On 21/06/2020 13:38, Bob Spelten via Ql-Users wrote:
Op Sun, 21 Jun 2020 09:46:23 +0200 schreef Norman Dunbar via Ql-Users <ql-users@lists.q-v-d.com>:

I have a vague recollection that Simon N Goodwin did something similar, maybe, in the DIY Toolkit.

I think it was passed a variable and a list of strings, and returned the position of the variable in the list. Something like that.

Maybe useful?

That would then be the PICK$ function.
It's on DIY disk 1, sub E, found on Dilwyn's site, where else?
To me it looks like PICK$ is the OPPOSITE of string SELect. PICK$ goes like this:

direction$ = PICK$(direction%,"North","East","South","West")

Which is nothing other than what we've already got, ie:

SELect on direction%
 = 1: direction$ = "North"
 = 2: direction$ = "East"
 = 3: direction$ = "South"
 = 4: direction$ = "West"
 = REMAINDER: direction$ = "???"

although it is theoretically faster than SELect as it calculates the location of the desired value rather than doing a bunch of comparisons.

But what a string select is supposed to do is:

direction% = PICK%(direction$,"North","East","South","West")

ie it returns some processable answer to a string query, viz

SELect on direction$
 = 'North': Go_to_North
 = 'East': Go_to_East
 = 'South': Go_to_South
 = 'West: Go_to_West
 = REMAINDER: Go_to_Hell

Just for fun, after reading Giorgio's mail, I went and wrote a function like PICK% (not PICK$). Although it is very simple, it is significantly slower than the INSTR suggestion I made earlier. It would probably more or less match a real string select in speed.

A hash function could be faster/more efficient for lists critical enough to justify the presence of such a function.

Ideally, it would be some function that would map lexicographical values well onto numbers, eg

f('ABC') < f('abc') or f('abcd') > f('abc'), etc, in a word or longword. Then things like ranges might be possible:

term = Magic(term$)
SELect on term
 = $00000123 TO $00000300: Go_to_North
 = $00003001, $00001234: Go_to_East
 = etc

though of what practical use they would be I know not..

But out of interest, does such a function exist?


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