shithub: MicroHs

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A hack to allow 'a ~ b =>' in existential/GADT contexts.  Fixes issue #75

--- a/src/MicroHs/Parse.hs

+++ b/src/MicroHs/Parse.hs

@@ -405,7 +405,10 @@

 pContext :: P [EConstraint]

 pContext = (pCtx <* pDRArrow) <|< pure []

   where

-    pCtx = ((:[]) <$> pTypeApp)

+    pCtx =     ((:[]) <$> pTypeApp)

+           <|> (eq <$> pTypeArg <*> pTilde <*> pTypeArg)   -- A hack to allow   a~b => ...

+    eq t1 i t2 = [eApp2 (EVar i) t1 t2]

+    pTilde = do i <- pQSymOper; guard (i == mkIdent "~"); return i

 pDRArrow :: P ()

 pDRArrow = pSymbol "=>" <|< pSymbol "\x21d2"