[Coco] Back to DEF FN

[Aaron Wolfe]

Extended Basic Unravelled contains a detailed disassembly of the DEF
code.  Here is the relevant bit:


1015 8880 BD B2 6A // JSR LB26A
    SYNTAX CHECK FOR '('

1016 8883 C6 80 // LDB #$80
   GET THE FLAG TO INDICATE ARRAY VARIABLE SEARCH DISABLE

1017 8885 D7 08  // STB ARYDIS
   AND SAVE IT IN THE ARRAY DISABLE FLAG

1018 8887 BD B3 57 // JSR LB357
   GET VARIABLE DESCRIPTOR

1019 888A 8D 25 // BSR L88B1
   'TM' ERROR IF STRING

1020 888C BD B2 67 // JSR LB267
   SYNTAX CHECK FOR ')'

As you can see, there is no loop or any other mechanism that might
allow more than a single variable to be parsed.
The docs might be inconsistent or confusing, but the code is clear.

-Aaron


On Mon, Jan 27, 2014 at 7:37 PM, Rogelio Perea <os9dude at gmail.com> wrote:
> Just got delivered a library copy of Peter Vernon's "Making The Mos of Your
> TRS-80 Color Computer", it was the bargain bin on Amazon (Prentice-Hall
> Australia 1983 ISBN 0 7248 0752 7).
>
> Leafing through the pages I came to the section where each ECB command is
> listed, an odd wording of the old DEF FN caught my eye:
>
> 10 DEF FN( A B C)=(A+B+C)/3
> 20 INPUT"ENTER THREE NUMBERS";A,B,C
> 30 D=FNA(A B C)
> 40 PRINT"THE AVERAGE IS";D
> 50 PRINT
> 60 GOTO 20
>
> I was perplexed for a bit. Could it be that the proper syntax on the CoCo's
> DEF FN requires the variables to be separated by a space instead of a
> comma? could it be *that* simple?
>
> I retyped the MOD routine into the CoCo as:
>
> 10 DEF FNRE=(N1 N2)=N1-INT(N1/N2)*N2
> 20 CLS
> 30 INPUT"NUMBER 1";N1
> 40 INPUT"NUMBER 2";N2
> 50 PRINT
> 60 PRINT N1;"MOD";N2;"IS";FNRE(N1 N2)
> 70 PRINT
> 80 GOTO 30
>
> And it worked. This routine above is based on one shown by Lewis
> Rosenfelder in "Basic Faster And Better & Other Mysteries" book. I was on a
> roll and ported another one from Rosenfelder's (date day # finder):
>
> 10 CLS
> 20 DEF FNJD(Y M
> D)=(M-1)*28+VAL(MID$("000303060811131619212426",(M-1)*2+1,2))-((M>2) AND
> ((Y AND NOT -4)=0))+D
> 30 INPUT"YEAR (1901-2099)";Y
> 40 INPUT"MONTH (1-12)";M
> 50 INPUT"DAY (1-31)";D
> 60 PRINT
> 70 PRINT"THAT IS THE";FNJD(Y M D);"DAY OF THE YEAR"
> 80 PRINT
> 90 END
>
> Still smiling as I type this. The CoCo ECB book sins in being sparse at
> best on covering one of the most underrated functions in the BASIC
> repertoire, one that can come useful if applied properly. It had been years
> (decades actually) since the first time I fiddled with DEF FN and it was
> disappointing back then that I could not get it to work with 2 or more
> arguments... I was using the syntax I knew from the TRS-80 Model I and III
> BASIC separating the arguments by commas.
>
> With all this, the CoCo's DEF FN is still limited to numeric functions as
> far as I know; ran a routine trying to define a string variable function
> (simple concatenation) and the CoCo returned a type mismatch error. Oh
> well, having this found to work with multiple variable arguments is in my
> eye *the* discovery of the 21st century. Old ECB CoCo style :-)
>
>
> -- RP
>
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