Using the Python Interpreter as a Reference

[Steven D'Aprano]

On Tue, 29 Nov 2011 13:57:32 +1100, Chris Angelico wrote:

> I'm inclined toward an alternative: explicit recursion. Either a
> different syntax, or a special-case on the use of the function's own
> name, but whichever syntax you use, it compiles in a "recurse" opcode.
> That way, if name bindings change, it's still going to recurse -
> something few languages guarantee, and therefore few languages can
> optimize.

As I recall, Forth uses (or used) a special RECURSE word which turned on 
the recursion bit while compiling, so that the compiled word could see 
itself.

By memory, the (incomplete) definition:

: fact dup 1- fact * ;

would fail, unless you happened to already have another word called fact 
existing at compilation time. To make it recurse correctly, the compiler 
needs to make sure that the namespace fact sees includes itself:

RECURSE : fact dup 1- fact * ;

which should work, apart from the embarrassing fact that I don't recall 
the syntax for conditional jumps and so the recursion never terminates.

:)


-- 
Steven