Hi there,
I have a problem where I like to update a record with an IO a. Not
quite sure how to describe it.
Here is a minimal example: I get a list of numbers from the command
line and I like to add those numbers n and randome numbers from a
range from [0..n] in two fields of a record.
<---------------------------snip---------------------------->
module Main where
import System.Environment.UTF8
import System.Random
data NumRec = NumRec {
mxV :: Int,
mxR :: Int
} deriving (Show,Read)
initNumRec = NumRec { mxV = 0, mxR = 0 }
toInt s = read s :: Int
addRandom m n = do
let mxv = mxV m
let mxr = mxR m
let r = rand n
m { mxV = mxv + n,
mxR = mxr + r }
rand :: Int -> IO Int
rand max = getStdRandom (randomR (0, max))
main = do
args <- getArgs
print args
let ilist = map toInt args
let mixed = foldl addRandom initNumRec ilist
print mixed
<---------------------------snap---------------------------->
I get the following error when compiling:
[1 of 1] Compiling Main ( minimal.hs, minimal.o )
minimal.hs:22:23:
Couldn't match expected type `Int' with actual type `IO Int'
In the second argument of `(+)', namely `r'
In the `mxR' field of a record
In the expression: m {mxV = mxv + n, mxR = mxr + r}
How can I correct the compile error?
--
Manfred
