• simonpj's avatar
    [project @ 2003-04-16 13:34:13 by simonpj] · 221b6b69
    simonpj authored
     Use the Infer/Check idea for typechecking higher-rank types
    The main idea is that
    	data Expected ty = Infer (TcRef ty) | Check ty
    	tcMonoExpr :: Expr -> Expected TcRhoType -> TcM Expra
    This "Expected" type tells tcMonoExpr whether it's doing inference or
    checking.  It replaces the "HoleTv" flavour of type variable.
    This actually leads to slightly more lines of code, but it's much
    clearer, and the new type distinctions showed up several subtle bugs
    in the previous implementation.  It all arose out of writing the
    prototype implementation for the paper.
    Error messages wibble around a little bit.  I'm not quite certain why!  But the
    changes look like improvements to me.