A transformation, described by Wadsworth in 1971, which ensures that subexpressions in a function body which do not depend on the function's arguments are only evaluated once. E.g. each time the function
f x = x + sqrt 4
is applied, (sqrt 4) will be evaluated. Since (sqrt 4) does not depend on x, we could transform this to:
f x = x + sqrt4
sqrt4 = sqrt 4
We have replaced the dynamically created (sqrt 4) with a single shared constant which, in a graph reduction system, will be evaluated the first time it is needed and then updated with its value.
See also fully lazy lambda lifting, let floating.