On Oct 17, 2006, at 1:37 PM, Víctor A. Rodríguez wrote:
What's wrong with doing it this way?
-- ** UNTESTED CODE **
verifyAdd :: Int -> Int -> Int -> Bool
verifyAdd a b sum | a + b == sum = True
otherwise = False
testAddMundane :: Int -> Int -> Bool
testAddMundane a b = verifyAdd a b (a + b)
-- all the IO-dependent stuff is below this line --
testAddRandom :: IO Bool
testAddRandom = do a <- randomIO
b <- randomIO
return verifyAdd a b (a + b)
I discovered something worst yet :-P
Using the next code and calling verifyAdd or testAddMundane it says :
Program error: verifyAdd: ERROR
Instead calling testAddRandom only says :
:: IO Bool
(55 reductions, 92 cells)
This is due to the magic of lazy evaluation. You never use the
result of 'testAddRandom', so it's never evaluated, which means your
call to 'error' is also never evaluated.
Type:
testAddRandom >>= print
on the command line and you should get the same error, because the
call to 'print' demands the result of running testAddRandom.
---- CODE STARTS HERE, AND IS TESTED -----
import Random
verifyAdd :: Int -> Int -> Int -> Bool
verifyAdd a b sum = error "verifyAdd: ERROR"
testAddMundane :: Int -> Int -> Bool
testAddMundane a b = verifyAdd a b (a + b)
-- all the IO-dependent stuff is below this line --
testAddRandom :: IO Bool
testAddRandom = do a <- randomIO
b <- randomIO
return ( verifyAdd a b (a+b) )
--
Víctor A. Rodríguez (http://www.bit-man.com.ar)
El bit Fantasma (Bit-Man)
Perl Mongers Capital Federal (http://cafe.pm.org/)
GNU/Linux User Group - FCEyN - UBA (http://glugcen.dc.uba.ar/)
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Rob Dockins
Speak softly and drive a Sherman tank.
Laugh hard; it's a long way to the bank.
-- TMBG
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
