern bindings and for Matches
627 = GRHSs [LGRHS id] -- Guarded RHSs
628 (HsLocalBinds id) -- The where clause
630 type LGRHS id = Located (GRHS id)
632 data GRHS id = GRHS [LStmt id] -- Guards
633 (LHsExpr id) -- Right hand side
636 We know the list must have at least one @Match@ in it.
639 pprMatches :: (OutputableBndr id) => HsMatchContext id -> MatchGroup id -> SDoc
640 pprMatches ctxt (MatchGroup matches ty) = vcat (map (pprMatch ctxt) (map unLoc matches))
641 -- Don't print the type; it's only
642 -- a place-holder before typechecking
644 -- Exported to HsBinds, which can't see the defn of HsMatchContext
645 pprFunBind :: (OutputableBndr id) => id -> MatchGroup id -> SDoc
646 pprFunBind fun matches = pprMatches (FunRhs fun) matches
648 -- Exported to HsBinds, which can't see the defn of HsMatchContext
649 pprPatBind :: (OutputableBndr bndr, OutputableBndr id)
650 => LPat bndr -> GRHSs id -> SDoc
651 pprPatBind pat grhss = sep [ppr pat, nest 4 (pprGRHSs PatBindRhs grhss)]
654 pprMatch :: OutputableBndr id => HsMatchContext id -> Match id -> SDoc
655 pprMatch ctxt (Match pats maybe_ty grhss)
656 = pp_name ctxt <+> sep [sep (map ppr pats),
658 nest 2 (pprGRHSs ctxt grhss)]
660 pp_name (FunRhs fun) = ppr fun -- Not pprBndr; the AbsBinds will
661 -- have printed the signature
662 pp_name LambdaExpr = char '\\'
663 pp_name other = empty
665 ppr_maybe_ty = case maybe_ty of
666 Just ty -> dcolon <+> ppr ty
670 pprGRHSs :: OutputableBndr id => HsMatchContext id -> GRHSs id -> SDoc
671 pprGRHSs ctxt (GRHSs grhss binds)
673 (vcat (map (pprGRHS ctxt . unLoc) grhss)
675 if isEmptyLocalBinds binds then empty
676 else text "where" $$ nest 4 (pprBinds binds))
678 pprGRHS :: OutputableBndr id => HsMatchContext id -> GRHS id -> SDoc
680 pprGRHS ctxt (GRHS [] expr)
683 pprGRHS ctxt (GRHS guards expr)
684 = sep [char '|' <+> interpp'SP guards, pp_rhs ctxt expr]
686 pp_rhs ctxt rhs = matchSeparator ctxt <+> pprDeeper (ppr rhs)
689 %************************************************************************
691 \subsection{Do stmts and list comprehensions}
693 %************************************************************************
696 type LStmt id = Located (Stmt id)
698 -- The SyntaxExprs in here are used *only* for do-notation, which
699 -- has rebindable syntax. Otherwise they are unused.
703 (SyntaxExpr id) -- The (>>=) operator
704 (SyntaxExpr id) -- The fail operator
705 -- The fail operator is noSyntaxExpr
706 -- if the pattern match can't fail
708 | ExprStmt (LHsExpr id)
709 (SyntaxExpr id) -- The (>>) operator
710 PostTcType -- Element type of the RHS (used for arrows)
712 | LetStmt (HsLocalBinds id)
714 -- ParStmts only occur in a list comprehension
715 | ParStmt [([LStmt id], [id])] -- After renaming, the ids are the binders
716 -- bound by the stmts and used subsequently
718 -- Recursive statement (see Note [RecStmt] below)
720 --- The next two fields are only valid after renaming
721 [id] -- The ids are a subset of the variables bound by the stmts
722 -- that are used in stmts that follow the RecStmt
724 [id] -- Ditto, but these variables are the "recursive" ones, that
725 -- are used before they are bound in the stmts of the RecStmt
726 -- From a type-checking point of view, these ones have to be monomorphic
728 --- These fields are only valid after typechecking
729 [PostTcExpr] -- These expressions correspond
730 -- 1-to-1 with the "recursive" [id], and are the expresions that
731 -- should be returned by the recursion. They may not quite be the
732 -- Ids themselves, because the Id may be *polymorphic*, but
733 -- the returned thing has to be *monomorphic*.
734 (DictBinds id) -- Method bindings of Ids bound by the RecStmt,
735 -- and used afterwards
738 ExprStmts are a bit tricky, because what they mean
739 depends on the context. Consider the following contexts:
741 A do expression of type (m res_ty)
742 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
743 * ExprStmt E any_ty: do { ....; E; ... }
745 Translation: E >> ...
747 A list comprehensions of type [elt_ty]
748 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
749 * ExprStmt E Bool: [ .. | .... E ]
751 [ .. | .... | ..., E | ... ]
753 Translation: if E then fail else ...
755 A guard list, guarding a RHS of type rhs_ty
756 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
757 * ExprStmt E Bool: f x | ..., E, ... = ...rhs...
759 Translation: if E then fail else ...
761 Array comprehensions are handled like list comprehensions -=chak
768 , RecStmt [a::forall a. a -> a, b]
770 [ BindStmt b (return x)
776 Here, the RecStmt binds a,b,c; but
777 - Only a,b are used in the stmts *following* the RecStmt,
778 This 'a' is *polymorphic'
779 - Only a,c are used in the stmts *inside* the RecStmt
780 *before* their bindings
781 This 'a' is monomorphic
783 Nota Bene: the two a's have different types, even though they
788 instance OutputableBndr id => Outputable (Stmt id) where
789 ppr stmt = pprStmt stmt
791 pprStmt (BindStmt pat expr _ _) = hsep [ppr pat, ptext SLIT("<-"), ppr expr]
792 pprStmt (LetStmt binds) = hsep [ptext SLIT("let"), pprBinds binds]
793 pprStmt (ExprStmt expr _ _) = ppr expr
794 pprStmt (ParStmt stmtss) = hsep (map (\stmts -> ptext SLIT("| ") <> ppr stmts) stmtss)
795 pprStmt (RecStmt segment _ _ _ _) = ptext SLIT("rec") <+> braces (vcat (map ppr segment))
797 pprDo :: OutputableBndr id => HsStmtContext any -> [LStmt id] -> LHsExpr id -> SDoc
798 pprDo DoExpr stmts body = ptext SLIT("do") <+> pprDeeperList vcat (map ppr stmts ++ [ppr body])
799 pprDo (MDoExpr _) stmts body = ptext SLIT("mdo") <+> pprDeeperList vcat (map ppr stmts ++ [ppr body])
800 pprDo ListComp stmts body = pprComp brackets stmts body
801 pprDo PArrComp stmts body = pprComp pa_brackets stmts body
802 pprDo other stmts body = panic "pprDo" -- PatGuard, ParStmtCxt
804 pprComp :: OutputableBndr id => (SDoc -> SDoc) -> [LStmt id] -> LHsExpr id -> SDoc
805 pprComp brack quals body
807 hang (ppr body <+> char '|')
811 %************************************************************************
813 Template Haskell quotation brackets
815 %************************************************************************
818 data HsSplice id = HsSplice -- $z or $(f 4)
819 id -- The id is just a unique name to
820 (LHsExpr id) -- identify this splice point
822 instance OutputableBndr id => Outputable (HsSplice id) where
825 pprSplice :: OutputableBndr id => HsSplice id -> SDoc
826 pprSplice (HsSplice n e) = char '$' <> brackets (ppr n) <> pprParendExpr e
829 data HsBracket id = ExpBr (LHsExpr id) -- [| expr |]
830 | PatBr (LPat id) -- [p| pat |]
831 | DecBr (HsGroup id) -- [d| decls |]
832 | TypBr (LHsType id) -- [t| type |]
833 | VarBr id -- 'x, ''T
835 instance OutputableBndr id => Outputable (HsBracket id) where
839 pprHsBracket (ExpBr e) = thBrackets empty (ppr e)
840 pprHsBracket (PatBr p) = thBrackets (char 'p') (ppr p)
841 pprHsBracket (DecBr d) = thBrackets (char 'd') (ppr d)
842 pprHsBracket (TypBr t) = thBrackets (char 't') (ppr t)
843 pprHsBracket (VarBr n) = char '\'' <> ppr n
844 -- Infelicity: can't show ' vs '', because
845 -- we can't ask n what its OccName is, because the
846 -- pretty-printer for HsExpr doesn't ask for NamedThings
847 -- But the pretty-printer for names will show the OccName class
849 thBrackets pp_kind pp_body = char '[' <> pp_kind <> char '|' <+>
850 pp_body <+> ptext SLIT("|]")
853 %************************************************************************
855 \subsection{Enumerations and list comprehensions}
857 %************************************************************************
862 | FromThen (LHsExpr id)
864 | FromTo (LHsExpr id)
866 | FromThenTo (LHsExpr id)
872 instance OutputableBndr id => Outputable (ArithSeqInfo id) where
873 ppr (From e1) = hcat [ppr e1, pp_dotdot]
874 ppr (FromThen e1 e2) = hcat [ppr e1, comma, space, ppr e2, pp_dotdot]
875 ppr (FromTo e1 e3) = hcat [ppr e1, pp_dotdot, ppr e3]
876 ppr (FromThenTo e1 e2 e3)
877 = hcat [ppr e1, comma, space, ppr e2, pp_dotdot, ppr e3]
879 pp_dotdot = ptext SLIT(" .. ")
883 %************************************************************************
885 \subsection{HsMatchCtxt}
887 %************************************************************************
890 data HsMatchContext id -- Context of a Match
891 = FunRhs id -- Function binding for f
892 | CaseAlt -- Guard on a case alternative
893 | LambdaExpr -- Pattern of a lambda
894 | ProcExpr -- Pattern of a proc
895 | PatBindRhs -- Pattern binding
896 | RecUpd -- Record update [used only in DsExpr to tell matchWrapper
897 -- what sort of runtime error message to generate]
898 | StmtCtxt (HsStmtContext id) -- Pattern of a do-stmt or list comprehension
901 data HsStmtContext id
904 | MDoExpr PostTcTable -- Recursive do-expression
905 -- (tiresomely, it needs table
906 -- of its return/bind ops)
907 | PArrComp -- Parallel array comprehension
908 | PatGuard (HsMatchContext id) -- Pattern guard for specified thing
909 | ParStmtCtxt (HsStmtContext id) -- A branch of a parallel stmt
913 isDoExpr :: HsStmtContext id -> Bool
914 isDoExpr DoExpr = True
915 isDoExpr (MDoExpr _) = True
916 isDoExpr other = False
920 matchSeparator (FunRhs _) = ptext SLIT("=")
921 matchSeparator CaseAlt = ptext SLIT("->")
922 matchSeparator LambdaExpr = ptext SLIT("->")
923 matchSeparator ProcExpr = ptext SLIT("->")
924 matchSeparator PatBindRhs = ptext SLIT("=")
925 matchSeparator (StmtCtxt _) = ptext SLIT("<-")
926 matchSeparator RecUpd = panic "unused"
930 pprMatchContext (FunRhs fun) = ptext SLIT("the definition of") <+> quotes (ppr fun)
931 pprMatchContext CaseAlt = ptext SLIT("a case alternative")
932 pprMatchContext RecUpd = ptext SLIT("a record-update construct")
933 pprMatchContext PatBindRhs = ptext SLIT("a pattern binding")
934 pprMatchContext LambdaExpr = ptext SLIT("a lambda abstraction")
935 pprMatchContext ProcExpr = ptext SLIT("an arrow abstraction")
936 pprMatchContext (StmtCtxt ctxt) = ptext SLIT("a pattern binding in") $$ pprStmtContext ctxt
938 pprStmtContext (ParStmtCtxt c) = sep [ptext SLIT("a parallel branch of"), pprStmtContext c]
939 pprStmtContext (PatGuard ctxt) = ptext SLIT("a pattern guard for") $$ pprMatchContext ctxt
940 pprStmtContext DoExpr = ptext SLIT("a 'do' expression")
941 pprStmtContext (MDoExpr _) = ptext SLIT("an 'mdo' expression")
942 pprStmtContext ListComp = ptext SLIT("a list comprehension")
943 pprStmtContext PArrComp = ptext SLIT("an array comprehension")
946 pprMatchRhsContext (FunRhs fun) = ptext SLIT("a right-hand side of function") <+> quotes (ppr fun)
947 pprMatchRhsContext CaseAlt = ptext SLIT("the body of a case alternative")
948 pprMatchRhsContext PatBindRhs = ptext SLIT("the right-hand side of a pattern binding")
949 pprMatchRhsContext LambdaExpr = ptext SLIT("the body of a lambda")
950 pprMatchRhsContext ProcExpr = ptext SLIT("the body of a proc")
951 pprMatchRhsContext other = panic "pprMatchRhsContext" -- RecUpd, StmtCtxt
953 -- Used for the result statement of comprehension
954 -- e.g. the 'e' in [ e | ... ]
955 -- or the 'r' in f x = r
956 pprStmtResultContext (PatGuard ctxt) = pprMatchRhsContext ctxt
957 pprStmtResultContext other = ptext SLIT("the result of") <+> pprStmtContext other
960 -- Used to generate the string for a *runtime* error message
961 matchContextErrString (FunRhs fun) = "function " ++ showSDoc (ppr fun)
962 matchContextErrString CaseAlt = "case"
963 matchContextErrString PatBindRhs = "pattern binding"
964 matchContextErrString RecUpd = "record update"
965 matchContextErrString LambdaExpr = "lambda"
966 matchContextErrString ProcExpr = "proc"
967 matchContextErrString (StmtCtxt (ParStmtCtxt c)) = matchContextErrString (StmtCtxt c)
968 matchContextErrString (StmtCtxt (PatGuard _)) = "pattern guard"
969 matchContextErrString (StmtCtxt DoExpr) = "'do' expression"
970 matchContextErrString (StmtCtxt (MDoExpr _)) = "'mdo' expression"
971 matchContextErrString (StmtCtxt ListComp) = "list comprehension"
972 matchContextErrString (StmtCtxt PArrComp) = "array comprehension"