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 HsLit ( HsLit, HsOverLit )
16 import BasicTypes ( Fixity(..) )
17 import HsTypes ( HsType )
20 import Name ( Name, isLexSym )
22 import PprType ( pprType, pprParendType )
25 import DataCon ( DataCon )
26 import CStrings ( CLabelString, pprCLabelString )
27 import BasicTypes ( Boxity, tupleParens )
28 import SrcLoc ( SrcLoc )
31 %************************************************************************
33 \subsection{Expressions proper}
35 %************************************************************************
39 = HsVar id -- variable
40 | HsIPVar id -- implicit parameter
41 | HsOverLit (HsOverLit id) -- Overloaded literals; eliminated by type checker
42 | HsLit HsLit -- Simple (non-overloaded) literals
44 | HsLam (Match id pat) -- lambda
45 | HsApp (HsExpr id pat) -- application
48 -- Operator applications:
49 -- NB Bracketed ops such as (+) come out as Vars.
51 -- NB We need an expr for the operator in an OpApp/Section since
52 -- the typechecker may need to apply the operator to a few types.
54 | OpApp (HsExpr id pat) -- left operand
55 (HsExpr id pat) -- operator
56 Fixity -- Renamer adds fixity; bottom until then
57 (HsExpr id pat) -- right operand
59 -- We preserve prefix negation and parenthesis for the precedence parser.
60 -- They are eventually removed by the type checker.
62 | NegApp (HsExpr id pat) -- negated expr
63 id -- the negate id (in a HsVar)
65 | HsPar (HsExpr id pat) -- parenthesised expr
67 | SectionL (HsExpr id pat) -- operand
68 (HsExpr id pat) -- operator
69 | SectionR (HsExpr id pat) -- operator
70 (HsExpr id pat) -- operand
72 | HsCase (HsExpr id pat)
76 | HsIf (HsExpr id pat) -- predicate
77 (HsExpr id pat) -- then part
78 (HsExpr id pat) -- else part
81 | HsLet (HsBinds id pat) -- let(rec)
84 | HsWith (HsExpr id pat) -- implicit parameter binding
88 [Stmt id pat] -- "do":one or more stmts
92 [Stmt id pat] -- "do":one or more stmts
96 Type -- Type of the whole expression
99 | ExplicitList -- syntactic list
101 | ExplicitListOut -- TRANSLATION
102 Type -- Gives type of components of list
105 | ExplicitTuple -- tuple
107 -- NB: Unit is ExplicitTuple []
108 -- for tuples, we can get the types
109 -- direct from the components
113 -- Record construction
114 | RecordCon id -- The constructor
115 (HsRecordBinds id pat)
117 | RecordConOut DataCon
118 (HsExpr id pat) -- Data con Id applied to type args
119 (HsRecordBinds id pat)
123 | RecordUpd (HsExpr id pat)
124 (HsRecordBinds id pat)
126 | RecordUpdOut (HsExpr id pat) -- TRANSLATION
127 Type -- Type of *result* record (may differ from
128 -- type of input record)
129 [id] -- Dicts needed for construction
130 (HsRecordBinds id pat)
132 | ExprWithTySig -- signature binding
135 | ArithSeqIn -- arithmetic sequence
136 (ArithSeqInfo id pat)
138 (HsExpr id pat) -- (typechecked, of course)
139 (ArithSeqInfo id pat)
141 | HsCCall CLabelString -- call into the C world; string is
142 [HsExpr id pat] -- the C function; exprs are the
143 -- arguments to pass.
144 Bool -- True <=> might cause Haskell
145 -- garbage-collection (must generate
146 -- more paranoid code)
147 Bool -- True <=> it's really a "casm"
148 -- NOTE: this CCall is the *boxed*
149 -- version; the desugarer will convert
150 -- it into the unboxed "ccall#".
151 Type -- The result type; will be *bottom*
152 -- until the typechecker gets ahold of it
154 | HsSCC FAST_STRING -- "set cost centre" (_scc_) annotation
155 (HsExpr id pat) -- expr whose cost is to be measured
158 These constructors only appear temporarily in the parser.
159 The renamer translates them into the Right Thing.
162 | EWildPat -- wildcard
164 | EAsPat id -- as pattern
167 | ELazyPat (HsExpr id pat) -- ~ pattern
170 Everything from here on appears only in typechecker output.
173 | TyLam -- TRANSLATION
176 | TyApp -- TRANSLATION
177 (HsExpr id pat) -- generated by Spec
180 -- DictLam and DictApp are "inverses"
188 type HsRecordBinds id pat
189 = [(id, HsExpr id pat, Bool)]
190 -- True <=> source code used "punning",
191 -- i.e. {op1, op2} rather than {op1=e1, op2=e2}
194 A @Dictionary@, unless of length 0 or 1, becomes a tuple. A
195 @ClassDictLam dictvars methods expr@ is, therefore:
197 \ x -> case x of ( dictvars-and-methods-tuple ) -> expr
201 instance (Outputable id, Outputable pat) =>
202 Outputable (HsExpr id pat) where
203 ppr expr = pprExpr expr
207 pprExpr :: (Outputable id, Outputable pat)
208 => HsExpr id pat -> SDoc
210 pprExpr e = pprDeeper (ppr_expr e)
211 pprBinds b = pprDeeper (ppr b)
214 -- Put it in parens if it's an operator
215 | isOperator v = parens (ppr v)
218 ppr_expr (HsIPVar v) = {- char '?' <> -} ppr v
219 ppr_expr (HsLit lit) = ppr lit
220 ppr_expr (HsOverLit lit) = ppr lit
222 ppr_expr (HsLam match)
223 = hsep [char '\\', nest 2 (pprMatch (True,empty) match)]
225 ppr_expr expr@(HsApp e1 e2)
226 = let (fun, args) = collect_args expr [] in
227 (ppr_expr fun) <+> (sep (map ppr_expr args))
229 collect_args (HsApp fun arg) args = collect_args fun (arg:args)
230 collect_args fun args = (fun, args)
232 ppr_expr (OpApp e1 op fixity e2)
234 HsVar v -> pp_infixly v
237 pp_e1 = pprParendExpr e1 -- Add parens to make precedence clear
238 pp_e2 = pprParendExpr e2
241 = hang (pprExpr op) 4 (sep [pp_e1, pp_e2])
244 = sep [pp_e1, hsep [pp_v_op, pp_e2]]
246 pp_v_op | isOperator v = ppr v
247 | otherwise = char '`' <> ppr v <> char '`'
248 -- Put it in backquotes if it's not an operator already
250 ppr_expr (NegApp e _) = char '-' <+> pprParendExpr e
252 ppr_expr (HsPar e) = parens (ppr_expr e)
254 ppr_expr (SectionL expr op)
256 HsVar v -> pp_infixly v
259 pp_expr = pprParendExpr expr
261 pp_prefixly = hang (hsep [text " \\ x_ ->", ppr op])
262 4 (hsep [pp_expr, ptext SLIT("x_ )")])
263 pp_infixly v = parens (sep [pp_expr, ppr v])
265 ppr_expr (SectionR op expr)
267 HsVar v -> pp_infixly v
270 pp_expr = pprParendExpr expr
272 pp_prefixly = hang (hsep [text "( \\ x_ ->", ppr op, ptext SLIT("x_")])
273 4 ((<>) pp_expr rparen)
275 = parens (sep [ppr v, pp_expr])
277 ppr_expr (HsCase expr matches _)
278 = sep [ sep [ptext SLIT("case"), nest 4 (pprExpr expr), ptext SLIT("of")],
279 nest 2 (pprMatches (True, empty) matches) ]
281 ppr_expr (HsIf e1 e2 e3 _)
282 = sep [hsep [ptext SLIT("if"), nest 2 (pprExpr e1), ptext SLIT("then")],
287 -- special case: let ... in let ...
288 ppr_expr (HsLet binds expr@(HsLet _ _))
289 = sep [hang (ptext SLIT("let")) 2 (hsep [pprBinds binds, ptext SLIT("in")]),
292 ppr_expr (HsLet binds expr)
293 = sep [hang (ptext SLIT("let")) 2 (pprBinds binds),
294 hang (ptext SLIT("in")) 2 (ppr expr)]
296 ppr_expr (HsWith expr binds)
297 = hsep [ppr expr, ptext SLIT("with"), ppr binds]
299 ppr_expr (HsDo do_or_list_comp stmts _) = pprDo do_or_list_comp stmts
300 ppr_expr (HsDoOut do_or_list_comp stmts _ _ _ _ _) = pprDo do_or_list_comp stmts
302 ppr_expr (ExplicitList exprs)
303 = brackets (fsep (punctuate comma (map ppr_expr exprs)))
304 ppr_expr (ExplicitListOut ty exprs)
305 = hcat [ brackets (fsep (punctuate comma (map ppr_expr exprs))),
306 ifNotPprForUser ((<>) space (parens (pprType ty))) ]
308 ppr_expr (ExplicitTuple exprs boxity)
309 = tupleParens boxity (sep (punctuate comma (map ppr_expr exprs)))
311 ppr_expr (RecordCon con_id rbinds)
312 = pp_rbinds (ppr con_id) rbinds
313 ppr_expr (RecordConOut data_con con rbinds)
314 = pp_rbinds (ppr con) rbinds
316 ppr_expr (RecordUpd aexp rbinds)
317 = pp_rbinds (pprParendExpr aexp) rbinds
318 ppr_expr (RecordUpdOut aexp _ _ rbinds)
319 = pp_rbinds (pprParendExpr aexp) rbinds
321 ppr_expr (ExprWithTySig expr sig)
322 = hang (nest 2 (ppr_expr expr) <+> dcolon)
325 ppr_expr (ArithSeqIn info)
326 = brackets (ppr info)
327 ppr_expr (ArithSeqOut expr info)
328 = brackets (ppr info)
330 ppr_expr EWildPat = char '_'
331 ppr_expr (ELazyPat e) = char '~' <> pprParendExpr e
332 ppr_expr (EAsPat v e) = ppr v <> char '@' <> pprParendExpr e
334 ppr_expr (HsCCall fun args _ is_asm result_ty)
336 then ptext SLIT("_casm_ ``") <> pprCLabelString fun <> ptext SLIT("''")
337 else ptext SLIT("_ccall_") <+> pprCLabelString fun)
338 4 (sep (map pprParendExpr args))
340 ppr_expr (HsSCC lbl expr)
341 = sep [ ptext SLIT("_scc_") <+> doubleQuotes (ptext lbl), pprParendExpr expr ]
343 ppr_expr (TyLam tyvars expr)
344 = hang (hsep [ptext SLIT("/\\"), interppSP tyvars, ptext SLIT("->")])
347 ppr_expr (TyApp expr [ty])
348 = hang (ppr_expr expr) 4 (pprParendType ty)
350 ppr_expr (TyApp expr tys)
351 = hang (ppr_expr expr)
352 4 (brackets (interpp'SP tys))
354 ppr_expr (DictLam dictvars expr)
355 = hang (hsep [ptext SLIT("\\{-dict-}"), interppSP dictvars, ptext SLIT("->")])
358 ppr_expr (DictApp expr [dname])
359 = hang (ppr_expr expr) 4 (ppr dname)
361 ppr_expr (DictApp expr dnames)
362 = hang (ppr_expr expr)
363 4 (brackets (interpp'SP dnames))
367 Parenthesize unless very simple:
369 pprParendExpr :: (Outputable id, Outputable pat)
370 => HsExpr id pat -> SDoc
374 pp_as_was = pprExpr expr
381 HsIPVar _ -> pp_as_was
382 ExplicitList _ -> pp_as_was
383 ExplicitListOut _ _ -> pp_as_was
384 ExplicitTuple _ _ -> pp_as_was
387 _ -> parens pp_as_was
391 isOperator :: Outputable a => a -> Bool
392 isOperator v = isLexSym (_PK_ (showSDoc (ppr v)))
393 -- We use (showSDoc (ppr v)), rather than isSymOcc (getOccName v) simply so
394 -- that we don't need NamedThing in the context of all these functions.
395 -- Gruesome, but simple.
398 %************************************************************************
400 \subsection{Record binds}
402 %************************************************************************
405 pp_rbinds :: (Outputable id, Outputable pat)
407 -> HsRecordBinds id pat -> SDoc
409 pp_rbinds thing rbinds
411 4 (braces (sep (punctuate comma (map (pp_rbind) rbinds))))
413 pp_rbind (v, e, pun_flag)
414 = getPprStyle $ \ sty ->
415 if pun_flag && userStyle sty then
418 hsep [ppr v, char '=', ppr e]
421 %************************************************************************
423 \subsection{Do stmts and list comprehensions}
425 %************************************************************************
428 data StmtCtxt -- Context of a Stmt
429 = DoStmt -- Do Statment
430 | ListComp -- List comprehension
431 | CaseAlt -- Guard on a case alternative
432 | PatBindRhs -- Guard on a pattern binding
433 | FunRhs Name -- Guard on a function defn for f
434 | LambdaBody -- Body of a lambda abstraction
437 = hang (ptext SLIT("do")) 2 (vcat (map ppr stmts))
440 hang (pprExpr expr <+> char '|')
443 ReturnStmt expr = last stmts -- Last stmt should be a ReturnStmt for list comps
453 | LetStmt (HsBinds id pat)
455 | GuardStmt (HsExpr id pat) -- List comps only
458 | ExprStmt (HsExpr id pat) -- Do stmts; and guarded things at the end
461 | ReturnStmt (HsExpr id pat) -- List comps only, at the end
463 consLetStmt :: HsBinds id pat -> [Stmt id pat] -> [Stmt id pat]
464 consLetStmt EmptyBinds stmts = stmts
465 consLetStmt binds stmts = LetStmt binds : stmts
469 instance (Outputable id, Outputable pat) =>
470 Outputable (Stmt id pat) where
471 ppr stmt = pprStmt stmt
473 pprStmt (BindStmt pat expr _)
474 = hsep [ppr pat, ptext SLIT("<-"), ppr expr]
475 pprStmt (LetStmt binds)
476 = hsep [ptext SLIT("let"), pprBinds binds]
477 pprStmt (ExprStmt expr _)
479 pprStmt (GuardStmt expr _)
481 pprStmt (ReturnStmt expr)
482 = hsep [ptext SLIT("return"), ppr expr]
485 %************************************************************************
487 \subsection{Enumerations and list comprehensions}
489 %************************************************************************
492 data ArithSeqInfo id pat
493 = From (HsExpr id pat)
494 | FromThen (HsExpr id pat)
496 | FromTo (HsExpr id pat)
498 | FromThenTo (HsExpr id pat)
504 instance (Outputable id, Outputable pat) =>
505 Outputable (ArithSeqInfo id pat) where
506 ppr (From e1) = hcat [ppr e1, pp_dotdot]
507 ppr (FromThen e1 e2) = hcat [ppr e1, comma, space, ppr e2, pp_dotdot]
508 ppr (FromTo e1 e3) = hcat [ppr e1, pp_dotdot, ppr e3]
509 ppr (FromThenTo e1 e2 e3)
510 = hcat [ppr e1, comma, space, ppr e2, pp_dotdot, ppr e3]
512 pp_dotdot = ptext SLIT(" .. ")