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Date: | 2007-04-26 (09:17) |
From: | skaller <skaller@u...> |
Subject: | Re: [Caml-list] Function application implementation |
On Thu, 2007-04-26 at 10:52 +0200, Tom wrote: > > > On 26/04/07, skaller <skaller@users.sourceforge.net> wrote: > It knows the type of the function expression, and that is all > that is required. Incidentally Ocaml evaluates right to left. > So > > f x y z > > will be roughly: > > push (eval z) > push (eval y) > push (eval x) > push (eval f) > apply > apply > apply > > But that doesn't explain how does each apply know what to do, either > to build a new closure (in the case above, the first two applies) or > to actually call the code (the third apply). push (eval f) calculates the expression f, which results in a closure. Apply, with the stack: closure f <-- top value 1 ... calculates apply(closure f, value 1) That is how functions are called. In practice, a compiler may do optimisations. In the Felix compiler for example, in the expression: apply(f,e) if the subexpresion f is a simple function constant, then the compiler can inline the function. Otherwise, a closure has to be formed. In Felix this means instantiating a C++ class (the function f) to make a closure (an object of the class). In Felix the actual C++ used is: (new f(environment)) -> apply (e) In other words, all compilers will look for optimisations such as are made possible when a direct call is detected, inlining in such cases being one possible optimisation which could be applied. the actual sequence I have above may not be how the Ocaml compiler organises it: the point is that the model is built to not need to make the distinction you're asking about: that's just an optimisation. -- John Skaller <skaller at users dot sf dot net> Felix, successor to C++: http://felix.sf.net