Thanks guys, I understand what you're telling me, but have some nested IFs and just want to fall through on one of the ELSES but then I end up with two ELSES in a row and nothing between them. Oh, well, on to restructuring.
Michael --- On Wed, 10/21/09, Tim Wawrzynczak <[email protected]> wrote: From: Tim Wawrzynczak <[email protected]> Subject: Re: [Haskell-cafe] Is there a null statement that does nothing? To: "michael rice" <[email protected]> Cc: [email protected] Date: Wednesday, October 21, 2009, 8:49 PM Yes, an if statement must have both 'then' and 'else' branches. As an example, what if you had let a = if b == 2 then True else False and you were missing an else branch? What would 'a' get assigned to? The if statement "returns" a value so must have both branches. However, in a monadic constraint, there are the functions 'when' and 'unless.' They allow conditional evaluation of expressions in a monadic context. For example, main = do line <- getLine when (line == "hello") putStrLn "Hello back!" Cheers, - Tim On Wed, Oct 21, 2009 at 7:43 PM, michael rice <[email protected]> wrote: It looks like both the THEN and the ELSE in an IF expression must each have an expression. What's a graceful way to do nothing in either or both slots, kind of like the Fortran CONTINUE statement. --mr ================ [mich...@localhost ~]$ ghci GHCi, version 6.10.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. Prelude> if (1==1) then else <interactive>:1:15: parse error on input `else' Prelude> if (1==1) then True else <interactive>:1:24: parse error (possibly incorrect indentation) Prelude> if (1==1) then True else False True Prelude> _______________________________________________ Haskell-Cafe mailing list [email protected] http://www.haskell.org/mailman/listinfo/haskell-cafe
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