Repository : ssh://darcs.haskell.org//srv/darcs/ghc On branch : master
http://hackage.haskell.org/trac/ghc/changeset/f27c631a16a17b8ad740d7d28c6ff267fb189c2c >--------------------------------------------------------------- commit f27c631a16a17b8ad740d7d28c6ff267fb189c2c Author: Simon Peyton Jones <[email protected]> Date: Wed Aug 29 10:57:48 2012 +0100 Fix Trac #7196 by adding a case to the desugarer Pls merge to 7.6 >--------------------------------------------------------------- compiler/deSugar/DsBinds.lhs | 11 ++++++----- compiler/typecheck/TcEvidence.lhs | 21 +++++++++++---------- 2 files changed, 17 insertions(+), 15 deletions(-) diff --git a/compiler/deSugar/DsBinds.lhs b/compiler/deSugar/DsBinds.lhs index 75680bc..4fa1ec0 100644 --- a/compiler/deSugar/DsBinds.lhs +++ b/compiler/deSugar/DsBinds.lhs @@ -844,13 +844,14 @@ ds_tc_coercion subst tc_co ds_scc :: CvSubst -> SCC EvBind -> CvSubst ds_scc subst (AcyclicSCC (EvBind v ev_term)) - = extendCvSubstAndInScope subst v (ds_ev_term subst ev_term) + = extendCvSubstAndInScope subst v (ds_co_term subst ev_term) ds_scc _ (CyclicSCC other) = pprPanic "ds_scc:cyclic" (ppr other $$ ppr tc_co) - ds_ev_term :: CvSubst -> EvTerm -> Coercion - ds_ev_term subst (EvCoercion tc_co) = ds_tc_coercion subst tc_co - ds_ev_term subst (EvId v) = ds_ev_id subst v - ds_ev_term _ other = pprPanic "ds_ev_term" (ppr other $$ ppr tc_co) + ds_co_term :: CvSubst -> EvTerm -> Coercion + ds_co_term subst (EvCoercion tc_co) = ds_tc_coercion subst tc_co + ds_co_term subst (EvId v) = ds_ev_id subst v + ds_co_term subst (EvCast tm co) = mkCoCast (ds_co_term subst tm) (ds_tc_coercion subst co) + ds_co_term _ other = pprPanic "ds_co_term" (ppr other $$ ppr tc_co) ds_ev_id :: CvSubst -> EqVar -> Coercion ds_ev_id subst v diff --git a/compiler/typecheck/TcEvidence.lhs b/compiler/typecheck/TcEvidence.lhs index 6ac351e..1214905 100644 --- a/compiler/typecheck/TcEvidence.lhs +++ b/compiler/typecheck/TcEvidence.lhs @@ -490,12 +490,13 @@ data EvLit \end{code} -Note [Coecion evidence terms] -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -Notice that a coercion variable (v :: t1 ~ t2) can be represented as an EvTerm -in two different ways: - EvId v - EvCoercion (TcCoVarCo v) +Note [Coercion evidence terms] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +An evidence term for a coercion, of type (t1 ~ t2), always takes one of +these forms: + co_tm ::= EvId v + | EvCoercion co + | EvCast co_tm co An alternative would be @@ -506,12 +507,12 @@ An alternative would be mkEvCast (EvCoercion c1) c2 = EvCoercion (TcCastCo c1 c2) mkEvCast t c = EvCast t c +I don't think it matters much... but maybe we'll find a good reason to +do one or the other. But currently we allow any of the three forms. + We do quite often need to get a TcCoercion from an EvTerm; see -'evTermCoercion'. Notice that as well as EvId and EvCoercion it may see -an EvCast. +'evTermCoercion'. -I don't think it matters much... but maybe we'll find a good reason to -do one or the other. Note [EvKindCast] ~~~~~~~~~~~~~~~~~ _______________________________________________ Cvs-ghc mailing list [email protected] http://www.haskell.org/mailman/listinfo/cvs-ghc
