candFromSymbol :: ((Id, TypeScheme) -> Maybe Term) -- ^ Definiens extractor
             -> Symbol -> Maybe MatchOp
candFromSymbol df (Symbol {symName = opid, symType = OpAsItemType typ}) =
    fmap ((,,) opid typ) $ df (opid, typ)
candFromSymbol :: ((Id, TypeScheme) -> Maybe Term) -- ^ Definiens extractor
             -> Symbol -> Maybe MatchOp
candFromSymbol df (Symbol {symName = opid, symType = OpAsItemType typ}) =
    fmap ((,,) opid typ) $ df (opid, typ)
candFromSymbol df (Symbol {symName = opid, symType = OpAsItemType typ}) =
    fmap ((,,) opid typ) $ df (opid, typ)