Compiling Programmatically

Semantics

Words can have different behaviour depending on whether we are in compilation mode or interpretation mode. The technical term for "behaviour" is semantics.

The default interpretation semantics of a word is to run its code section.
The default compilation semantics of a word is to append its code section to the enclosing new word being defined.
An immediate word breaks the default compilation semantics. The word's code section is run instead of being compiled into the enclosing word.
Some words may break both default semantics. Some words have no interpretation semantics.

Compiling

In some situations, you will have to compile code into a new word without expecting it to have the default compilation semantics. There are two words to help you with this.

Word	Action
[COMPILE]	Takes the following word and compiles the word's code section into the enclosing word, regardless of that word's compilation semantics.
COMPILE,	Takes a given XT and compiles its code section into the enclosing word.

Examples

Example 1

	
	: hi "Hi!" . ;
	: bb [compile] hi "bye!" . ;

	bb
	Hi! bye! ok
	
	see bb
	[0] HI
	[1] Literal(bye!)
	[2] .
	ok

Example 2

	
	: aa [ ' dup compile, ] ;

	see aa
	[0] DUP
	ok

Example 3

COMPILE,

becomes extremely useful when you only have an XT but you want to compile it into your word.

		:> "I am just an XT." . ; \ puts an XT on the stack
		ok
		: bb ( xt -- ) "What's this?" . [ compile, ] ;
		ok
		bb
		What's this? I am just an XT. ok

Quiz

Question 1

In Example 1, how would it change if you used

POSTPONE

instead of

[COMPILE]

? Explain and check your answer using

SEE

The word

postpone

pushes the XT of

HI

to the stack and runs

COMPILE,

, which takes the

HI

XT on the stack and compiles it into the enclosing word. However the program is not running within a word definition, hence there is an error.

Question 2

What are the compilation semantics of

HI

in Example 1? Is using

[COMPILE]

POSTPONE

of any value? Explain and check your answer using

SEE

Since it is not an immediate word, the compilation semantics of the word

HI

is to append its code section to the enclosing new word being defined. Hence the word

[compile]

is redundant.

Question 3

HI

were immediate, what would your answer to Question 2 be? Explain and check your answer with

SEE

HI

were immediate, its code section will be run instead of being compiled into the enclosing word.

[COMPILE]

POSTPONE

should then be used.

Question 4

What does

AA

in Example 2 do? Why did we have to use the switch mode operators?

AA

compiles the code of

DUP

into its definition. It is the same as

: aa dup ;

because

DUP

is not immediate. The switch mode operators is needed because

COMPILE,

is not immediate.

Question 5

Write

[COMPILE]

in terms of

COMPILE,

and other words you know except for

POSTPONE

		: [COMPILE] 
			' compile, 
		; immediate

Next: Application: Word Usage Counts