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Unusual AREXX behaviour / AREXX bug
Quite a regular
Quite a regular


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Perhaps this is a documented feature, but I have no idea why this is happening. Here's an example script:

/**/
Test="1"
Test2=Translate(Test,"01","10")
SAY Test2
SAY 0+Test2
Exit

What would you expect to be output on the shell?

0
0

Obviously. And that's exactly what happens.

But add one line to the script like so:

/**/
Test="1"
SomeUnusedVar=Test+26
Test2=Translate(Test,"01","10")
SAY Test2
SAY 0+Test2
Exit

What now? It outputs:

0
1

Why's that? If I use DataType() to check Test2, it's a number, and that number is 0. 0 plus 0 should be 0.

Edit: Thread title change to make it easier for me to find in the future.


Edited by MickJT on 2017/10/16 8:01:48
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Re: Unusual AREXX behaviour
Amigans Defender
Amigans Defender


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@MickJT

Does it do the same if you remove the double quotes from your original Test assignment?

ie.
Test=1



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Re: Unusual AREXX behaviour
Quite a regular
Quite a regular


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Yes, it does.

I have tested this on Regina REXX as well, and the 2nd example prints 0 both times as expected, even with AREXX_BIFS & AREXX_SEMANTICS enabled.

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Re: Unusual AREXX behaviour
Quite a regular
Quite a regular


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This also causes the same issue:

/**/
Test=1
IF Test=1 THEN NOP /* Or any DO ... END statement */
Test2=Translate(Test,"01","10")
SAY Test2
SAY 0+Test2
Exit

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Re: Unusual AREXX behaviour
Just can't stay away
Just can't stay away


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Probably because Translate() returns a string and the "+" is fooled.
This code:
/**/
Test="1"
Test2=Translate(Test,"01","10")
say datatype(Test)
say datatype(Tes2)

will output:
NUM
CHAR

And if you add Trunc() to your original code, like:
Test2=Trunc(Translate(Test,"01","10"))
you have the expected behaviour.

Philippe 'Elwood' FERRUCCI
Sam460ex 1.10 Ghz
http://elwoodb.free.fr
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Re: Unusual AREXX behaviour
Quite a regular
Quite a regular


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@Elwood

Look at the two examples in the very first post, and notice that the only difference is adding SomeUnusedVar=Test+26 (or an IF statement using the Test variable).

At the bottom of the first post I also noted that I checked with DataType() already to verify that the Test2 variable is NUM.

The reason your example outputs CHAR is because of a typo. The variable "Tes2" does not exist. Test2 is NUM.

If I use Trunc, I get 1 and 1 as the output if I add an IF statement that shouldn't do anything.

/**/
Test=1
IF Test=1 THEN NOP /* Or any DO ... END statement */
Test2=Trunc(Translate(Test,"01","10"))
SAY Test2
SAY 0+Test2
Exit

Output:

1
1

The output from Trunc is 1 when it should be 0 (the Translate function swaps 1 to 0). If I remove IF Test=1 THEN NOP, a line which shouldn't do anything, then I get the expected output of 0 and 0.

Edit: Corrections.


Edited by MickJT on 2017/4/25 19:29:16
Edited by MickJT on 2017/4/25 19:30:17
Edited by MickJT on 2017/4/25 21:07:21
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Re: Unusual AREXX behaviour
Just can't stay away
Just can't stay away


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Oops, you're right.

I just tested in OS3.9 in E-UAE and I still have the same wrong output with the original code:
0
1

so this behaviour/bug is here since day one.

Philippe 'Elwood' FERRUCCI
Sam460ex 1.10 Ghz
http://elwoodb.free.fr
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Re: Unusual AREXX behaviour
Quite a regular
Quite a regular


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Yeah, it's strange. I wanted to use SubStr() and if a particular user setting was 0, it would need to read one more byte. My way which I thought was clever was to just use Translate() to swap 0 and 1 around. For example: Test=SubStr(Output,Length+Translate(Setting,"01","10"))

That works unless the Setting variable has been checked with IF in the past.

I could rename the setting to do its opposite and then avoid using Translate(), but it wouldn't be as intuitive. Easy enough to work around though.

Thanks for testing it with OS3.9. I hadn't tried that.

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Re: Unusual AREXX behaviour
Not too shy to talk
Not too shy to talk


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If Setting is always 0 or 1 you could use 1-Setting to swap it.

Length + 1 - Setting makes more sense anyway IMHO because it needs to translate between string and number only once.


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Re: Unusual AREXX behaviour
Quite a regular
Quite a regular


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I knew someone would think of a better way. Thanks thomas.

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Re: Unusual AREXX behaviour
Just can't stay away
Just can't stay away


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if you want to use the variable to hold the number of iterations as well you can use:

/**/
do 1 to 10
  
if x//2 = 0 then do:
    
say x " is even"
  
else
    
say x " is odd"
  
endif
end


the remainder (//) when divided by two will always return 0 or 1, problem solved


Edited by Severin on 2017/4/27 1:26:09
Edited by Severin on 2017/4/27 1:29:11
Edited by Severin on 2017/4/27 1:32:05
Amiga user since 1985
AOS4, A-EON, IBrowse & Alinea Betatester

Ps. I hate the new amigans website. <shudder>
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