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IamRob
PostPosted: Thu Dec 17, 2020 6:40 pm 
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I am a little baffled by how IMMEDIATE works.

My understanding is that when a new word is created, and any word that is marked as IMMEDIATE will automatically execute during compiling.

Here is an example of my expectation of what IMMEDIATE should do.

: INVERSE F EMIT ; IMMEDIATE
: TEST INVERSE ;
OK

When TEST is being compiled, INVERSE should be executed and therefore OK should be printed in inverse text. But it doesn't.

Typing F EMIT at the prompt will put OK in inverse.
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GARTHWILSON
PostPosted: Thu Dec 17, 2020 9:11 pm 
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Should work. If you use SEE to view what got compiled in TEST, it should look like a do-nothing word, because F EMIT was executed rather than compiled.

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JimBoyd
PostPosted: Fri Dec 18, 2020 12:15 am 
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I noticed in your example that OK is on the next line. I don't know about the Apple but on the C64 a carriage return clears the reverse video.
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IamRob
PostPosted: Fri Dec 18, 2020 3:22 am 
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GARTHWILSON wrote:
Should work. If you use SEE to view what got compiled in TEST, it should look like a do-nothing word, because F EMIT was executed rather than compiled.


I am using an ITC Forth.
The indirect link for INVERSE got compiled. If I run TEST then it works and OK is in inverse.
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IamRob
PostPosted: Fri Dec 18, 2020 3:29 am 
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JimBoyd wrote:

I noticed in your example that OK is on the next line. I don't know about the Apple but on the C64 a carriage return clears the reverse video.


INVERSE stays on till it gets turned off with E EMIT which is the description for NORMAL.

: TEST INVERSE ." Hello World" NORMAL ;
OK
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GARTHWILSON
PostPosted: Fri Dec 18, 2020 4:13 am 
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IamRob wrote:
GARTHWILSON wrote:
Should work. If you use SEE to view what got compiled in TEST, it should look like a do-nothing word, because F EMIT was executed rather than compiled.

I am using an ITC Forth.
The indirect link for INVERSE got compiled. If I run TEST then it works and OK is in inverse.

So it sounds like COMPILER, which is called by INTERPRET if STATE is ON, is not looking up and responding to the IMMEDIATE bit in the header correctly. (It may be a bit different in your ITC Forth, but the result should be the same.)

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IamRob
PostPosted: Fri Dec 18, 2020 5:49 pm 
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Quote:
So it sounds like COMPILER, which is called by INTERPRET if STATE is ON, is not looking up and responding to the IMMEDIATE bit in the header correctly. (It may be a bit different in your ITC Forth, but the result should be the same.)[/color]


Ok. got it figured out.
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JimBoyd
PostPosted: Fri Dec 18, 2020 9:58 pm 
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GARTHWILSON wrote:

So it sounds like COMPILER, which is called by INTERPRET if STATE is ON, is not looking up and responding to the IMMEDIATE bit in the header correctly. (It may be a bit different in your ITC Forth, but the result should be the same.)


Fleet Forth's INTERPRET does not check the header, (FIND) does. (FIND) returns a tri-state flag. true (-1) if found and not immediate, one if immediate, and zero if not found. State is either TRUE (-1) or FALSE (0).
The only test INTERPRET does if it determines that a word is found is the following:
Code:
         STATE @ =
         IF
            ,
         ELSE
            EXECUTE
            ?STACK
         THEN
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IamRob
PostPosted: Sat Dec 19, 2020 12:57 am 
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Quote:
The only test INTERPRET does if it determines that a word is found is the following:
Code:
         STATE @ =
         IF
            ,
         ELSE
            EXECUTE
            ?STACK
         THEN

[/color]

The FIG interpreter has this for INTERPRET which checks the current STATE against a word's STATE. (which is part of the word length byte)

: INTERPRET -FIND IF STATE @ < IF CFA , ELSE CFA EXECUTE THEN ?STACK ELSE HERE NUMBER DPL @ 1+ IF [COMPILE] DLITERAL ELSE DROP [COMPILE] LITERAL THEN ?STACK THEN AGAIN ;

-FIND, when it finds a word, returns with the length byte, which also includes the IMMEDIATE bit and SMUDGE bit. The current STATE is set at $C0 and compared with the word length byte. A word's length byte has the hi-bit set for TRAVERSE, so the length byte will be at least $C0 plus the word length for an IMMEDIATE word (always > $C0). This is when the CFA EXECUTE happens in INTERPRET.
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JimBoyd
PostPosted: Sat Dec 19, 2020 10:02 pm 
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IamRob wrote:
Quote:
The only test INTERPRET does if it determines that a word is found is the following:
Code:
         STATE @ =
         IF
            ,
         ELSE
            EXECUTE
            ?STACK
         THEN


The FIG interpreter has this for INTERPRET which checks the current STATE against a word's STATE. (which is part of the word length byte)

: INTERPRET -FIND IF STATE @ < IF CFA , ELSE CFA EXECUTE THEN ?STACK ELSE HERE NUMBER DPL @ 1+ IF [COMPILE] DLITERAL ELSE DROP [COMPILE] LITERAL THEN ?STACK THEN AGAIN ;

-FIND, when it finds a word, returns with the length byte, which also includes the IMMEDIATE bit and SMUDGE bit. The current STATE is set at $C0 and compared with the word length byte. A word's length byte has the hi-bit set for TRAVERSE, so the length byte will be at least $C0 plus the word length for an IMMEDIATE word (always > $C0). This is when the CFA EXECUTE happens in INTERPRET.


The first Forth I used was 64Forth for the C64 which was a superset of FIG Forth. Fleet Forth is a Forth-83 Standard Forth. The Forth-83 standard does things a little differently. Rather than -FIND there is FIND . FIND takes the address of a counted string and returns the tri-state flag I already mentioned.
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JimBoyd
PostPosted: Sun Dec 20, 2020 8:46 pm 
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To be clear, the Forth-83 word FIND returns two items. Here is the stack effect for each type of result.
Code:
ADDR -- CFA  1   \ FOUND AND IMMEDIATE
ADDR -- CFA -1   \ FOUND AND NOT IMMEDIATE
ADDR -- ADDR 0   \ NOT FOUND
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IamRob
PostPosted: Mon Dec 21, 2020 5:32 pm 
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JimBoyd wrote:

To be clear, the Forth-83 word FIND returns two items. Here is the stack effect for each type of result.
Code:
ADDR -- CFA  1   \ FOUND AND IMMEDIATE
ADDR -- CFA -1   \ FOUND AND NOT IMMEDIATE
ADDR -- ADDR 0   \ NOT FOUND

I will have to keep track of how often -FIND is called when disassembling ProForth to see if it can benefit from this method. It definitely has possibilities, especially if it gets called often.
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