
Yes that if block did get indented incorrectly in the posting. However, I like how the guards work for this, and as soon as I used your recommendation, it started working. Great, my first Haskell program, albeit with a little help, I appreciate it. David Menendez-2 wrote:
On Mon, Dec 21, 2009 at 11:14 PM, joeltt
wrote: I'm trying to write my first Haskell program. The below is the first real logic block I've tried to write, unfortunately I get a "The last statement in a 'do' construct must be an expression" error when loading the method. However, the location of this problem isn't very clear. Is there a way to get more detailed parse message from Haskell, or can someone tell me where the problem is (and better "why"?). I don't think I actually need to use a "do" IO/Monad theme here, but its not clear to me either way. This isn't homework, its just for fun...
do_solve_iter guess tried = do let actual = count_occurences guess if guess == actual then putStrLn "ANSWER!!" else if (find (==actual) tried) == Just actual then do putStrLn "NO ANSWER!" putStrLn tried else do putStrLn "ITER" do_solve_iter actual (actual : tried)
Assuming your indentation didn't get lost in transmission, your problem is the line "if guess == actual", which needs to be at the same level of indentation as "let actual...". As written, the do-block is terminating after the let-statement, which isn't permitted.
Also, unless there is more to the function, you don't really need the outermost do-block at all. You can rewrite it easily as a let...in expression, or move the definition of actual to a where clause and use guards to avoid the nested if-expressions.
do_solve_iter guess tried | guess == actual = putStrLn "ANSWER!!" | find (==actual) tried == Just actual = do putStrLn "NO ANSWER" putStrLn tried | otherwise = do putStrLn "ITER" do_solve_iter actual (actual : tried) where actual = count_occurences guess
-- Dave Menendez
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