toFunType (FApp c [_,ity])
    | c == sUN "C_FnBase" = FFunction
    | c == sUN "C_FnIO" = FFunctionIO
toFunType (FApp c [_,ity])
    | c == sUN "C_FnBase" = FFunction
    | c == sUN "C_FnIO" = FFunctionIO
toFunType (FApp c [_,ity])
    | c == sUN "C_FnBase" = FFunction
    | c == sUN "C_FnIO" = FFunctionIO