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"
32 %************************************************************************
34 \subsection{Expressions proper}
36 %************************************************************************
39 type LHsExpr id = Located (HsExpr id)
41 -------------------------
42 -- PostTcExpr is an evidence expression attached to the
43 -- syntax tree by the type checker (c.f. postTcType)
44 -- We use a PostTcTable where there are a bunch of pieces of
45 -- evidence, more than is convenient to keep individually
46 type PostTcExpr = HsExpr Id
47 type PostTcTable = [(Name, Id)]
49 noPostTcExpr :: PostTcExpr
50 noPostTcExpr = HsLit (HsString FSLIT("noPostTcExpr"))
52 noPostTcTable :: PostTcTable
55 -------------------------
56 -- SyntaxExpr is like PostTcExpr, but it's filled in a little earlier,
57 -- by the renamer. It's used for rebindable syntax.
58 -- E.g. (>>=) is filled in before the renamer by the appropriate Name
59 -- for (>>=), and then instantiated by the type checker with its
62 type SyntaxExpr id = HsExpr id
64 noSyntaxExpr :: SyntaxExpr id -- Before renaming, and sometimes after,
65 -- (if the syntax slot makes no sense)
66 noSyntaxExpr = HsLit (HsString FSLIT("noSyntaxExpr"))
69 type SyntaxTable id = [(Name, SyntaxExpr id)]
70 -- *** Currently used only for CmdTop (sigh) ***
71 -- * Before the renamer, this list is noSyntaxTable
73 -- * After the renamer, it takes the form [(std_name, HsVar actual_name)]
74 -- For example, for the 'return' op of a monad
75 -- normal case: (GHC.Base.return, HsVar GHC.Base.return)
76 -- with rebindable syntax: (GHC.Base.return, return_22)
77 -- where return_22 is whatever "return" is in scope
79 -- * After the type checker, it takes the form [(std_name, <expression>)]
80 -- where <expression> is the evidence for the method
82 noSyntaxTable :: SyntaxTable id
86 -------------------------
88 = HsVar id -- variable
89 | HsIPVar (IPName id) -- implicit parameter
90 | HsOverLit (HsOverLit id) -- Overloaded literals
91 | HsLit HsLit -- Simple (non-overloaded) literals
93 | HsLam (MatchGroup id) -- Currently always a single match
95 | HsApp (LHsExpr id) -- Application
98 -- Operator applications:
99 -- NB Bracketed ops such as (+) come out as Vars.
101 -- NB We need an expr for the operator in an OpApp/Section since
102 -- the typechecker may need to apply the operator to a few types.
104 | OpApp (LHsExpr id) -- left operand
105 (LHsExpr id) -- operator
106 Fixity -- Renamer adds fixity; bottom until then
107 (LHsExpr id) -- right operand
109 | NegApp (LHsExpr id) -- negated expr
110 (SyntaxExpr id) -- Name of 'negate'
112 | HsPar (LHsExpr id) -- parenthesised expr
114 | SectionL (LHsExpr id) -- operand
115 (LHsExpr id) -- operator
116 | SectionR (LHsExpr id) -- operator
117 (LHsExpr id) -- operand
119 | HsCase (LHsExpr id)
122 | HsIf (LHsExpr id) -- predicate
123 (LHsExpr id) -- then part
124 (LHsExpr id) -- else part
126 | HsLet (HsLocalBinds id) -- let(rec)
129 | HsDo (HsStmtContext Name) -- The parameterisation is unimportant
130 -- because in this context we never use
131 -- the PatGuard or ParStmt variant
132 [LStmt id] -- "do":one or more stmts
133 (LHsExpr id) -- The body; the last expression in the 'do'
134 -- of [ body | ... ] in a list comp
135 PostTcType -- Type of the whole expression
137 | ExplicitList -- syntactic list
138 PostTcType -- Gives type of components of list
141 | ExplicitPArr -- syntactic parallel array: [:e1, ..., en:]
142 PostTcType -- type of elements of the parallel array
145 | ExplicitTuple -- tuple
147 -- NB: Unit is ExplicitTuple []
148 -- for tuples, we can get the types
149 -- direct from the components
153 -- Record construction
154 | RecordCon (Located id) -- The constructor. After type checking
155 -- it's the dataConWrapId of the constructor
156 PostTcExpr -- Data con Id applied to type args
160 | RecordUpd (LHsExpr id)
162 [DataCon] -- Filled in by the type checker to the *non-empty*
163 -- list of DataCons that have all the upd'd fields
164 [PostTcType] -- Argument types of *input* record type
165 [PostTcType] -- and *output* record type
166 -- For a type family, the arg types are of the *instance* tycon, not the family tycon
168 | ExprWithTySig -- e :: type
172 | ExprWithTySigOut -- TRANSLATION
174 (LHsType Name) -- Retain the signature for round-tripping purposes
176 | ArithSeq -- arithmetic sequence
180 | PArrSeq -- arith. sequence for parallel array
181 PostTcExpr -- [:e1..e2:] or [:e1, e2..e3:]
184 | HsSCC FastString -- "set cost centre" (_scc_) annotation
185 (LHsExpr id) -- expr whose cost is to be measured
187 | HsCoreAnn FastString -- hdaume: core annotation
190 -----------------------------------------------------------
191 -- MetaHaskell Extensions
193 | HsBracket (HsBracket id)
195 | HsBracketOut (HsBracket Name) -- Output of the type checker is the *original*
196 [PendingSplice] -- renamed expression, plus *typechecked* splices
197 -- to be pasted back in by the desugarer
199 | HsSpliceE (HsSplice id)
201 -----------------------------------------------------------
202 -- Arrow notation extension
204 | HsProc (LPat id) -- arrow abstraction, proc
205 (LHsCmdTop id) -- body of the abstraction
206 -- always has an empty stack
208 ---------------------------------------
209 -- The following are commands, not expressions proper
211 | HsArrApp -- Arrow tail, or arrow application (f -< arg)
212 (LHsExpr id) -- arrow expression, f
213 (LHsExpr id) -- input expression, arg
214 PostTcType -- type of the arrow expressions f,
215 -- of the form a t t', where arg :: t
216 HsArrAppType -- higher-order (-<<) or first-order (-<)
217 Bool -- True => right-to-left (f -< arg)
218 -- False => left-to-right (arg >- f)
220 | HsArrForm -- Command formation, (| e cmd1 .. cmdn |)
221 (LHsExpr id) -- the operator
222 -- after type-checking, a type abstraction to be
223 -- applied to the type of the local environment tuple
224 (Maybe Fixity) -- fixity (filled in by the renamer), for forms that
225 -- were converted from OpApp's by the renamer
226 [LHsCmdTop id] -- argument commands
229 ---------------------------------------
230 -- Haskell program coverage (Hpc) Support
233 Int -- module-local tick number
234 [id] -- variables in scope
235 (LHsExpr id) -- sub-expression
238 Int -- module-local tick number for True
239 Int -- module-local tick number for False
240 (LHsExpr id) -- sub-expression
242 | HsTickPragma -- A pragma introduced tick
243 (FastString,(Int,Int),(Int,Int)) -- external span for this tick
246 ---------------------------------------
247 -- These constructors only appear temporarily in the parser.
248 -- The renamer translates them into the Right Thing.
250 | EWildPat -- wildcard
252 | EAsPat (Located id) -- as pattern
255 | ELazyPat (LHsExpr id) -- ~ pattern
257 | HsType (LHsType id) -- Explicit type argument; e.g f {| Int |} x y
259 ---------------------------------------
260 -- Finally, HsWrap appears only in typechecker output
262 | HsWrap HsWrapper -- TRANSLATION
265 type PendingSplice = (Name, LHsExpr Id) -- Typechecked splices, waiting to be
266 -- pasted back in by the desugarer
269 A @Dictionary@, unless of length 0 or 1, becomes a tuple. A
270 @ClassDictLam dictvars methods expr@ is, therefore:
272 \ x -> case x of ( dictvars-and-methods-tuple ) -> expr
276 instance OutputableBndr id => Outputable (HsExpr id) where
277 ppr expr = pprExpr expr
281 -- pprExpr and pprLExpr call pprDeeper;
282 -- the underscore versions do not
283 pprExpr :: OutputableBndr id => HsExpr id -> SDoc
284 pprExpr e = pprDeeper (ppr_expr e)
286 pprLExpr :: OutputableBndr id => LHsExpr id -> SDoc
287 pprLExpr e = pprDeeper (ppr_expr (unLoc e))
289 pprBinds :: OutputableBndr id => HsLocalBinds id -> SDoc
290 pprBinds b = pprDeeper (ppr b)
292 ppr_lexpr :: OutputableBndr id => LHsExpr id -> SDoc
293 ppr_lexpr e = ppr_expr (unLoc e)
295 ppr_expr (HsVar v) = pprHsVar v
296 ppr_expr (HsIPVar v) = ppr v
297 ppr_expr (HsLit lit) = ppr lit
298 ppr_expr (HsOverLit lit) = ppr lit
299 ppr_expr (HsPar e) = parens (ppr_lexpr e)
301 ppr_expr (HsCoreAnn s e)
302 = vcat [ptext SLIT("HsCoreAnn") <+> ftext s, ppr_lexpr e]
304 ppr_expr (HsApp e1 e2)
305 = let (fun, args) = collect_args e1 [e2] in
306 hang (ppr_lexpr fun) 2 (sep (map pprParendExpr args))
308 collect_args (L _ (HsApp fun arg)) args = collect_args fun (arg:args)
309 collect_args fun args = (fun, args)
311 ppr_expr (OpApp e1 op fixity e2)
313 HsVar v -> pp_infixly v
316 pp_e1 = pprParendExpr e1 -- Add parens to make precedence clear
317 pp_e2 = pprParendExpr e2
320 = hang (ppr op) 2 (sep [pp_e1, pp_e2])
323 = sep [nest 2 pp_e1, pprInfix v, nest 2 pp_e2]
325 ppr_expr (NegApp e _) = char '-' <+> pprParendExpr e
327 ppr_expr (SectionL expr op)
329 HsVar v -> pp_infixly v
332 pp_expr = pprParendExpr expr
334 pp_prefixly = hang (hsep [text " \\ x_ ->", ppr op])
335 4 (hsep [pp_expr, ptext SLIT("x_ )")])
336 pp_infixly v = parens (sep [pp_expr, pprInfix v])
338 ppr_expr (SectionR op expr)
340 HsVar v -> pp_infixly v
343 pp_expr = pprParendExpr expr
345 pp_prefixly = hang (hsep [text "( \\ x_ ->", ppr op, ptext SLIT("x_")])
346 4 ((<>) pp_expr rparen)
348 = parens (sep [pprInfix v, pp_expr])
350 ppr_expr (HsLam matches)
351 = pprMatches LambdaExpr matches
353 ppr_expr (HsCase expr matches)
354 = sep [ sep [ptext SLIT("case"), nest 4 (ppr expr), ptext SLIT("of")],
355 nest 2 (pprMatches CaseAlt matches) ]
357 ppr_expr (HsIf e1 e2 e3)
358 = sep [hsep [ptext SLIT("if"), nest 2 (ppr e1), ptext SLIT("then")],
363 -- special case: let ... in let ...
364 ppr_expr (HsLet binds expr@(L _ (HsLet _ _)))
365 = sep [hang (ptext SLIT("let")) 2 (hsep [pprBinds binds, ptext SLIT("in")]),
368 ppr_expr (HsLet binds expr)
369 = sep [hang (ptext SLIT("let")) 2 (pprBinds binds),
370 hang (ptext SLIT("in")) 2 (ppr expr)]
372 ppr_expr (HsDo do_or_list_comp stmts body _) = pprDo do_or_list_comp stmts body
374 ppr_expr (ExplicitList _ exprs)
375 = brackets (pprDeeperList fsep (punctuate comma (map ppr_lexpr exprs)))
377 ppr_expr (ExplicitPArr _ exprs)
378 = pa_brackets (pprDeeperList fsep (punctuate comma (map ppr_lexpr exprs)))
380 ppr_expr (ExplicitTuple exprs boxity)
381 = tupleParens boxity (pprDeeperList sep (punctuate comma (map ppr_lexpr exprs)))
383 ppr_expr (RecordCon con_id con_expr rbinds)
384 = pp_rbinds (ppr con_id) rbinds
386 ppr_expr (RecordUpd aexp rbinds _ _ _)
387 = pp_rbinds (pprParendExpr aexp) rbinds
389 ppr_expr (ExprWithTySig expr sig)
390 = hang (nest 2 (ppr_lexpr expr) <+> dcolon)
392 ppr_expr (ExprWithTySigOut expr sig)
393 = hang (nest 2 (ppr_lexpr expr) <+> dcolon)
396 ppr_expr (ArithSeq expr info) = brackets (ppr info)
397 ppr_expr (PArrSeq expr info) = pa_brackets (ppr info)
399 ppr_expr EWildPat = char '_'
400 ppr_expr (ELazyPat e) = char '~' <> pprParendExpr e
401 ppr_expr (EAsPat v e) = ppr v <> char '@' <> pprParendExpr e
403 ppr_expr (HsSCC lbl expr)
404 = sep [ ptext SLIT("_scc_") <+> doubleQuotes (ftext lbl), pprParendExpr expr ]
406 ppr_expr (HsWrap co_fn e) = pprHsWrapper (ppr_expr e) co_fn
407 ppr_expr (HsType id) = ppr id
409 ppr_expr (HsSpliceE s) = pprSplice s
410 ppr_expr (HsBracket b) = pprHsBracket b
411 ppr_expr (HsBracketOut e []) = ppr e
412 ppr_expr (HsBracketOut e ps) = ppr e $$ ptext SLIT("pending") <+> ppr ps
414 ppr_expr (HsProc pat (L _ (HsCmdTop cmd _ _ _)))
415 = hsep [ptext SLIT("proc"), ppr pat, ptext SLIT("->"), ppr cmd]
417 ppr_expr (HsTick tickId vars exp)
418 = hcat [ptext SLIT("tick<"), ppr tickId,ptext SLIT(">("), hsep (map pprHsVar vars), ppr exp,ptext SLIT(")")]
419 ppr_expr (HsBinTick tickIdTrue tickIdFalse exp)
420 = hcat [ptext SLIT("bintick<"),
425 ppr exp,ptext SLIT(")")]
426 ppr_expr (HsTickPragma externalSrcLoc exp)
427 = hcat [ptext SLIT("tickpragma<"), ppr externalSrcLoc,ptext SLIT(">("), ppr exp,ptext SLIT(")")]
429 ppr_expr (HsArrApp arrow arg _ HsFirstOrderApp True)
430 = hsep [ppr_lexpr arrow, ptext SLIT("-<"), ppr_lexpr arg]
431 ppr_expr (HsArrApp arrow arg _ HsFirstOrderApp False)
432 = hsep [ppr_lexpr arg, ptext SLIT(">-"), ppr_lexpr arrow]
433 ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp True)
434 = hsep [ppr_lexpr arrow, ptext SLIT("-<<"), ppr_lexpr arg]
435 ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp False)
436 = hsep [ppr_lexpr arg, ptext SLIT(">>-"), ppr_lexpr arrow]
438 ppr_expr (HsArrForm (L _ (HsVar v)) (Just _) [arg1, arg2])
439 = sep [pprCmdArg (unLoc arg1), hsep [pprInfix v, pprCmdArg (unLoc arg2)]]
440 ppr_expr (HsArrForm op _ args)
441 = hang (ptext SLIT("(|") <> ppr_lexpr op)
442 4 (sep (map (pprCmdArg.unLoc) args) <> ptext SLIT("|)"))
444 pprCmdArg :: OutputableBndr id => HsCmdTop id -> SDoc
445 pprCmdArg (HsCmdTop cmd@(L _ (HsArrForm _ Nothing [])) _ _ _)
447 pprCmdArg (HsCmdTop cmd _ _ _)
448 = parens (ppr_lexpr cmd)
450 -- Put a var in backquotes if it's not an operator already
451 pprInfix :: Outputable name => name -> SDoc
452 pprInfix v | isOperator ppr_v = ppr_v
453 | otherwise = char '`' <> ppr_v <> char '`'
457 -- add parallel array brackets around a document
459 pa_brackets :: SDoc -> SDoc
460 pa_brackets p = ptext SLIT("[:") <> p <> ptext SLIT(":]")
463 Parenthesize unless very simple:
465 pprParendExpr :: OutputableBndr id => LHsExpr id -> SDoc
468 pp_as_was = pprLExpr expr
469 -- Using pprLExpr makes sure that we go 'deeper'
470 -- I think that is usually (always?) right
477 HsIPVar _ -> pp_as_was
478 ExplicitList _ _ -> pp_as_was
479 ExplicitPArr _ _ -> pp_as_was
480 ExplicitTuple _ _ -> pp_as_was
482 HsBracket _ -> pp_as_was
483 HsBracketOut _ [] -> pp_as_was
484 _ -> parens pp_as_was
487 %************************************************************************
489 \subsection{Commands (in arrow abstractions)}
491 %************************************************************************
493 We re-use HsExpr to represent these.
496 type HsCmd id = HsExpr id
498 type LHsCmd id = LHsExpr id
500 data HsArrAppType = HsHigherOrderApp | HsFirstOrderApp
503 The legal constructors for commands are:
505 = HsArrApp ... -- as above
507 | HsArrForm ... -- as above
512 | HsLam (Match id) -- kappa
514 -- the renamer turns this one into HsArrForm
515 | OpApp (HsExpr id) -- left operand
516 (HsCmd id) -- operator
517 Fixity -- Renamer adds fixity; bottom until then
518 (HsCmd id) -- right operand
520 | HsPar (HsCmd id) -- parenthesised command
523 [Match id] -- bodies are HsCmd's
526 | HsIf (HsExpr id) -- predicate
527 (HsCmd id) -- then part
528 (HsCmd id) -- else part
531 | HsLet (HsLocalBinds id) -- let(rec)
534 | HsDo (HsStmtContext Name) -- The parameterisation is unimportant
535 -- because in this context we never use
536 -- the PatGuard or ParStmt variant
537 [Stmt id] -- HsExpr's are really HsCmd's
538 PostTcType -- Type of the whole expression
541 Top-level command, introducing a new arrow.
542 This may occur inside a proc (where the stack is empty) or as an
543 argument of a command-forming operator.
546 type LHsCmdTop id = Located (HsCmdTop id)
549 = HsCmdTop (LHsCmd id)
550 [PostTcType] -- types of inputs on the command's stack
551 PostTcType -- return type of the command
553 -- after type checking:
554 -- names used in the command's desugaring
557 %************************************************************************
559 \subsection{Record binds}
561 %************************************************************************
564 data HsRecordBinds id = HsRecordBinds [(Located id, LHsExpr id)]
566 recBindFields :: HsRecordBinds id -> [id]
567 recBindFields (HsRecordBinds rbinds) = [unLoc field | (field,_) <- rbinds]
569 pp_rbinds :: OutputableBndr id => SDoc -> HsRecordBinds id -> SDoc
570 pp_rbinds thing (HsRecordBinds rbinds)
572 4 (braces (pprDeeperList sep (punctuate comma (map (pp_rbind) rbinds))))
574 pp_rbind (v, e) = hsep [pprBndr LetBind (unLoc v), char '=', ppr e]
579 %************************************************************************
581 \subsection{@Match@, @GRHSs@, and @GRHS@ datatypes}
583 %************************************************************************
585 @Match@es are sets of pattern bindings and right hand sides for
586 functions, patterns or case branches. For example, if a function @g@
592 then \tr{g} has two @Match@es: @(x,y) = y@ and @((x:ys),y) = y+1@.
594 It is always the case that each element of an @[Match]@ list has the
595 same number of @pats@s inside it. This corresponds to saying that
596 a function defined by pattern matching must have the same number of
597 patterns in each equation.
602 [LMatch id] -- The alternatives
603 PostTcType -- The type is the type of the entire group
604 -- t1 -> ... -> tn -> tr
605 -- where there are n patterns
607 type LMatch id = Located (Match id)
611 [LPat id] -- The patterns
612 (Maybe (LHsType id)) -- A type signature for the result of the match
613 -- Nothing after typechecking
616 matchGroupArity :: MatchGroup id -> Arity
617 matchGroupArity (MatchGroup [] _)
618 = panic "matchGroupArity" -- MatchGroup is never empty
619 matchGroupArity (MatchGroup (match:matches) _)
620 = ASSERT( all ((== n_pats) . length . hsLMatchPats) matches )
621 -- Assertion just checks that all the matches have the same number of pats
624 n_pats = length (hsLMatchPats match)
626 hsLMatchPats :: LMatch id -> [LPat id]
627 hsLMatchPats (L _ (Match pats _ _)) = pats
629 -- GRHSs are used both for pattern bindings and for Matches
631 = GRHSs [LGRHS id] -- Guarded RHSs
632 (HsLocalBinds id) -- The where clause
634 type LGRHS id = Located (GRHS id)
636 data GRHS id = GRHS [LStmt id] -- Guards
637 (LHsExpr id) -- Right hand side
640 We know the list must have at least one @Match@ in it.
643 pprMatches :: (OutputableBndr id) => HsMatchContext id -> MatchGroup id -> SDoc
644 pprMatches ctxt (MatchGroup matches ty) = vcat (map (pprMatch ctxt) (map unLoc matches))
645 -- Don't print the type; it's only
646 -- a place-holder before typechecking
648 -- Exported to HsBinds, which can't see the defn of HsMatchContext
649 pprFunBind :: (OutputableBndr id) => id -> MatchGroup id -> SDoc
650 pprFunBind fun matches = pprMatches (FunRhs fun) matches
652 -- Exported to HsBinds, which can't see the defn of HsMatchContext
653 pprPatBind :: (OutputableBndr bndr, OutputableBndr id)
654 => LPat bndr -> GRHSs id -> SDoc
655 pprPatBind pat grhss = sep [ppr pat, nest 4 (pprGRHSs PatBindRhs grhss)]
658 pprMatch :: OutputableBndr id => HsMatchContext id -> Match id -> SDoc
659 pprMatch ctxt (Match pats maybe_ty grhss)
660 = pp_name ctxt <+> sep [sep (map ppr pats),
662 nest 2 (pprGRHSs ctxt grhss)]
664 pp_name (FunRhs fun) = ppr fun -- Not pprBndr; the AbsBinds will
665 -- have printed the signature
666 pp_name LambdaExpr = char '\\'
667 pp_name other = empty
669 ppr_maybe_ty = case maybe_ty of
670 Just ty -> dcolon <+> ppr ty
674 pprGRHSs :: OutputableBndr id => HsMatchContext id -> GRHSs id -> SDoc
675 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 = ptext SLIT("do") <+> pprDeeperList vcat (map ppr stmts ++ [ppr body])
803 pprDo (MDoExpr _) stmts body = ptext SLIT("mdo") <+> pprDeeperList 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
806 pprDo other stmts body = panic "pprDo" -- PatGuard, ParStmtCxt
808 pprComp :: OutputableBndr id => (SDoc -> SDoc) -> [LStmt id] -> LHsExpr id -> SDoc
809 pprComp brack quals body
811 hang (ppr body <+> char '|')
815 %************************************************************************
817 Template Haskell quotation brackets
819 %************************************************************************
822 data HsSplice id = HsSplice -- $z or $(f 4)
823 id -- The id is just a unique name to
824 (LHsExpr id) -- identify this splice point
826 instance OutputableBndr id => Outputable (HsSplice id) where
829 pprSplice :: OutputableBndr id => HsSplice id -> SDoc
830 pprSplice (HsSplice n e) = char '$' <> brackets (ppr n) <> pprParendExpr e
833 data HsBracket id = ExpBr (LHsExpr id) -- [| expr |]
834 | PatBr (LPat id) -- [p| pat |]
835 | DecBr (HsGroup id) -- [d| decls |]
836 | TypBr (LHsType id) -- [t| type |]
837 | VarBr id -- 'x, ''T
839 instance OutputableBndr id => Outputable (HsBracket id) where
843 pprHsBracket (ExpBr e) = thBrackets empty (ppr e)
844 pprHsBracket (PatBr p) = thBrackets (char 'p') (ppr p)
845 pprHsBracket (DecBr d) = thBrackets (char 'd') (ppr d)
846 pprHsBracket (TypBr t) = thBrackets (char 't') (ppr t)
847 pprHsBracket (VarBr n) = char '\'' <> ppr n
848 -- Infelicity: can't show ' vs '', because
849 -- we can't ask n what its OccName is, because the
850 -- pretty-printer for HsExpr doesn't ask for NamedThings
851 -- But the pretty-printer for names will show the OccName class
853 thBrackets pp_kind pp_body = char '[' <> pp_kind <> char '|' <+>
854 pp_body <+> ptext SLIT("|]")
857 %************************************************************************
859 \subsection{Enumerations and list comprehensions}
861 %************************************************************************
866 | FromThen (LHsExpr id)
868 | FromTo (LHsExpr id)
870 | FromThenTo (LHsExpr id)
876 instance OutputableBndr id => Outputable (ArithSeqInfo id) where
877 ppr (From e1) = hcat [ppr e1, pp_dotdot]
878 ppr (FromThen e1 e2) = hcat [ppr e1, comma, space, ppr e2, pp_dotdot]
879 ppr (FromTo e1 e3) = hcat [ppr e1, pp_dotdot, ppr e3]
880 ppr (FromThenTo e1 e2 e3)
881 = hcat [ppr e1, comma, space, ppr e2, pp_dotdot, ppr e3]
883 pp_dotdot = ptext SLIT(" .. ")
887 %************************************************************************
889 \subsection{HsMatchCtxt}
891 %************************************************************************
894 data HsMatchContext id -- Context of a Match
895 = FunRhs id -- Function binding for f
896 | CaseAlt -- Guard on a case alternative
897 | LambdaExpr -- Pattern of a lambda
898 | ProcExpr -- Pattern of a proc
899 | PatBindRhs -- Pattern binding
900 | RecUpd -- Record update [used only in DsExpr to tell matchWrapper
901 -- what sort of runtime error message to generate]
902 | StmtCtxt (HsStmtContext id) -- Pattern of a do-stmt or list comprehension
905 data HsStmtContext id
908 | MDoExpr PostTcTable -- Recursive do-expression
909 -- (tiresomely, it needs table
910 -- of its return/bind ops)
911 | PArrComp -- Parallel array comprehension
912 | PatGuard (HsMatchContext id) -- Pattern guard for specified thing
913 | ParStmtCtxt (HsStmtContext id) -- A branch of a parallel stmt
917 isDoExpr :: HsStmtContext id -> Bool
918 isDoExpr DoExpr = True
919 isDoExpr (MDoExpr _) = True
920 isDoExpr other = False
924 matchSeparator (FunRhs _) = ptext SLIT("=")
925 matchSeparator CaseAlt = ptext SLIT("->")
926 matchSeparator LambdaExpr = ptext SLIT("->")
927 matchSeparator ProcExpr = ptext SLIT("->")
928 matchSeparator PatBindRhs = ptext SLIT("=")
929 matchSeparator (StmtCtxt _) = ptext SLIT("<-")
930 matchSeparator RecUpd = panic "unused"
934 pprMatchContext (FunRhs fun) = ptext SLIT("the definition of") <+> quotes (ppr fun)
935 pprMatchContext CaseAlt = ptext SLIT("a case alternative")
936 pprMatchContext RecUpd = ptext SLIT("a record-update construct")
937 pprMatchContext PatBindRhs = ptext SLIT("a pattern binding")
938 pprMatchContext LambdaExpr = ptext SLIT("a lambda abstraction")
939 pprMatchContext ProcExpr = ptext SLIT("an arrow abstraction")
940 pprMatchContext (StmtCtxt ctxt) = ptext SLIT("a pattern binding in") $$ pprStmtContext ctxt
942 pprStmtContext (ParStmtCtxt c) = sep [ptext SLIT("a parallel branch of"), pprStmtContext c]
943 pprStmtContext (PatGuard ctxt) = ptext SLIT("a pattern guard for") $$ pprMatchContext ctxt
944 pprStmtContext DoExpr = ptext SLIT("a 'do' expression")
945 pprStmtContext (MDoExpr _) = ptext SLIT("an 'mdo' expression")
946 pprStmtContext ListComp = ptext SLIT("a list comprehension")
947 pprStmtContext PArrComp = ptext SLIT("an array comprehension")
950 pprMatchRhsContext (FunRhs fun) = ptext SLIT("a right-hand side of function") <+> quotes (ppr fun)
951 pprMatchRhsContext CaseAlt = ptext SLIT("the body of a case alternative")
952 pprMatchRhsContext PatBindRhs = ptext SLIT("the right-hand side of a pattern binding")
953 pprMatchRhsContext LambdaExpr = ptext SLIT("the body of a lambda")
954 pprMatchRhsContext ProcExpr = ptext SLIT("the body of a proc")
955 pprMatchRhsContext other = panic "pprMatchRhsContext" -- RecUpd, StmtCtxt
957 -- Used for the result statement of comprehension
958 -- e.g. the 'e' in [ e | ... ]
959 -- or the 'r' in f x = r
960 pprStmtResultContext (PatGuard ctxt) = pprMatchRhsContext ctxt
961 pprStmtResultContext other = ptext SLIT("the result of") <+> pprStmtContext other
964 -- Used to generate the string for a *runtime* error message
965 matchContextErrString (FunRhs fun) = "function " ++ showSDoc (ppr fun)
966 matchContextErrString CaseAlt = "case"
967 matchContextErrString PatBindRhs = "pattern binding"
968 matchContextErrString RecUpd = "record update"
969 matchContextErrString LambdaExpr = "lambda"
970 matchContextErrString ProcExpr = "proc"
971 matchContextErrString (StmtCtxt (ParStmtCtxt c)) = matchContextErrString (StmtCtxt c)
972 matchContextErrString (StmtCtxt (PatGuard _)) = "pattern guard"
973 matchContextErrString (StmtCtxt DoExpr) = "'do' expression"
974 matchContextErrString (StmtCtxt (MDoExpr _)) = "'mdo' expression"
975 matchContextErrString (StmtCtxt ListComp) = "list comprehension"
976 matchContextErrString (StmtCtxt PArrComp) = "array comprehension"