diff --git a/ghc/compiler/deSugar/Match.lhs b/ghc/compiler/deSugar/Match.lhs
index a0cdb445a4e00b41d310972042cb2587f9b7623c..ed56ab7781f7ebba151efc66dc7332e1b72492c2 100644
--- a/ghc/compiler/deSugar/Match.lhs
+++ b/ghc/compiler/deSugar/Match.lhs
@@ -1,3 +1,4 @@
+
%
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
%
@@ -6,7 +7,7 @@
\begin{code}
#include "HsVersions.h"
-module Match ( match, matchWrapper, matchSimply ) where
+module Match ( matchExport, match, matchWrapper, matchSimply ) where
IMP_Ubiq()
#if defined(__GLASGOW_HASKELL__) && __GLASGOW_HASKELL__ <= 201
@@ -17,30 +18,33 @@ import {-# SOURCE #-} DsExpr ( dsExpr )
import {-# SOURCE #-} DsBinds ( dsBinds )
#endif
-import CmdLineOpts ( opt_WarnIncompletePatterns, opt_WarnOverlappedPatterns )
+import CmdLineOpts ( opt_WarnIncompletePatterns, opt_WarnOverlappedPatterns,
+ opt_PprUserLength,opt_WarnSimplePatterns
+ )
import HsSyn
import TcHsSyn ( SYN_IE(TypecheckedPat), SYN_IE(TypecheckedMatch),
SYN_IE(TypecheckedHsBinds), SYN_IE(TypecheckedHsExpr) )
import DsHsSyn ( outPatType, collectTypedPatBinders )
+import Check ( check, SYN_IE(ExhaustivePat), SYN_IE(WarningPat), BoxedString )
import CoreSyn
-
import CoreUtils ( coreExprType )
import DsMonad
import DsGRHSs ( dsGRHSs )
import DsUtils
-import MatchCon ( matchConFamily )
-import MatchLit ( matchLiterals )
-
+import ErrUtils ( SYN_IE(Warning) )
import FieldLabel ( FieldLabel {- Eq instance -} )
import Id ( idType, dataConFieldLabels,
dataConArgTys, recordSelectorFieldLabel,
GenId{-instance-}, SYN_IE(Id)
)
+import MatchCon ( matchConFamily )
+import MatchLit ( matchLiterals )
import Name ( Name {--O only-} )
-import Outputable ( PprStyle(..), Outputable(..) )
+import Outputable ( PprStyle(..), Outputable(..), pprQuote )
import PprType ( GenType{-instance-}, GenTyVar{-ditto-} )
-import Pretty ( Doc )
+import Pretty
import PrelVals ( pAT_ERROR_ID )
+import SrcLoc ( noSrcLoc, SrcLoc )
import Type ( isPrimType, eqTy, getAppDataTyConExpandingDicts,
instantiateTauTy, SYN_IE(Type)
)
@@ -55,9 +59,140 @@ import TysWiredIn ( nilDataCon, consDataCon, mkTupleTy, mkListTy,
addrDataCon, wordTy, wordDataCon
)
import Unique ( Unique{-instance Eq-} )
+import UniqSet
import Util ( panic, pprPanic, assertPanic )
\end{code}
+This function is a wrapper of @match@, it must be called from all the parts where
+it was called match, but only substitutes the firs call, ....
+if the associated flags are declared, warnings will be issued.
+It can not be called matchWrapper because this name already exists :-(
+
+JJCQ 30-Nov-1997
+
+\begin{code}
+matchExport :: [Id] -- Vars rep'ing the exprs we're matching with
+ -> [EquationInfo] -- Info about patterns, etc. (type synonym below)
+ -> DsM MatchResult -- Desugared result!
+
+matchExport vars qs@((EqnInfo _ ctx _ (MatchResult _ _ _)) : _)
+ | incomplete && shadow =
+ dsShadowWarn ctx eqns_shadow `thenDs` \ () ->
+ dsIncompleteWarn ctx pats `thenDs` \ () ->
+ match vars qs
+ | incomplete =
+ dsIncompleteWarn ctx pats `thenDs` \ () ->
+ match vars qs
+ | shadow =
+ dsShadowWarn ctx eqns_shadow `thenDs` \ () ->
+ match vars qs
+ | otherwise =
+ match vars qs
+ where (pats,indexs) = check qs
+ incomplete = opt_WarnIncompletePatterns && (length pats /= 0)
+ shadow = opt_WarnOverlappedPatterns && sizeUniqSet indexs < no_eqns
+ no_eqns = length qs
+ unused_eqns = uniqSetToList (mkUniqSet [1..no_eqns] `minusUniqSet` indexs)
+ eqns_shadow = map (\n -> qs!!(n - 1)) unused_eqns
+\end{code}
+
+This variable shows the maximun number of lines of output generated for warnings.
+It will limit the number of patterns/equations displayed to maximum_output.
+
+\begin{code}
+maximum_output = 4
+\end{code}
+
+The next two functions creates the warning message.
+
+\begin{code}
+dsShadowWarn :: DsMatchContext -> [EquationInfo] -> DsM ()
+dsShadowWarn ctx@(DsMatchContext kind _ _) qs = dsWarn warn
+ where
+ warn sty | length qs > maximum_output =
+ hang (pp_context sty ctx (ptext SLIT("are overlapped")))
+ 12 ((vcat $ map (ppr_eqn kind sty) (take maximum_output qs))
+ $$ ptext SLIT("..."))
+ warn sty =
+ hang (pp_context sty ctx (ptext SLIT("are overlapped")))
+ 12 (vcat $ map (ppr_eqn kind sty) qs)
+
+dsIncompleteWarn :: DsMatchContext -> [ExhaustivePat] -> DsM ()
+dsIncompleteWarn ctx@(DsMatchContext kind _ _) pats = dsWarn warn
+ where
+ warn sty | length pats > maximum_output =
+ hang (pp_context sty ctx (ptext SLIT("are non-exhaustive")))
+ 12 (hang (ptext SLIT("Patterns not recognized:"))
+ 4 ((vcat $ map (ppr_incomplete_pats kind sty) (take maximum_output pats))
+ $$ ptext SLIT("...")))
+ warn sty =
+ hang (pp_context sty ctx (ptext SLIT("are non-exhaustive")))
+ 12 (hang (ptext SLIT("Patterns not recognized:"))
+ 4 (vcat $ map (ppr_incomplete_pats kind sty) pats))
+
+pp_context sty NoMatchContext msg = ptext SLIT("Warning: Some match(es)") <+> msg
+
+pp_context sty (DsMatchContext kind pats loc) msg
+ = hang (hcat [ppr (PprForUser opt_PprUserLength) loc, ptext SLIT(": ")])
+ 4 (hang message
+ 4 (pp_match kind pats))
+ where
+ message = ptext SLIT("Warning: Pattern match(es)") <+> msg
+
+ pp_match (FunMatch fun) pats
+ = hsep [ptext SLIT("in the definition of function"), ppr sty fun]
+
+ pp_match CaseMatch pats
+ = hang (ptext SLIT("in a group of case alternatives beginning:"))
+ 4 (ppr_pats sty pats)
+
+ pp_match PatBindMatch pats
+ = hang (ptext SLIT("in a pattern binding:"))
+ 4 (ppr_pats sty pats)
+
+ pp_match LambdaMatch pats
+ = hang (ptext SLIT("in a lambda abstraction:"))
+ 4 (ppr_pats sty pats)
+
+ pp_match DoBindMatch pats
+ = hang (ptext SLIT("in a `do' pattern binding:"))
+ 4 (ppr_pats sty pats)
+
+ pp_match ListCompMatch pats
+ = hang (ptext SLIT("in a `list comprension' pattern binding:"))
+ 4 (ppr_pats sty pats)
+
+ pp_match LetMatch pats
+ = hang (ptext SLIT("in a `let' pattern binding:"))
+ 4 (ppr_pats sty pats)
+
+ppr_pats sty pats = pprQuote sty $ \ sty -> sep (map (ppr sty) pats)
+
+separator (FunMatch _) = SLIT("=")
+separator (CaseMatch) = SLIT("->")
+separator (LambdaMatch) = SLIT("->")
+separator (PatBindMatch) = panic "When is this used?"
+separator (DoBindMatch) = SLIT("<-")
+separator (ListCompMatch) = SLIT("<-")
+separator (LetMatch) = SLIT("=")
+
+ppr_shadow_pats kind sty pats = pprQuote sty $ \ sty ->
+ sep [sep (map (ppr sty) pats), ptext (separator kind), ptext SLIT("...")]
+
+ppr_incomplete_pats kind sty (pats,[]) = pprQuote sty $ \ sty ->
+ sep [sep (map (ppr sty) pats)]
+ppr_incomplete_pats kind sty (pats,constraints) = pprQuote sty $ \ sty ->
+ sep [sep (map (ppr sty) pats), ptext SLIT("with"),
+ sep (map (ppr_constraint sty) constraints)]
+
+
+ppr_constraint sty (var,pats) = sep [ppr sty var, ptext SLIT("`not_elem`"),ppr sty pats]
+
+ppr_eqn kind sty (EqnInfo _ _ pats _) = ppr_shadow_pats kind sty pats
+
+\end{code}
+
+
The function @match@ is basically the same as in the Wadler chapter,
except it is monadised, to carry around the name supply, info about
annotations, etc.
@@ -112,7 +247,6 @@ So, the full type signature:
\begin{code}
match :: [Id] -- Variables rep'ing the exprs we're matching with
-> [EquationInfo] -- Info about patterns, etc. (type synonym below)
- -> [EquationInfo] -- Potentially shadowing equations above this one
-> DsM MatchResult -- Desugared result!
\end{code}
@@ -159,29 +293,19 @@ than the Wadler-chapter code for @match@ (p.~93, first @match@ clause).
And gluing the ``success expressions'' together isn't quite so pretty.
\begin{code}
-match [] eqns_info shadows
- = complete_matches eqns_info (any eqn_cant_fail shadows)
+match [] eqns_info
+ = complete_matches eqns_info
where
- complete_matches [eqn] is_shadowed
- = complete_match eqn is_shadowed
+ complete_matches [eqn]
+ = complete_match eqn
- complete_matches (eqn:eqns) is_shadowed
- = complete_match eqn is_shadowed `thenDs` \ match_result1 ->
- complete_matches eqns (is_shadowed || eqn_cant_fail eqn) `thenDs` \ match_result2 ->
+ complete_matches (eqn:eqns)
+ = complete_match eqn `thenDs` \ match_result1 ->
+ complete_matches eqns `thenDs` \ match_result2 ->
combineMatchResults match_result1 match_result2
- -- If at this stage we find that at least one of the shadowing
- -- equations is guaranteed not to fail, then warn of an overlapping pattern
- complete_match (EqnInfo [] match_result@(MatchResult _ _ _ cxt)) is_shadowed
- | opt_WarnOverlappedPatterns && is_shadowed =
- dsShadowWarn cxt `thenDs` \ _ ->
- returnDs match_result
-
- | otherwise = returnDs match_result
-
- eqn_cant_fail :: EquationInfo -> Bool
- eqn_cant_fail (EqnInfo [] (MatchResult CanFail _ _ _)) = False
- eqn_cant_fail (EqnInfo [] (MatchResult CantFail _ _ _)) = True
+ complete_match (EqnInfo _ _ [] match_result@(MatchResult _ _ _))
+ = returnDs match_result
\end{code}
%************************************************************************
@@ -203,17 +327,16 @@ Wadler-chapter @match@ (p.~93, last clause), and @match_unmixed_blk@
corresponds roughly to @matchVarCon@.
\begin{code}
-match vars@(v:vs) eqns_info shadows
+match vars@(v:vs) eqns_info
= mapDs (tidyEqnInfo v) eqns_info `thenDs` \ tidy_eqns_info ->
- mapDs (tidyEqnInfo v) shadows `thenDs` \ tidy_shadows ->
let
tidy_eqns_blks = unmix_eqns tidy_eqns_info
in
- match_unmixed_eqn_blks vars tidy_eqns_blks tidy_shadows
+ match_unmixed_eqn_blks vars tidy_eqns_blks
where
unmix_eqns [] = []
unmix_eqns [eqn] = [ [eqn] ]
- unmix_eqns (eq1@(EqnInfo (p1:p1s) _) : eq2@(EqnInfo (p2:p2s) _) : eqs)
+ unmix_eqns (eq1@(EqnInfo _ _ (p1:p1s) _) : eq2@(EqnInfo _ _ (p2:p2s) _) : eqs)
= if ( (irrefutablePat p1 && irrefutablePat p2)
|| (isConPat p1 && isConPat p2)
|| (isLitPat p1 && isLitPat p2) ) then
@@ -230,19 +353,16 @@ match vars@(v:vs) eqns_info shadows
-- subsequent blocks create a "fail expr" for the first one...
match_unmixed_eqn_blks :: [Id]
-> [ [EquationInfo] ] -- List of eqn BLOCKS
- -> [EquationInfo] -- Shadows
-> DsM MatchResult
- match_unmixed_eqn_blks vars [] shadows = panic "match_unmixed_eqn_blks"
+ match_unmixed_eqn_blks vars [] = panic "match_unmixed_eqn_blks"
- match_unmixed_eqn_blks vars [eqn_blk] shadows = matchUnmixedEqns vars eqn_blk shadows
+ match_unmixed_eqn_blks vars [eqn_blk] = matchUnmixedEqns vars eqn_blk
- match_unmixed_eqn_blks vars (eqn_blk:eqn_blks) shadows
- = matchUnmixedEqns vars eqn_blk shadows `thenDs` \ match_result1 -> -- try to match with first blk
- match_unmixed_eqn_blks vars eqn_blks shadows' `thenDs` \ match_result2 ->
+ match_unmixed_eqn_blks vars (eqn_blk:eqn_blks)
+ = matchUnmixedEqns vars eqn_blk `thenDs` \ match_result1 -> -- try to match with first blk
+ match_unmixed_eqn_blks vars eqn_blks `thenDs` \ match_result2 ->
combineMatchResults match_result1 match_result2
- where
- shadows' = eqn_blk ++ shadows
\end{code}
Tidy up the leftmost pattern in an @EquationInfo@, given the variable @v@
@@ -284,9 +404,9 @@ tidyEqnInfo :: Id -> EquationInfo -> DsM EquationInfo
-- DsM'd because of internal call to "match".
-- "tidy1" does the interesting stuff, looking at
-- one pattern and fiddling the list of bindings.
-tidyEqnInfo v (EqnInfo (pat : pats) match_result)
+tidyEqnInfo v (EqnInfo n ctx (pat : pats) match_result)
= tidy1 v pat match_result `thenDs` \ (pat', match_result') ->
- returnDs (EqnInfo (pat' : pats) match_result')
+ returnDs (EqnInfo n ctx (pat' : pats) match_result')
tidy1 :: Id -- The Id being scrutinised
-> TypecheckedPat -- The pattern against which it is to be matched
@@ -520,36 +640,31 @@ Its arguments and results are the same as for the ``top-level'' @match@.
\begin{code}
matchUnmixedEqns :: [Id]
-> [EquationInfo]
- -> [EquationInfo] -- Shadows
-> DsM MatchResult
-matchUnmixedEqns [] _ _ = panic "matchUnmixedEqns: no names"
+matchUnmixedEqns [] _ = panic "matchUnmixedEqns: no names"
-matchUnmixedEqns all_vars@(var:vars) eqns_info shadows
+matchUnmixedEqns all_vars@(var:vars) eqns_info
| irrefutablePat first_pat
= ASSERT( irrefutablePats column_1_pats ) -- Sanity check
-- Real true variables, just like in matchVar, SLPJ p 94
- match vars remaining_eqns_info remaining_shadows
+ match vars remaining_eqns_info
| isConPat first_pat
= ASSERT( patsAreAllCons column_1_pats )
- matchConFamily all_vars eqns_info shadows
+ matchConFamily all_vars eqns_info
| isLitPat first_pat
= ASSERT( patsAreAllLits column_1_pats )
-- see notes in MatchLiteral
-- not worried about the same literal more than once in a column
-- (ToDo: sort this out later)
- matchLiterals all_vars eqns_info shadows
+ matchLiterals all_vars eqns_info
where
first_pat = head column_1_pats
- column_1_pats = [pat | EqnInfo (pat:_) _ <- eqns_info]
- remaining_eqns_info = [EqnInfo pats match_result | EqnInfo (_:pats) match_result <- eqns_info]
- remaining_shadows = [EqnInfo pats match_result | EqnInfo (pat:pats) match_result <- shadows,
- irrefutablePat pat ]
- -- Discard shadows which can be refuted, since they don't shadow
- -- a variable
+ column_1_pats = [pat | EqnInfo _ _ (pat:_) _ <- eqns_info]
+ remaining_eqns_info = [EqnInfo n ctx pats match_result | EqnInfo n ctx (_:pats) match_result <- eqns_info]
\end{code}
%************************************************************************
@@ -601,13 +716,19 @@ matchWrapper :: DsMatchKind -- For shadowing warning messages
-> [TypecheckedMatch] -- Matches being desugared
-> String -- Error message if the match fails
-> DsM ([Id], CoreExpr) -- Results
+\end{code}
--- a special case for the common ...:
--- just one Match
--- lots of (all?) unfailable pats
--- e.g.,
--- f x y z = ....
+ a special case for the common ...:
+ just one Match
+ lots of (all?) unfailable pats
+ e.g.,
+ f x y z = ....
+
+ This special case have been ``undone'' due to problems with the new warnings
+ messages (Check.lhs.check). We need there the name of the variables to be able to
+ print later the equation. JJQC 30-11-97
+\begin{old_code}
matchWrapper kind [(PatMatch (VarPat var) match)] error_string
= matchWrapper kind [match] error_string `thenDs` \ (vars, core_expr) ->
returnDs (var:vars, core_expr)
@@ -622,28 +743,43 @@ matchWrapper kind [(GRHSMatch
= dsBinds False{-don't auto-scc-} binds `thenDs` \ core_binds ->
dsExpr expr `thenDs` \ core_expr ->
returnDs ([], mkCoLetsAny core_binds core_expr)
+\end{old_code}
-----------------------------------------------------------------------------
--- and all the rest... (general case)
+ And all the rest... (general case)
+
+
+ There is one small problem with the Lambda Patterns, when somebody
+ writes something similar to:
+ (\ (x:xs) -> ...)
+ he/she don't want a warning about incomplete patterns, that is done with
+ the flag opt_WarnSimplePatterns.
+ This problem also appears in the :
+ do patterns, but if the do can fail it creates another equation if the match can
+ fail (see DsExpr.doDo function)
+ let patterns, are treated by matchSimply
+ List Comprension Patterns, are treated by matchSimply also
+
+We can't call matchSimply with Lambda patterns, due to lambda patterns can have more than
+one pattern, and match simply only accepts one pattern.
+
+JJQC 30-Nov-1997
+
+\begin{code}
matchWrapper kind matches error_string
- = flattenMatches kind matches `thenDs` \ eqns_info@(EqnInfo arg_pats (MatchResult _ result_ty _ _) : _) ->
+ = flattenMatches kind 1 matches `thenDs` \ eqns_info@(EqnInfo _ _ arg_pats (MatchResult _ result_ty _) : _) ->
selectMatchVars arg_pats `thenDs` \ new_vars ->
- match new_vars eqns_info [] `thenDs` \ match_result ->
+ match_fun new_vars eqns_info `thenDs` \ match_result ->
mkErrorAppDs pAT_ERROR_ID result_ty error_string `thenDs` \ fail_expr ->
- -- Check for incomplete pattern match
- (case match_result of
- MatchResult CanFail result_ty match_fn cxt
- | opt_WarnIncompletePatterns
- -> dsIncompleteWarn cxt
- other -> returnDs ()
- ) `thenDs` \ _ ->
-
extractMatchResult match_result fail_expr `thenDs` \ result_expr ->
returnDs (new_vars, result_expr)
+ where match_fun = case kind of
+ LambdaMatch | opt_WarnSimplePatterns -> matchExport
+ | otherwise -> match
+ _ -> matchExport
\end{code}
%************************************************************************
@@ -658,32 +794,37 @@ pattern. It returns an expression.
\begin{code}
matchSimply :: CoreExpr -- Scrutinee
- -> TypecheckedPat -- Pattern it should match
- -> Type -- Type of result
+ -> DsMatchKind -- Match kind
+ -> TypecheckedPat -- Pattern it should match
+ -> Type -- Type of result
-> CoreExpr -- Return this if it matches
-> CoreExpr -- Return this if it does
-> DsM CoreExpr
-matchSimply (Var var) pat result_ty result_expr fail_expr
- = match [var] [eqn_info] [] `thenDs` \ match_result ->
- extractMatchResult match_result fail_expr
+matchSimply (Var var) kind pat result_ty result_expr fail_expr
+ = getSrcLocDs `thenDs` \ locn ->
+ let
+ ctx = DsMatchContext kind [pat] locn
+ eqn_info = EqnInfo 1 ctx [pat] initial_match_result
+ in
+ match_fun [var] [eqn_info] `thenDs` \ match_result ->
+ extractMatchResult match_result fail_expr
where
- eqn_info = EqnInfo [pat] initial_match_result
- initial_match_result = MatchResult CantFail
- result_ty
- (\ ignore -> result_expr)
- NoMatchContext
-
-matchSimply scrut_expr pat result_ty result_expr msg
- = newSysLocalDs (outPatType pat) `thenDs` \ scrut_var ->
- matchSimply (Var scrut_var) pat result_ty result_expr msg `thenDs` \ expr ->
+ initial_match_result = MatchResult CantFail result_ty (\ ignore -> result_expr)
+ match_fun = if opt_WarnSimplePatterns
+ then matchExport
+ else match
+
+matchSimply scrut_expr kind pat result_ty result_expr msg
+ = newSysLocalDs (outPatType pat) `thenDs` \ scrut_var ->
+ matchSimply (Var scrut_var) kind pat result_ty result_expr msg `thenDs` \ expr ->
returnDs (Let (NonRec scrut_var scrut_expr) expr)
-extractMatchResult (MatchResult CantFail _ match_fn _) fail_expr
+extractMatchResult (MatchResult CantFail _ match_fn) fail_expr
= returnDs (match_fn (error "It can't fail!"))
-extractMatchResult (MatchResult CanFail result_ty match_fn cxt) fail_expr
+extractMatchResult (MatchResult CanFail result_ty match_fn) fail_expr
= mkFailurePair result_ty `thenDs` \ (fail_bind_fn, if_it_fails) ->
returnDs (Let (fail_bind_fn fail_expr) (match_fn if_it_fails))
\end{code}
@@ -700,37 +841,40 @@ This is actually local to @matchWrapper@.
\begin{code}
flattenMatches
:: DsMatchKind
+ -> EqnNo
-> [TypecheckedMatch]
-> DsM [EquationInfo]
-flattenMatches kind [] = returnDs []
+flattenMatches kind n [] = returnDs []
-flattenMatches kind (match : matches)
- = flatten_match [] match `thenDs` \ eqn_info ->
- flattenMatches kind matches `thenDs` \ eqn_infos ->
+flattenMatches kind n (match : matches)
+ = flatten_match [] n match `thenDs` \ eqn_info ->
+ flattenMatches kind (n+1) matches `thenDs` \ eqn_infos ->
returnDs (eqn_info : eqn_infos)
where
flatten_match :: [TypecheckedPat] -- Reversed list of patterns encountered so far
+ -> EqnNo
-> TypecheckedMatch
-> DsM EquationInfo
- flatten_match pats_so_far (PatMatch pat match)
- = flatten_match (pat:pats_so_far) match
+ flatten_match pats_so_far n (PatMatch pat match)
+ = flatten_match (pat:pats_so_far) n match
- flatten_match pats_so_far (GRHSMatch (GRHSsAndBindsOut grhss binds ty))
+ flatten_match pats_so_far n (GRHSMatch (GRHSsAndBindsOut grhss binds ty))
= dsBinds False{-don't auto-scc-} binds `thenDs` \ core_binds ->
dsGRHSs ty kind pats grhss `thenDs` \ match_result ->
- returnDs (EqnInfo pats (mkCoLetsMatchResult core_binds match_result))
+ getSrcLocDs `thenDs` \ locn ->
+ returnDs (EqnInfo n (DsMatchContext kind pats locn) pats
+ (mkCoLetsMatchResult core_binds match_result))
where
pats = reverse pats_so_far -- They've accumulated in reverse order
- flatten_match pats_so_far (SimpleMatch expr)
+ flatten_match pats_so_far n (SimpleMatch expr)
= dsExpr expr `thenDs` \ core_expr ->
getSrcLocDs `thenDs` \ locn ->
- returnDs (EqnInfo pats
+ returnDs (EqnInfo n (DsMatchContext kind pats locn) pats
(MatchResult CantFail (coreExprType core_expr)
- (\ ignore -> core_expr)
- (DsMatchContext kind pats locn)))
+ (\ ignore -> core_expr)))
-- the matching can't fail, so we won't generate an error message.
where