Parser/Type error for + and - about write-you-a-haskell HOT 2 OPEN

In fact, the error is on this line. If you revert the way terms are parsed, all will be good. ie. Ex.buildExpressionParser table aexp. I don't quite understand the new code, and why it sort of works for some operators...

from write-you-a-haskell.

I think i found the problem: The "+" character is parsed as a positive sign inside Tok.integer lexer. I fixed the problem this way:

Parser.hs, line 20

integer :: Parser Integer
integer = Tok.natural lexer

Parser.hs line, 82

aexp :: Parser Expr
aexp = do
  r <- many1 $ choice [parens expr,bool,number,ifthen,fix,try letrecin, letin, lambda, variable]
  return $ foldr1 App r

expr :: Parser Expr
expr = Ex.buildExpressionParser table aexp

from write-you-a-haskell.