Re: [Haskell-cafe] Last statement in 'do' must be an expression error.

On Thu, Aug 17, 2006 at 10:18:25AM +0200, Szymon Z??bkiewicz wrote:

To: haskell-cafe@haskell.org From: Szymon Z??bkiewicz Date: Thu, 17 Aug 2006 10:18:25 +0200 Subject: [Haskell-cafe] Last statement in 'do' must be an expression error.

Hi.

When trying to compilke this code:

{...} 8.if (a == 0) && (b == 0) 9. then do 10. nr1 <- read (prompt "enter 1. number: ") 11. nr2 <- read (prompt "enter 2. number: ")

each do block needs to evaluate to some value when performed. if you have nothing to return, do something like "return ()". (note this only works if the type checker is happy with it. possibly you need to restructure parts of the code you didn't post, too.)

12. else do 13. let nr1 = a 14. nr2 = b {...}

The compiler tells me thats there's an error on line 10: "The last statement in a 'do' construct mesy be an expression"

Could you tell me how to change it so that the "declaration" of the first nr1 and nr2 is still in the "then" block.

what about this code (untested)? do nr1 <- if a == 0 then read (prompt ":") else return a nr2 <- if b == 0 then read (prompt ":") else return b ... hth, m.