diff options
Diffstat (limited to 'compiler/typecheck/TcEvidence.hs')
| -rw-r--r-- | compiler/typecheck/TcEvidence.hs | 18 |
1 files changed, 17 insertions, 1 deletions
diff --git a/compiler/typecheck/TcEvidence.hs b/compiler/typecheck/TcEvidence.hs index 72aed23505..eb65d1e093 100644 --- a/compiler/typecheck/TcEvidence.hs +++ b/compiler/typecheck/TcEvidence.hs @@ -8,7 +8,8 @@ module TcEvidence ( HsWrapper(..), (<.>), mkWpTyApps, mkWpEvApps, mkWpEvVarApps, mkWpTyLams, mkWpLams, mkWpLet, mkWpCastN, mkWpCastR, collectHsWrapBinders, - mkWpFun, mkWpFuns, idHsWrapper, isIdHsWrapper, pprHsWrapper, + mkWpFun, mkWpFuns, idHsWrapper, isIdHsWrapper, isErasableHsWrapper, + pprHsWrapper, -- Evidence bindings TcEvBinds(..), EvBindsVar(..), @@ -355,6 +356,21 @@ isIdHsWrapper :: HsWrapper -> Bool isIdHsWrapper WpHole = True isIdHsWrapper _ = False +-- | Is the wrapper erasable, i.e., will not affect runtime semantics? +isErasableHsWrapper :: HsWrapper -> Bool +isErasableHsWrapper = go + where + go WpHole = True + go (WpCompose wrap1 wrap2) = go wrap1 && go wrap2 + -- not so sure about WpFun. But it eta-expands, so... + go WpFun{} = False + go WpCast{} = True + go WpEvLam{} = False -- case in point + go WpEvApp{} = False + go WpTyLam{} = True + go WpTyApp{} = True + go WpLet{} = False + collectHsWrapBinders :: HsWrapper -> ([Var], HsWrapper) -- Collect the outer lambda binders of a HsWrapper, -- stopping as soon as you get to a non-lambda binder |