[Haskell-cafe] Why do I need a 'do'?

[michael rice]

Hi,

Why do I need a 'do' in the code below?

Michael

==================

import System.Random

rollDice :: IO Int
rollDice = getStdRandom (randomR (1,6))

rollNDice :: Int -> [IO Int]
rollNDice 0 = []
rollNDice n = rollDice : rollNDice (n-1)

=================

[michael at localhost ~]$ ghci rnd0
GHCi, version 6.10.1: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer ... linking ... done.
Loading package base ... linking ... done.
[1 of 1] Compiling Main             ( rnd0.hs, interpreted )
Ok, modules loaded: Main.
*Main> rollDice
Loading package old-locale-1.0.0.1 ... linking ... done.
Loading package old-time-1.0.0.1 ... linking ... done.
Loading package random-1.0.0.1 ... linking ... done.
6
*Main> rollDice
3
*Main> rollNDice 3

<interactive>:1:0:
    No instance for (Show (IO Int))
      arising from a use of `print' at <interactive>:1:0-10
    Possible fix: add an instance declaration for (Show (IO Int))
    In a stmt of a 'do' expression: print it
*Main> 




      
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