In case of +, the reason might be that it's cheap, but the function add could do something else than + (It was just a small example). Ok, thank you for your useful comments. I will read about cse. Heinrich On 18.02.2012 13:42, Victor Gorokgov wrote:
+ on Int is extremely cheap. It is always faster to add again rather than store the value. But Integer is a different story. Addition time on this type can grow to several minutes.
18.02.2012 13:28, Heinrich Hördegen пишет:
Dear all,
I have a question about evaluation with respect to types and currying. Consider this programm:
import Debug.Trace
-- add :: Integer -> Integer -> Integer add :: Int -> Int -> Int add x y = x + y
f a b c = trace "b" (add x c) where x = trace "a" (add a b)
main :: IO () main = do print (f 1 2 3) print (f 1 2 4)
Compiled with ghc-7.0.3:
$ ghc --make Main.hs -o main -O2
The function add has to types. When we use type Int -> Int -> Int, the programm produces "b a 6 b a 7" as output which shows that the x from the where clause in f is evaluated twice. However, when we use type Integer -> Integer -> Integer, this will give "b a 6 b 7" which shows that x is evaluated only once. This was rather unexpected to me.
Why does the number of evaluation steps depend on a type? Can anybody explain this or give a hint?
Thank you very much, Heinrich
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