Re: [Haskell-cafe] Arithmetic expressions with GADTs: parsing

On Wed, May 02, 2012 at 03:02:46PM +0300, Roman Cheplyaka wrote:

* j.romildo@gmail.com [2012-05-02 08:03:45-0300] [...] The alternatives given to <|> must be of the same type. In your case, one is Expr Double and one is Expr Bool.

Inclusion of pBool in pFactor is probably a mistake — unless you're going to multiply booleans.

You are right in the sense that I cannot mix Expr Bool and Expr Double in a (O op l r) expression. But the parser should be able to parse any form of expressions. So I rewrite my program to take this into account. The new versions still does not compile: Expr.hs:27:23: Couldn't match expected type `Double' with actual type `Bool' Expected type: ParsecT String () Data.Functor.Identity.Identity (Expr Double) Actual type: ParsecT String () Data.Functor.Identity.Identity (Expr Bool) In the first argument of `(<|>)', namely `pBool' In the second argument of `(<|>)', namely `pBool <|> pEqual' Romildo