2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[RnBinds]{Renaming and dependency analysis of bindings}
6 This module does renaming and dependency analysis on value bindings in
7 the abstract syntax. It does {\em not} do cycle-checks on class or
8 type-synonym declarations; those cannot be done at this stage because
9 they may be affected by renaming (which isn't fully worked out yet).
13 rnTopBinds, rnBinds, rnBindsAndThen,
14 rnMethodBinds, renameSigs, checkSigs
17 #include "HsVersions.h"
21 import HsBinds ( hsSigDoc, eqHsSig )
25 import RnTypes ( rnHsSigType, rnLHsType, rnLPat )
26 import RnExpr ( rnMatchGroup, rnMatch, rnGRHSs, checkPrecMatch )
27 import RnEnv ( bindLocatedLocalsRn, lookupLocatedBndrRn,
28 lookupLocatedInstDeclBndr,
29 lookupLocatedSigOccRn, bindPatSigTyVars, bindPatSigTyVarsFV,
31 warnUnusedLocalBinds, mapFvRn, extendTyVarEnvFVRn,
33 import CmdLineOpts ( DynFlag(..) )
34 import Digraph ( SCC(..), stronglyConnComp )
35 import Name ( Name, nameOccName, nameSrcLoc )
37 import PrelNames ( isUnboundName )
38 import RdrName ( RdrName, rdrNameOcc )
39 import BasicTypes ( RecFlag(..), TopLevelFlag(..), isTopLevel )
40 import List ( unzip4 )
41 import SrcLoc ( mkSrcSpan, Located(..), unLoc )
44 import Monad ( foldM )
47 -- ToDo: Put the annotations into the monad, so that they arrive in the proper
48 -- place and can be used when complaining.
50 The code tree received by the function @rnBinds@ contains definitions
51 in where-clauses which are all apparently mutually recursive, but which may
52 not really depend upon each other. For example, in the top level program
57 the definitions of @a@ and @y@ do not depend on each other at all.
58 Unfortunately, the typechecker cannot always check such definitions.
59 \footnote{Mycroft, A. 1984. Polymorphic type schemes and recursive
60 definitions. In Proceedings of the International Symposium on Programming,
61 Toulouse, pp. 217-39. LNCS 167. Springer Verlag.}
62 However, the typechecker usually can check definitions in which only the
63 strongly connected components have been collected into recursive bindings.
64 This is precisely what the function @rnBinds@ does.
66 ToDo: deal with case where a single monobinds binds the same variable
69 The vertag tag is a unique @Int@; the tags only need to be unique
70 within one @MonoBinds@, so that unique-Int plumbing is done explicitly
71 (heavy monad machinery not needed).
74 %************************************************************************
76 %* naming conventions *
78 %************************************************************************
80 \subsection[name-conventions]{Name conventions}
82 The basic algorithm involves walking over the tree and returning a tuple
83 containing the new tree plus its free variables. Some functions, such
84 as those walking polymorphic bindings (HsBinds) and qualifier lists in
85 list comprehensions (@Quals@), return the variables bound in local
86 environments. These are then used to calculate the free variables of the
87 expression evaluated in these environments.
89 Conventions for variable names are as follows:
92 new code is given a prime to distinguish it from the old.
95 a set of variables defined in @Exp@ is written @dvExp@
98 a set of variables free in @Exp@ is written @fvExp@
101 %************************************************************************
103 %* analysing polymorphic bindings (HsBindGroup, HsBind)
105 %************************************************************************
107 \subsubsection[dep-HsBinds]{Polymorphic bindings}
109 Non-recursive expressions are reconstructed without any changes at top
110 level, although their component expressions may have to be altered.
111 However, non-recursive expressions are currently not expected as
112 \Haskell{} programs, and this code should not be executed.
114 Monomorphic bindings contain information that is returned in a tuple
115 (a @FlatMonoBinds@) containing:
119 a unique @Int@ that serves as the ``vertex tag'' for this binding.
122 the name of a function or the names in a pattern. These are a set
123 referred to as @dvLhs@, the defined variables of the left hand side.
126 the free variables of the body. These are referred to as @fvBody@.
129 the definition's actual code. This is referred to as just @code@.
132 The function @nonRecDvFv@ returns two sets of variables. The first is
133 the set of variables defined in the set of monomorphic bindings, while the
134 second is the set of free variables in those bindings.
136 The set of variables defined in a non-recursive binding is just the
137 union of all of them, as @union@ removes duplicates. However, the
138 free variables in each successive set of cumulative bindings is the
139 union of those in the previous set plus those of the newest binding after
140 the defined variables of the previous set have been removed.
142 @rnMethodBinds@ deals only with the declarations in class and
143 instance declarations. It expects only to see @FunMonoBind@s, and
144 it expects the global environment to contain bindings for the binders
145 (which are all class operations).
147 %************************************************************************
149 \subsubsection{ Top-level bindings}
151 %************************************************************************
153 @rnTopMonoBinds@ assumes that the environment already
154 contains bindings for the binders of this particular binding.
157 rnTopBinds :: LHsBinds RdrName
159 -> RnM ([HsBindGroup Name], DefUses)
161 -- The binders of the binding are in scope already;
162 -- the top level scope resolution does that
164 rnTopBinds mbinds sigs
165 = bindPatSigTyVars (collectSigTysFromHsBinds (bagToList mbinds)) $ \ _ ->
166 -- Hmm; by analogy with Ids, this doesn't look right
167 -- Top-level bound type vars should really scope over
168 -- everything, but we only scope them over the other bindings
170 rnBinds TopLevel mbinds sigs
174 %************************************************************************
178 %************************************************************************
181 rnBindsAndThen :: Bag (LHsBind RdrName)
183 -> ([HsBindGroup Name] -> RnM (result, FreeVars))
184 -> RnM (result, FreeVars)
186 rnBindsAndThen mbinds sigs thing_inside
187 = -- Extract all the binders in this group, and extend the
188 -- current scope, inventing new names for the new binders
189 -- This also checks that the names form a set
190 bindLocatedLocalsRn doc mbinders_w_srclocs $ \ _ ->
191 bindPatSigTyVarsFV (collectSigTysFromHsBinds (bagToList mbinds)) $
193 -- Then install local fixity declarations
194 -- Notice that they scope over thing_inside too
195 bindLocalFixities [sig | L _ (FixSig sig) <- sigs ] $
198 rnBinds NotTopLevel mbinds sigs `thenM` \ (binds, bind_dus) ->
200 -- Now do the "thing inside"
201 thing_inside binds `thenM` \ (result,result_fvs) ->
203 -- Final error checking
205 all_uses = duUses bind_dus `plusFV` result_fvs
206 bndrs = duDefs bind_dus
207 unused_bndrs = nameSetToList (bndrs `minusNameSet` all_uses)
209 warnUnusedLocalBinds unused_bndrs `thenM_`
211 returnM (result, all_uses `minusNameSet` bndrs)
212 -- duUses: It's important to return all the uses, not the 'real uses' used for
213 -- warning about unused bindings. Otherwise consider:
215 -- y = let p = x in 'x' -- NB: p not used
216 -- If we don't "see" the dependency of 'y' on 'x', we may put the
217 -- bindings in the wrong order, and the type checker will complain
218 -- that x isn't in scope
220 mbinders_w_srclocs = collectHsBindLocatedBinders mbinds
221 doc = text "In the binding group for:"
222 <+> pprWithCommas ppr (map unLoc mbinders_w_srclocs)
226 %************************************************************************
228 \subsubsection{rnBinds -- the main work is done here}
230 %************************************************************************
232 @rnMonoBinds@ is used by {\em both} top-level and nested bindings.
233 It assumes that all variables bound in this group are already in scope.
234 This is done {\em either} by pass 3 (for the top-level bindings),
235 {\em or} by @rnMonoBinds@ (for the nested ones).
238 rnBinds :: TopLevelFlag
241 -> RnM ([HsBindGroup Name], DefUses)
243 -- Assumes the binders of the binding are in scope already
245 rnBinds top_lvl mbinds sigs
246 = renameSigs sigs `thenM` \ siglist ->
248 -- Rename the bindings, returning a [HsBindVertex]
249 -- which is a list of indivisible vertices so far as
250 -- the strongly-connected-components (SCC) analysis is concerned
251 mkBindVertices siglist mbinds `thenM` \ mbinds_info ->
253 -- Do the SCC analysis
255 scc_result = rnSCC mbinds_info
256 (groups, bind_dus_s) = unzip (map reconstructCycle scc_result)
257 bind_dus = mkDUs bind_dus_s
258 binders = duDefs bind_dus
260 -- Check for duplicate or mis-placed signatures
261 checkSigs (okBindSig binders) siglist `thenM_`
263 -- Warn about missing signatures,
264 -- but only at top level, and not in interface mode
265 -- (The latter is important when renaming bindings from 'deriving' clauses.)
266 doptM Opt_WarnMissingSigs `thenM` \ warn_missing_sigs ->
267 (if isTopLevel top_lvl &&
270 type_sig_vars = [ unLoc n | L _ (Sig n _) <- siglist]
271 un_sigd_binders = filter (not . (`elem` type_sig_vars))
272 (nameSetToList binders)
274 mappM_ missingSigWarn un_sigd_binders
279 returnM (groups, bind_dus `plusDU` usesOnly (hsSigsFVs siglist))
282 @mkBindVertices@ is ever-so-slightly magical in that it sticks
283 unique ``vertex tags'' on its output; minor plumbing required.
286 mkBindVertices :: [LSig Name] -- Signatures
289 mkBindVertices sigs = mapM (mkBindVertex sigs) . bagToList
291 mkBindVertex :: [LSig Name] -> LHsBind RdrName -> RnM BindVertex
292 mkBindVertex sigs (L loc (PatBind pat grhss ty))
294 rnLPat pat `thenM` \ (pat', pat_fvs) ->
296 -- Find which things are bound in this group
298 names_bound_here = mkNameSet (collectPatBinders pat')
300 sigsForMe names_bound_here sigs `thenM` \ sigs_for_me ->
301 rnGRHSs PatBindRhs grhss `thenM` \ (grhss', fvs) ->
303 (names_bound_here, fvs `plusFV` pat_fvs,
304 L loc (PatBind pat' grhss' ty), sigs_for_me
307 mkBindVertex sigs (L loc (FunBind name inf matches))
309 lookupLocatedBndrRn name `thenM` \ new_name ->
311 plain_name = unLoc new_name
312 names_bound_here = unitNameSet plain_name
314 sigsForMe names_bound_here sigs `thenM` \ sigs_for_me ->
315 rnMatchGroup (FunRhs plain_name) matches `thenM` \ (new_matches, fvs) ->
316 checkPrecMatch inf plain_name new_matches `thenM_`
318 (unitNameSet plain_name, fvs,
319 L loc (FunBind new_name inf new_matches), sigs_for_me
322 sigsForMe names_bound_here sigs
323 = foldlM check [] (filter (sigForThisGroup names_bound_here) sigs)
325 -- sigForThisGroup only returns signatures for
326 -- which sigName returns a Just
327 eq sig1 sig2 = eqHsSig (unLoc sig1) (unLoc sig2)
329 check sigs sig = case filter (eq sig) sigs of
330 [] -> returnM (sig:sigs)
331 other -> dupSigDeclErr sig other `thenM_`
336 @rnMethodBinds@ is used for the method bindings of a class and an instance
337 declaration. Like @rnBinds@ but without dependency analysis.
339 NOTA BENE: we record each {\em binder} of a method-bind group as a free variable.
340 That's crucial when dealing with an instance decl:
342 instance Foo (T a) where
345 This might be the {\em sole} occurrence of @op@ for an imported class @Foo@,
346 and unless @op@ occurs we won't treat the type signature of @op@ in the class
347 decl for @Foo@ as a source of instance-decl gates. But we should! Indeed,
348 in many ways the @op@ in an instance decl is just like an occurrence, not
352 rnMethodBinds :: Name -- Class name
353 -> [Name] -- Names for generic type variables
355 -> RnM (LHsBinds Name, FreeVars)
357 rnMethodBinds cls gen_tyvars binds
358 = foldM do_one (emptyBag,emptyFVs) (bagToList binds)
359 where do_one (binds,fvs) bind = do
360 (bind', fvs_bind) <- rnMethodBind cls gen_tyvars bind
361 return (bind' `unionBags` binds, fvs_bind `plusFV` fvs)
363 rnMethodBind cls gen_tyvars (L loc (FunBind name inf (MatchGroup matches _)))
365 lookupLocatedInstDeclBndr cls name `thenM` \ sel_name ->
366 let plain_name = unLoc sel_name in
367 -- We use the selector name as the binder
369 mapFvRn (rn_match plain_name) matches `thenM` \ (new_matches, fvs) ->
371 new_group = MatchGroup new_matches placeHolderType
373 checkPrecMatch inf plain_name new_group `thenM_`
374 returnM (unitBag (L loc (FunBind sel_name inf new_group)), fvs `addOneFV` plain_name)
376 -- Truly gruesome; bring into scope the correct members of the generic
377 -- type variables. See comments in RnSource.rnSourceDecl(ClassDecl)
378 rn_match sel_name match@(L _ (Match (L _ (TypePat ty) : _) _ _))
379 = extendTyVarEnvFVRn gen_tvs $
380 rnMatch (FunRhs sel_name) match
382 tvs = map (rdrNameOcc.unLoc) (extractHsTyRdrTyVars ty)
383 gen_tvs = [tv | tv <- gen_tyvars, nameOccName tv `elem` tvs]
385 rn_match sel_name match = rnMatch (FunRhs sel_name) match
388 -- Can't handle method pattern-bindings which bind multiple methods.
389 rnMethodBind cls gen_tyvars mbind@(L loc (PatBind other_pat _ _))
390 = addLocErr mbind methodBindErr `thenM_`
391 returnM (emptyBag, emptyFVs)
395 %************************************************************************
397 Strongly connected components
399 %************************************************************************
402 type BindVertex = (Defs, Uses, LHsBind Name, [LSig Name])
403 -- Signatures, if any, for this vertex
405 rnSCC :: [BindVertex] -> [SCC BindVertex]
406 rnSCC nodes = stronglyConnComp (mkEdges nodes)
410 mkEdges :: [BindVertex] -> [(BindVertex, VertexTag, [VertexTag])]
411 -- We keep the uses with the binding,
412 -- so we can track unused bindings better
414 = [ (thing, tag, dest_vertices uses)
415 | (thing@(_, uses, _, _), tag) <- tagged_nodes
418 tagged_nodes = nodes `zip` [0::VertexTag ..]
420 -- An edge (v,v') indicates that v depends on v'
421 dest_vertices uses = [ target_vertex
422 | ((defs, _, _, _), target_vertex) <- tagged_nodes,
423 defs `intersectsNameSet` uses
426 reconstructCycle :: SCC BindVertex -> (HsBindGroup Name, (Defs,Uses))
427 reconstructCycle (AcyclicSCC (defs, uses, bind, sigs))
428 = (HsBindGroup (unitBag bind) sigs NonRecursive, (defs, uses))
429 reconstructCycle (CyclicSCC cycle)
430 = (HsBindGroup this_gp_binds this_gp_sigs Recursive,
431 (unionManyNameSets defs_s, unionManyNameSets uses_s))
433 (defs_s, uses_s, binds_s, sigs_s) = unzip4 cycle
434 this_gp_binds = listToBag binds_s
435 this_gp_sigs = foldr1 (++) sigs_s
439 %************************************************************************
441 \subsubsection[dep-Sigs]{Signatures (and user-pragmas for values)}
443 %************************************************************************
445 @renameSigs@ checks for:
447 \item more than one sig for one thing;
448 \item signatures given for things not bound here;
449 \item with suitably flaggery, that all top-level things have type signatures.
452 At the moment we don't gather free-var info from the types in
453 signatures. We'd only need this if we wanted to report unused tyvars.
456 checkSigs :: (LSig Name -> Bool) -- OK-sig predicbate
459 checkSigs ok_sig sigs
460 -- Check for (a) duplicate signatures
461 -- (b) signatures for things not in this group
462 -- Well, I can't see the check for (a)... ToDo!
463 = mappM_ unknownSigErr (filter bad sigs)
465 bad sig = not (ok_sig sig) &&
467 Just n | isUnboundName n -> False
468 -- Don't complain about an unbound name again
471 -- We use lookupSigOccRn in the signatures, which is a little bit unsatisfactory
472 -- because this won't work for:
473 -- instance Foo T where
476 -- We'll just rename the INLINE prag to refer to whatever other 'op'
477 -- is in scope. (I'm assuming that Baz.op isn't in scope unqualified.)
478 -- Doesn't seem worth much trouble to sort this.
480 renameSigs :: [LSig RdrName] -> RnM [LSig Name]
481 renameSigs sigs = mappM (wrapLocM renameSig) (filter (not . isFixitySig . unLoc) sigs)
482 -- Remove fixity sigs which have been dealt with already
484 renameSig :: Sig RdrName -> RnM (Sig Name)
485 -- FixitSig is renamed elsewhere.
487 = lookupLocatedSigOccRn v `thenM` \ new_v ->
488 rnHsSigType (quotes (ppr v)) ty `thenM` \ new_ty ->
489 returnM (Sig new_v new_ty)
491 renameSig (SpecInstSig ty)
492 = rnLHsType (text "A SPECIALISE instance pragma") ty `thenM` \ new_ty ->
493 returnM (SpecInstSig new_ty)
495 renameSig (SpecSig v ty)
496 = lookupLocatedSigOccRn v `thenM` \ new_v ->
497 rnHsSigType (quotes (ppr v)) ty `thenM` \ new_ty ->
498 returnM (SpecSig new_v new_ty)
500 renameSig (InlineSig b v p)
501 = lookupLocatedSigOccRn v `thenM` \ new_v ->
502 returnM (InlineSig b new_v p)
506 %************************************************************************
508 \subsection{Error messages}
510 %************************************************************************
513 dupSigDeclErr (L loc sig) sigs
515 vcat [ptext SLIT("Duplicate") <+> what_it_is <> colon,
516 nest 2 (vcat (map ppr_sig (L loc sig:sigs)))]
518 what_it_is = hsSigDoc sig
519 ppr_sig (L loc sig) = ppr loc <> colon <+> ppr sig
521 unknownSigErr (L loc sig)
523 sep [ptext SLIT("Misplaced") <+> what_it_is <> colon, ppr sig]
525 what_it_is = hsSigDoc sig
528 = addWarnAt (mkSrcSpan loc loc) $
529 sep [ptext SLIT("Definition but no type signature for"), quotes (ppr var)]
531 loc = nameSrcLoc var -- TODO: make a proper span
534 = hang (ptext SLIT("Pattern bindings (except simple variables) not allowed in instance declarations"))