wiki:Commentary/Compiler/StrictnessAnalysis/Examples

Version 1 (modified by kirsten, 7 years ago) (diff)

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Strictness analysis: examples

Consider:

f g True = 3
f g False = g 1 2

...f (\ x -> let foo = somethingExpensive in \ y -> ...)...

We want to make sure to figure out that f's argument is demanded with type L1X(L1X(LMX)) -- that is, it may or may not be demanded, but if it is, it's always applied to two arguments. This shows why deferType shouldn't just throw away the argument info: in this case, the (\ x -> ...) expression has a nonstrict demand placed on it, yet we still care about the arguments.

On the other hand, in:

foo x y = 
  case x of
     A -> \ z -> x*z
     B -> \ z -> x+z

we want to say that if the result of foo has demand S placed on it (i.e., not a call demand), the body of foo has demand S placed on it, not S(LMX). So this case needs to be treated differently from the one above.