POSTPONE

Interpretation:

Interpretation semantics for this word are undefined.

Compilation:

( "<spaces>name" -- )

Skip leading space delimiters. Parse name delimited by a space. Find name. Append the compilation semantics of name to the current definition. An ambiguous condition exists if name is not found.

See:

Rationale:

Typical use:

   : ENDIF POSTPONE THEN ; IMMEDIATE

   : X ... IF ... ENDIF ... ;

POSTPONE replaces most of the functionality of COMPILE and [COMPILE]. COMPILE and [COMPILE] are used for the same purpose: postpone the compilation behavior of the next word in the parse area. COMPILE was designed to be applied to non-immediate words and [COMPILE] to immediate words. This burdens the programmer with needing to know which words in a system are immediate. Consequently, Forth standards have had to specify the immediacy or non-immediacy of all words covered by the standard. This unnecessarily constrains implementors.

A second problem with COMPILE is that some programmers have come to expect and exploit a particular implementation, namely:

   : COMPILE R> DUP @ , CELL+ >R ;

This implementation will not work on native code Forth systems. In a native code Forth using inline code expansion and peephole optimization, the size of the object code produced varies; this information is difficult to communicate to a "dumb" COMPILE. A "smart" (i.e., immediate) COMPILE would not have this problem, but this was forbidden in previous standards.

For these reasons, COMPILE has not been included in the standard and [COMPILE] has been moved in favor of POSTPONE. Additional discussion can be found in Hayes, J.R., "Postpone", Proceedings of the 1989 Rochester Forth Conference.

Testing:

T{ : GT4 POSTPONE GT1 ; IMMEDIATE -> }T
T{ : GT5 GT4 ; -> }T
T{ GT5 -> 123 }T

T{ : GT6 345 ; IMMEDIATE -> }T
T{ : GT7 POSTPONE GT6 ; -> }T
T{ GT7 -> 345 }T

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