[Coco] Back to DEF FN

[Aaron Wolfe]

There is a bit flag for each variable entry that indicates whether it
is a DEF variable.  I believe this means scalar P in BASIC is not the
same variable as P in the DEF function.  Somebody more familiar might
know for sure.

On Tue, Jan 28, 2014 at 1:29 PM, Arthur Flexser <flexser at fiu.edu> wrote:
> Well, this raises the more general question of what happens if a dummy
> argument used in a function definition has the same name as a scalar
> variable used by the program.  For example:
>
> 10 DEF FN(P) = P+3
>
> 20 P=20
>
> 30 Z=FN(5)
>
> The value of Z should now be 8, but what is now the value of P?  Is it
> still 20, or has it changed to 5?
>
> Art
>
>
>
> On Tue, Jan 28, 2014 at 1:14 PM, Aaron Wolfe <aawolfe at gmail.com> wrote:
>
>> There are two tables of variables in BASIC as William mentioned.  One
>> holds scalars, one holds arrays.  The ARYDIS flag causes the variable
>> lookup routine to simply skip the table of arrays when looking for a
>> match to the input variable name.  In the DEF FN case, this
>> effectively prevents arrays from ever being used as the variable
>> argument.  In your example the DEF FN(B) would always refer to the
>> scalar B, never the array B.
>>
>> On Tue, Jan 28, 2014 at 12:49 PM, Arthur Flexser <flexser at fiu.edu> wrote:
>> > Aaron, what does that "array search disable" do?   I'm guessing that if
>> you
>> > define FN(B)=B+3, that the array search disable means it makes no
>> > difference if the dummy variable B happens to be the name of a declared
>> > array or not.  Is that correct?
>> >
>> > Art
>> >
>> >
>> > On Tue, Jan 28, 2014 at 12:29 PM, Aaron Wolfe <aawolfe at gmail.com> wrote:
>> >
>> >> 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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>> >>
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