[Haskell-cafe] Laziness question

[michael rice]

From: http://en.wikibooks.org/wiki/Haskell/Laziness


Given two functions of one parameter, f and g, we say f is stricter than g if f x evaluates x to a deeper level than g x

Exercises

   1. Which is the stricter function?

f x = length [head x]
g x = length (tail x)



Prelude> let f x = length [head x]
Prelude> let g x = length (tail x)
Prelude> f undefined
1
Prelude> g undefined
*** Exception: Prelude.undefined
Prelude> 



So, g is stricter than f?

Wouldn't both functions need to evaluate x to the same level, *thunk* : *thunk* to insure listhood?

f x = length [head *thunk* : *thunk*]
g x = length (tail *thunk* : *thunk*)

Michael



      
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