Question on extending List example

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Siberian

Joined: 09 Mar 2010
Posts: 14

Siberian 13 Mar 2010, 17:59

Hello, again.

This question concerns list example posted somewhere on this board. The main idea is redefining list constant each time new item is appended.
But is it possible to detect for any item if it is already contained in the list before appending it?
I was able to produce one implementation for items which are quoted strings (after studying includeonce example). But main interest is to do it with any item type - simple match doesn't help, or am I doing something wrong?

13 Mar 2010, 17:59

Siberian

Joined: 09 Mar 2010
Posts: 14

Siberian 13 Mar 2010, 18:24

Small example to explain what I have in mind:

Code:

macro ListContains item, flagVar {
     flar equ 0                    
      match item,             list \{ flagVar equ 1 \}
        match item tail,        list \{ flagVar equ 1 \}
        match head item,        list \{ flagVar equ 1 \}
        match head item tail,   list \{ flagVar equ 1 \}
}

; case 1
list equ '1', '2', '4', '5'

ListContains '2', flag           ; flag equ 1 - correct
ListContains '3', flag              ; flag equ 0 - correct
ListContains '5', flag              ; flag equ 1 - correct
ListContains 'junk', flag   ; flag equ 0 - correct

; case 2
list  equ     1, 2, 4, 5

ListContains 2, flag          ; flag equ 1 - correct
ListContains 3, flag          ; flag equ 1 - incorrect
ListContains 5, flag                ; flag equ 1 - correct
ListContains junk, flag               ; flag equ 1 - incorrect

Basically, every macro match in second case evaluates. I'm aware of the reason, but is there a way to implement the solution for non quoted items in the list?

13 Mar 2010, 18:24

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr 13 Mar 2010, 19:47

Siberian,

match =0, 0 {…} works as expected. You may find irp useful to iterate through list items too.

13 Mar 2010, 19:47

Siberian

Joined: 09 Mar 2010
Posts: 14

Siberian 13 Mar 2010, 20:10

It really works!

Thanks, baldr.

I don't know why, but I thought that expression at "=" sign within a match pattern will be always treated as direct value to compare with. But I guess macro argument is dereferenced in that case as well.

13 Mar 2010, 20:10

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr 13 Mar 2010, 20:27

Siberian,

You're right, that's the way macro parameters work. «=» is a match feature, not macro's.

Be careful: match 1,0 { db 1 } could surprise you. Wink

13 Mar 2010, 20:27

Borsuc

Joined: 29 Dec 2005
Posts: 2465
Location: Bucharest, Romania

Borsuc 14 Mar 2010, 13:36

restore the flagVar so it doesn't create unexpected bugs. Also you can use "define flagVar +" for the 'not found' signal and "define flagVar" (empty) for the 'found' signal, if you want.

But you have to restore it in each of the 4 matches (before defining), AND at the end of the macro.

14 Mar 2010, 13:36

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr 14 Mar 2010, 14:01

Borsuc,

Something like this?

Code:

struc reequ [val] {
common
  restore .
  . equ val
}

macro ListContains item, contains {
  contains equ 0
  match l, list \{
    irp i, l \\{
      match =item,i \\\{ contains reequ 1 \\\}
    \\}
  \}
}

list    equ     1, 2, 4, 5

ListContains 2, flag            ; flag equ 1 - correct
display "0"+flag
ListContains 3, flag            ; flag equ 1 - incorrect
display "0"+flag
ListContains 5, flag            ; flag equ 1 - correct
display "0"+flag
ListContains junk, flag         ; flag equ 1 - incorrect
display "0"+flag

Adding restore contains before contains equ 0 has its pros and cons. At the end of ListContains macro it will destroy returned value.

14 Mar 2010, 14:01

Borsuc

Joined: 29 Dec 2005
Posts: 2465
Location: Bucharest, Romania

Borsuc 14 Mar 2010, 14:23

Yes that's the idea, but...

baldr wrote:

Adding restore contains before contains equ 0 has its pros and cons. At the end of ListContains macro it will destroy returned value.

you add it at the end of the macro, not at the beginning. after the matches.

HOWEVER you do NOT add it in THIS particular case because you use the flag OUTSIDE the macro -- if you only used it INSIDE the macro, then you should restore it... but here it is not needed to do it at the end of the matches. Wink

I'm only saying this because I had some annoying bugs come out of it, "leaking" variables and stuff. took me a while to figure out. Sad

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Previously known as The_Grey_Beast

14 Mar 2010, 14:23

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