Commit c7c96efc authored by simonpj's avatar simonpj
Browse files

[project @ 2003-11-06 09:42:45 by simonpj]

Import all instances in cases like C (a b)
parent bfc3c306
......@@ -446,6 +446,13 @@ Then, if we are trying to resolve (C Int x), we need (a)
if we are trying to resolve (C x [y]), we need *both* (b) and (c),
even though T is not involved yet, so that we spot the overlap.
NOTE: if you use an instance decl with NO type constructors
instance C a where ...
and look up an Inst that only has type variables such as (C (n o))
then GHC won't necessarily suck in the instances that overlap with this.
\begin{code}
loadImportedInsts :: Class -> [Type] -> TcM PackageInstEnv
loadImportedInsts cls tys
......@@ -467,7 +474,9 @@ loadImportedInsts cls tys
-- Suck in the instances
; let { (inst_pool', iface_insts)
= selectInsts (eps_insts eps) cls_gate tc_gates }
= WARN( null tc_gates, ptext SLIT("Interesting! No tycons in Inst:")
<+> pprClassPred cls tys )
selectInsts (eps_insts eps) cls_gate tc_gates }
-- Empty => finish up rapidly, without writing to eps
; if null iface_insts then
......@@ -504,16 +513,22 @@ selectInsts pool@(Pool insts n_in n_out) cls tycons
(insts', iface_insts)
= case lookupNameEnv insts cls of {
Nothing -> (insts, []) ;
Just gated_insts ->
Just gated_insts ->
case foldl choose ([],[]) gated_insts of {
case choose1 gated_insts of {
(_, []) -> (insts, []) ; -- None picked
(gated_insts', iface_insts') ->
(extendNameEnv insts cls gated_insts', iface_insts') }}
choose1 gated_insts
| null tycons -- Bizarre special case of C (a b); then there are no tycons
= ([], map snd gated_insts) -- Just grab all the instances, no real alternative
| otherwise -- Normal case
= foldl choose2 ([],[]) gated_insts
-- Reverses the gated decls, but that doesn't matter
choose (gis, decls) (gates, decl)
choose2 (gis, decls) (gates, decl)
| any (`elem` tycons) gates = (gis, decl:decls)
| otherwise = ((gates,decl) : gis, decls)
\end{code}
......
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