2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[HsExpr]{Abstract Haskell syntax: expressions}
9 #include "HsVersions.h"
12 import {-# SOURCE #-} HsMatches ( pprMatches, pprMatch, Match )
14 import HsBinds ( HsBinds(..) )
15 import HsBasic ( HsLit )
16 import BasicTypes ( Fixity(..), FixityDirection(..) )
17 import HsTypes ( HsType )
20 import Name ( Name, isLexId )
22 import PprType ( pprType, pprParendType )
24 import Var ( TyVar, Id )
25 import DataCon ( DataCon )
26 import SrcLoc ( SrcLoc )
29 %************************************************************************
31 \subsection{Expressions proper}
33 %************************************************************************
37 = HsVar id -- variable
38 | HsLit HsLit -- literal
39 | HsLitOut HsLit -- TRANSLATION
40 Type -- (with its type)
42 | HsLam (Match id pat) -- lambda
43 | HsApp (HsExpr id pat) -- application
46 -- Operator applications:
47 -- NB Bracketed ops such as (+) come out as Vars.
49 -- NB We need an expr for the operator in an OpApp/Section since
50 -- the typechecker may need to apply the operator to a few types.
52 | OpApp (HsExpr id pat) -- left operand
53 (HsExpr id pat) -- operator
54 Fixity -- Renamer adds fixity; bottom until then
55 (HsExpr id pat) -- right operand
57 -- We preserve prefix negation and parenthesis for the precedence parser.
58 -- They are eventually removed by the type checker.
60 | NegApp (HsExpr id pat) -- negated expr
61 (HsExpr id pat) -- the negate id (in a HsVar)
63 | HsPar (HsExpr id pat) -- parenthesised expr
65 | SectionL (HsExpr id pat) -- operand
66 (HsExpr id pat) -- operator
67 | SectionR (HsExpr id pat) -- operator
68 (HsExpr id pat) -- operand
70 | HsCase (HsExpr id pat)
74 | HsIf (HsExpr id pat) -- predicate
75 (HsExpr id pat) -- then part
76 (HsExpr id pat) -- else part
79 | HsLet (HsBinds id pat) -- let(rec)
83 [Stmt id pat] -- "do":one or more stmts
87 [Stmt id pat] -- "do":one or more stmts
91 Type -- Type of the whole expression
94 | ExplicitList -- syntactic list
96 | ExplicitListOut -- TRANSLATION
97 Type -- Gives type of components of list
100 | ExplicitTuple -- tuple
102 -- NB: Unit is ExplicitTuple []
103 -- for tuples, we can get the types
104 -- direct from the components
107 | HsCon DataCon -- TRANSLATION; a saturated constructor application
111 -- Record construction
112 | RecordCon id -- The constructor
113 (HsRecordBinds id pat)
115 | RecordConOut DataCon
116 (HsExpr id pat) -- Data con Id applied to type args
117 (HsRecordBinds id pat)
121 | RecordUpd (HsExpr id pat)
122 (HsRecordBinds id pat)
124 | RecordUpdOut (HsExpr id pat) -- TRANSLATION
125 Type -- Type of *result* record (may differ from
126 -- type of input record)
127 [id] -- Dicts needed for construction
128 (HsRecordBinds id pat)
130 | ExprWithTySig -- signature binding
133 | ArithSeqIn -- arithmetic sequence
134 (ArithSeqInfo id pat)
136 (HsExpr id pat) -- (typechecked, of course)
137 (ArithSeqInfo id pat)
139 | CCall FAST_STRING -- call into the C world; string is
140 [HsExpr id pat] -- the C function; exprs are the
141 -- arguments to pass.
142 Bool -- True <=> might cause Haskell
143 -- garbage-collection (must generate
144 -- more paranoid code)
145 Bool -- True <=> it's really a "casm"
146 -- NOTE: this CCall is the *boxed*
147 -- version; the desugarer will convert
148 -- it into the unboxed "ccall#".
149 Type -- The result type; will be *bottom*
150 -- until the typechecker gets ahold of it
152 | HsSCC FAST_STRING -- "set cost centre" (_scc_) annotation
153 (HsExpr id pat) -- expr whose cost is to be measured
156 These constructors only appear temporarily in the parser.
157 The renamer translates them into the Right Thing.
160 | EWildPat -- wildcard
162 | EAsPat id -- as pattern
165 | ELazyPat (HsExpr id pat) -- ~ pattern
168 Everything from here on appears only in typechecker output.
171 | TyLam -- TRANSLATION
174 | TyApp -- TRANSLATION
175 (HsExpr id pat) -- generated by Spec
178 -- DictLam and DictApp are "inverses"
186 type HsRecordBinds id pat
187 = [(id, HsExpr id pat, Bool)]
188 -- True <=> source code used "punning",
189 -- i.e. {op1, op2} rather than {op1=e1, op2=e2}
192 A @Dictionary@, unless of length 0 or 1, becomes a tuple. A
193 @ClassDictLam dictvars methods expr@ is, therefore:
195 \ x -> case x of ( dictvars-and-methods-tuple ) -> expr
199 instance (Outputable id, Outputable pat) =>
200 Outputable (HsExpr id pat) where
201 ppr expr = pprExpr expr
205 pprExpr :: (Outputable id, Outputable pat)
206 => HsExpr id pat -> SDoc
208 pprExpr e = pprDeeper (ppr_expr e)
209 pprBinds b = pprDeeper (ppr b)
211 ppr_expr (HsVar v) = ppr v
213 ppr_expr (HsLit lit) = ppr lit
214 ppr_expr (HsLitOut lit _) = ppr lit
216 ppr_expr (HsLam match)
217 = hsep [char '\\', nest 2 (pprMatch (True,empty) match)]
219 ppr_expr expr@(HsApp e1 e2)
220 = let (fun, args) = collect_args expr [] in
221 (ppr_expr fun) <+> (sep (map ppr_expr args))
223 collect_args (HsApp fun arg) args = collect_args fun (arg:args)
224 collect_args fun args = (fun, args)
226 ppr_expr (OpApp e1 op fixity e2)
228 HsVar v -> pp_infixly v
231 pp_e1 = pprParendExpr e1 -- Add parens to make precedence clear
232 pp_e2 = pprParendExpr e2
235 = hang (pprExpr op) 4 (sep [pp_e1, pp_e2])
238 = sep [pp_e1, hsep [pp_v_op, pp_e2]]
241 pp_v_op | isLexId (_PK_ (showSDoc pp_v)) = char '`' <> pp_v <> char '`'
243 -- Put it in backquotes if it's not an operator already
244 -- We use (showSDoc pp_v), rather than isSymOcc (getOccName v) simply so
245 -- that we don't need NamedThing in the context of all these funcions.
246 -- Gruesome, but simple.
248 ppr_expr (NegApp e _)
249 = char '-' <+> pprParendExpr e
251 ppr_expr (HsPar e) = parens (ppr_expr e)
253 ppr_expr (SectionL expr op)
255 HsVar v -> pp_infixly v
258 pp_expr = pprParendExpr expr
260 pp_prefixly = hang (hsep [text " \\ x_ ->", ppr op])
261 4 (hsep [pp_expr, ptext SLIT("x_ )")])
262 pp_infixly v = parens (sep [pp_expr, ppr v])
264 ppr_expr (SectionR op expr)
266 HsVar v -> pp_infixly v
269 pp_expr = pprParendExpr expr
271 pp_prefixly = hang (hsep [text "( \\ x_ ->", ppr op, ptext SLIT("x_")])
272 4 ((<>) pp_expr rparen)
274 = parens (sep [ppr v, pp_expr])
276 ppr_expr (HsCase expr matches _)
277 = sep [ sep [ptext SLIT("case"), nest 4 (pprExpr expr), ptext SLIT("of")],
278 nest 2 (pprMatches (True, empty) matches) ]
280 ppr_expr (HsIf e1 e2 e3 _)
281 = sep [hsep [ptext SLIT("if"), nest 2 (pprExpr e1), ptext SLIT("then")],
286 -- special case: let ... in let ...
287 ppr_expr (HsLet binds expr@(HsLet _ _))
288 = sep [hang (ptext SLIT("let")) 2 (hsep [pprBinds binds, ptext SLIT("in")]),
291 ppr_expr (HsLet binds expr)
292 = sep [hang (ptext SLIT("let")) 2 (pprBinds binds),
293 hang (ptext SLIT("in")) 2 (ppr expr)]
295 ppr_expr (HsDo do_or_list_comp stmts _) = pprDo do_or_list_comp stmts
296 ppr_expr (HsDoOut do_or_list_comp stmts _ _ _ _ _) = pprDo do_or_list_comp stmts
298 ppr_expr (ExplicitList exprs)
299 = brackets (fsep (punctuate comma (map ppr_expr exprs)))
300 ppr_expr (ExplicitListOut ty exprs)
301 = hcat [ brackets (fsep (punctuate comma (map ppr_expr exprs))),
302 ifNotPprForUser ((<>) space (parens (pprType ty))) ]
304 ppr_expr (ExplicitTuple exprs True)
305 = parens (sep (punctuate comma (map ppr_expr exprs)))
307 ppr_expr (ExplicitTuple exprs False)
308 = ptext SLIT("(#") <> sep (punctuate comma (map ppr_expr exprs)) <> ptext SLIT("#)")
310 ppr_expr (HsCon con_id tys args)
311 = ppr con_id <+> sep (map pprParendType tys ++
312 map pprParendExpr args)
314 ppr_expr (RecordCon con_id rbinds)
315 = pp_rbinds (ppr con_id) rbinds
316 ppr_expr (RecordConOut data_con con rbinds)
317 = pp_rbinds (ppr con) rbinds
319 ppr_expr (RecordUpd aexp rbinds)
320 = pp_rbinds (pprParendExpr aexp) rbinds
321 ppr_expr (RecordUpdOut aexp _ _ rbinds)
322 = pp_rbinds (pprParendExpr aexp) rbinds
324 ppr_expr (ExprWithTySig expr sig)
325 = hang (nest 2 (ppr_expr expr) <+> dcolon)
328 ppr_expr (ArithSeqIn info)
329 = brackets (ppr info)
330 ppr_expr (ArithSeqOut expr info)
331 = brackets (ppr info)
333 ppr_expr EWildPat = char '_'
334 ppr_expr (ELazyPat e) = char '~' <> pprParendExpr e
335 ppr_expr (EAsPat v e) = ppr v <> char '@' <> pprParendExpr e
337 ppr_expr (CCall fun args _ is_asm result_ty)
339 then ptext SLIT("_casm_ ``") <> ptext fun <> ptext SLIT("''")
340 else ptext SLIT("_ccall_") <+> ptext fun)
341 4 (sep (map pprParendExpr args))
343 ppr_expr (HsSCC lbl expr)
344 = sep [ ptext SLIT("_scc_") <+> doubleQuotes (ptext lbl), pprParendExpr expr ]
346 ppr_expr (TyLam tyvars expr)
347 = hang (hsep [ptext SLIT("/\\"), interppSP tyvars, ptext SLIT("->")])
350 ppr_expr (TyApp expr [ty])
351 = hang (ppr_expr expr) 4 (pprParendType ty)
353 ppr_expr (TyApp expr tys)
354 = hang (ppr_expr expr)
355 4 (brackets (interpp'SP tys))
357 ppr_expr (DictLam dictvars expr)
358 = hang (hsep [ptext SLIT("\\{-dict-}"), interppSP dictvars, ptext SLIT("->")])
361 ppr_expr (DictApp expr [dname])
362 = hang (ppr_expr expr) 4 (ppr dname)
364 ppr_expr (DictApp expr dnames)
365 = hang (ppr_expr expr)
366 4 (brackets (interpp'SP dnames))
370 Parenthesize unless very simple:
372 pprParendExpr :: (Outputable id, Outputable pat)
373 => HsExpr id pat -> SDoc
377 pp_as_was = pprExpr expr
381 HsLitOut l _ -> ppr l
384 ExplicitList _ -> pp_as_was
385 ExplicitListOut _ _ -> pp_as_was
386 ExplicitTuple _ _ -> pp_as_was
389 _ -> parens pp_as_was
392 %************************************************************************
394 \subsection{Record binds}
396 %************************************************************************
399 pp_rbinds :: (Outputable id, Outputable pat)
401 -> HsRecordBinds id pat -> SDoc
403 pp_rbinds thing rbinds
405 4 (braces (hsep (punctuate comma (map (pp_rbind) rbinds))))
407 pp_rbind (v, e, pun_flag)
408 = getPprStyle $ \ sty ->
409 if pun_flag && userStyle sty then
412 hsep [ppr v, char '=', ppr e]
415 %************************************************************************
417 \subsection{Do stmts and list comprehensions}
419 %************************************************************************
422 data StmtCtxt -- Context of a Stmt
423 = DoStmt -- Do Statment
424 | ListComp -- List comprehension
425 | CaseAlt -- Guard on a case alternative
426 | PatBindRhs -- Guard on a pattern binding
427 | FunRhs Name -- Guard on a function defn for f
428 | LambdaBody -- Body of a lambda abstraction
431 = hang (ptext SLIT("do")) 2 (vcat (map ppr stmts))
434 hang (pprExpr expr <+> char '|')
437 ReturnStmt expr = last stmts -- Last stmt should be a ReturnStmt for list comps
447 | LetStmt (HsBinds id pat)
449 | GuardStmt (HsExpr id pat) -- List comps only
452 | ExprStmt (HsExpr id pat) -- Do stmts; and guarded things at the end
455 | ReturnStmt (HsExpr id pat) -- List comps only, at the end
459 instance (Outputable id, Outputable pat) =>
460 Outputable (Stmt id pat) where
461 ppr stmt = pprStmt stmt
463 pprStmt (BindStmt pat expr _)
464 = hsep [ppr pat, ptext SLIT("<-"), ppr expr]
465 pprStmt (LetStmt binds)
466 = hsep [ptext SLIT("let"), pprBinds binds]
467 pprStmt (ExprStmt expr _)
469 pprStmt (GuardStmt expr _)
471 pprStmt (ReturnStmt expr)
472 = hsep [ptext SLIT("return"), ppr expr]
475 %************************************************************************
477 \subsection{Enumerations and list comprehensions}
479 %************************************************************************
482 data ArithSeqInfo id pat
483 = From (HsExpr id pat)
484 | FromThen (HsExpr id pat)
486 | FromTo (HsExpr id pat)
488 | FromThenTo (HsExpr id pat)
494 instance (Outputable id, Outputable pat) =>
495 Outputable (ArithSeqInfo id pat) where
496 ppr (From e1) = hcat [ppr e1, pp_dotdot]
497 ppr (FromThen e1 e2) = hcat [ppr e1, comma, space, ppr e2, pp_dotdot]
498 ppr (FromTo e1 e3) = hcat [ppr e1, pp_dotdot, ppr e3]
499 ppr (FromThenTo e1 e2 e3)
500 = hcat [ppr e1, comma, space, ppr e2, pp_dotdot, ppr e3]
502 pp_dotdot = ptext SLIT(" .. ")