World: r4wp

hmm, okay

i don't follow your point re: recursing from anywhere (i.e., from 
non-tail position)

via the use of throw/catch

if you're not in tail position you'd still have to push stack frames

Marc's code is an implementation of tail-recursive function. Such 
implementations have been posted by some people in the past, but 
there are some minor differences between them. For example, the way 
how the arguments were passed differed from Marc's idea.

I thought you wanted to simulate tail/recursion only (it's what youre 
current code do anyway)
in that case you don't need to store the stack frame

To answer to the question: why tail recursion from anywhere ?
What if you want conditionned recursion ? 
Recurse could appear inside a IF block not at at the tail.

aha, misunderstood your point

yes, there's a shortcoming if you're recursing from within a conditional 
-- thanks for spotting that; will rework

fix: http://0branch.com/highlight/snippets/rfunc3.r

though there's still the while loop wrapping the body

The WHILE loop is necessary for what you are doing, do not worry 
about it.

damned silly mistakes -- was focused on getting the bindings etc. 
right, overlooked this prob

thanks for the help guys

The usage comment in the third version is very nice. 


On doc strings, try to keep them short, leaving detailed notes to 
the usage or other comments. e.g.

rfunc: func [

    {Defines a tail-call optimized user function, using RECUR for self-calls.}
    spec [block!] "Function spec (see: func)"
    body [block!] "Function body (modified) (see: func)"
    /local wrapped
] [
    ...
] 

Short doc strings are nicer with HELP.

thanks for the tip

Also, I try to use special names for augmentations and such. In this 
case, 'with would conflict with my WITH func.

hmm, yeah -- was wondering about that

that was originally _args_ but i switched it out so that you could 
get a more readable recur call (i.e., cheekily make use of 'with' 
so that it read better)

(for the BIND)

Easy enough to add sigils to make it special. I don't general go 
as far as a gensym approach for things like this.

Yes. Too early for my brain here, but 'is known-word honored in the 
bind? e.g. "set with reduce (args)"

That is, 'with is special no matter what known-word you use, correct?

Marc, your "private variables" like 'with, _recur_ can be made more 
private not needing to use the PROtECT function, in fact.

Ah, no, I think I get it now.

I don't think you need 'with  at all, you can throw back the new 
parameters as an argument of the throw function, like:
>> throw/name reduce args 'recurse

also, there is a problem with the result I think

(I mean the function result)

steeve: ooh, good point

ladislav: ah yes, there is

Here is a version with no locals, no temporary context, no shit and 
not tested ;-)

rfunc: func [spec body][
	func spec compose/deep [
		forever [
		   set [(spec)] catch/name [
			  return (func spec body) (spec)
		   ] 'recur
		]
	]
]
recur: func [args][throw/name reduce args 'recur]

wow

works well - full thing here: http://0branch.com/highlight/snippets/rfunc4.r

to return a value and stop the function you need to use 'return instead 
of 'break

I think

recur (Must be in tail position)
 -> not needed anymore

well, it has to be a tail call

it's a tail call but it can be anywhere in the function body

so you couldn't do   x + recur [ y ]

sounds like we mean different things by 'tail position'

it seems

Yep, it seems

Yep, it seems

i mean this: http://en.wikipedia.org/wiki/Tail_call

(lag)

It's tail call recursion yes, but tail position usualy means "physically 
placed" at the tail (in our context, at the end of the body of the 
function)
Anyway...

not be pedantic, but i linked to that for the opening two sentences:


In computer science, a tail call is a subroutine call that happens 
inside another procedure as its final action; it may produce a return 
value which is then immediately returned by the calling procedure. 
The call site is then said to be in tail position, i.e. at the end 
of the calling procedure.

Okay T_T

i've never heard tail position refer to last 'physical place'

anyway, not important