On Jan 10, 2008 11:54 PM, Luke Palmer
Can someone explain what the heck is going on here?
Evaluating (const EXPR) creates a closure object with a pointer to 'const' and a pointer to the EXPR thunk. Call this closure object C. Evaluating (C undefined) calls 'const' with the EXPR and C thunks as its arguments, which returns the EXPR thunk. The EXPR thunk is then forced by your code. Evaluating (C undefined) again calls 'const' with the EXPR and C pointers as its arguments again, which again returns the *now forced* EXPR thunk. I.e., evaluating (const EXPR) creates a closure with a pointer to a single EXPR thunk, and then applying the same closure to some argument multiple times uses that same EXPR thunk every time. An unoptimized (\_ -> EXPR) creates a new thunk each time the function is applied to an argument. Hope that helps with understanding what is going on? - Benja