POSTPONE a deferred word.

[SirWumpus]

What does it mean to POSTPONE a deferred word? Is it ambiguous or is there some historical undocumented behaviour, like use the value of the deferred word at the time POSTPONE are applied?

(hypothetical example)

DEFER return IMMEDIATE

: alt_exit ( -- )
    ['] xyzzy ['] return DEFER!
    ...
    POSTPONE return
    ['] EXIT ['] return DEFER!
; IMMEDIATE

: woot ( x -- )
    ?DUP IF alt_exit THEN
    ...
;

So what happens when 0 woot executes? Does it follow EXIT or xyzzy?

Does something similar happen for COMPILE,?

[ruv]

What does it mean to POSTPONE a deferred word?

Nothing special. Same as for other user-defined words:

• if a deferred word foo is an ordinary word, then postpone foo is equivalent to ['] foo compile,;
• if a deferred word foo is an immediate word, then postpone foo is equivalent to ['] foo execute-compiling.

---

use the value of the deferred word at the time POSTPONE are applied?

Do you mean the compilation semantics of postpone or the run-time semantics that they appends?

(hypothetical example)

A standard program cannot tick exit (or, at least, execute the returned xt). Because it is not allowed to obtain the execution token of a word for which interpretation semantics are not defined by the standard. You can use [: POSTPONE EXIT ;] instead of ['] EXIT .

Because return is an immediate word, your definition for alt_exit is equivalent to the following:

: alt_exit ( -- )
    ['] xyzzy ['] return DEFER!
    ...
    ['] return execute-compiling
    [: POSTPONE EXIT ;] ['] return DEFER!
; IMMEDIATE

: woot ( x -- )
    ?DUP IF alt_exit THEN
    ...
;

So, the execution semantics of return are preformed before they are changed in the second time.
Hence, this definition for alt_exit is equivalent to the following:

: alt_exit ( -- )
    ['] xyzzy ['] return DEFER!
    ...
    ['] xyzzy execute-compiling
    [: POSTPONE EXIT ;] ['] return DEFER!
; IMMEDIATE

So what happens when 0 woot executes? Does it follow EXIT or xyzzy?

It follows xyzzy.

[ruv]

So what happens when 0 woot executes? Does it follow EXIT or xyzzy?

It follows xyzzy.

: woot ( x -- )
    ( x.some\0 | 0 ) ?DUP ( 0 | x.some x.some ) IF ( x.some ) alt_exit THEN
    ...
;

In fact, on 0 woot the run-time semantics at the point where alt_exit is used will not get control. They will get control on 1 woot.

[SirWumpus]

(Ugh. 1 woot yep. I blame the puppy for making me rush proof reading the question. Bad puppy🐶)