ARexx - compound substitution test

[solarmon]

Hi,

Another hurdle in my ARexx journey....

I've been learning about ARexx's use of compound variables. I was actually looking/hoping for list/array type structures as in other languages.

I'm aware of the way that ARexx does variable substitution and was hoping to make use of this.

However, this bit of test code has me confused as to why it does not work in the way I think/expect it to work.

The test code is below:

/* Compound subtitution test */
test.blue = 1

keyword = "blue"

say "keyword:" keyword
say "test.keyword:" test.keyword
say "test.blue:" test.blue
say ""

if test.keyword == 1 then
	say keyword "exists"
else
	say keyword "does not exist"

And I would expect the end result to be:

blue exists

since I am expecting:

TEST.blue == 1

There seems to be some kind of substitution since 'keyword' is replace with 'blue' on the output results. But the test for "test.keyword == 1" does not seem to work the way I think/expect it to work. I'm expecting this to be 'true' since the compound variable test.blue is set to 1.

Can anybody tell me what I'm doing wrong, or whether I've mistunderstood how compounds and subsitution works in ARexx/Rexx?

Cheers!

[thomas]

Every word behind the dot is considered a variable and substituted by its value.

test.blue = 1

in this instruction blue is replaced by the value of the variable blue. As this variable has not been set before, its value is its name in upper case letters. This means the instruction actually is

test.BLUE = 1

now you set the variable keyword to the value "blue" in lower case letters. So test.keyword is "test.blue", but this is different from test.BLUE. Case matters.

[solarmon]

Originally Posted by thomas

Every word behind the dot is considered a variable and substituted by its value.

test.blue = 1

in this instruction blue is replaced by the value of the variable blue. As this variable has not been set before, its value is its name in upper case letters. This means the instruction actually is

test.BLUE = 1

now you set the variable keyword to the value "blue" in lower case letters. So test.keyword is "test.blue", but this is different from test.BLUE. Case matters.

Thanks for the response. I understand your explanation and, indeed, if I change keyword to 'BLUE' it matches.


However, then this means I cannot use this method to check if a non integer 'index' exists.

I was hoping use this method to create a list of 'words' and check with that word exists in the list.

For example, a list of colours:

('red', 'green', 'blue')

And I want to check whether the text/string 'blue' (or any other colour) is in this list.

I know I can do it by creating a compound 'list' using numbered 'indexes', for example:

colour.0 = 3
colour.1 = "red"
colour.2 = "green"
colour.3 = "blue"

keyword = "blue"

exists = 0
do i = 1 to colour.0
	if colour.i == keyword then
		exists = 1
end	

if exists then
	say "Colour" keyword "is in list"
else
	say "Colour" keyword "is not in list"

But the problems I see/have with this method is that:

1. You need to increment the index when creating the list.
2. You need to iterate through the compound list.
3. You need to specify and know the size/number of items.

Rexx/ARexx just don't seem to have a user friendly 'associative' array. This basically sums up with I'm looking for and the issues I have with it:

https://stackoverflow.com/questions/...arrays-in-rexx

I get it being case sensitive, but what I don't understand/get is it changing uninitialised variables to UPPERCASE.

I thought the Symbol() function might be a to check if a variable has been set, but some quick tests showed some 'funny' results depending on what case you give it.

[thomas]

Originally Posted by solarmon

However, then this means I cannot use this method to check if a non integer 'index' exists.

Yes, you can. Just be aware that the index is case sensitive.

instead of

test.blue = 1

use

x = "blue"; text.x = 1

You can even do

blue = "blue"; test.blue = 1


Or in your new example you could initialise the index like this:

test. = 0
do i=1 to colour.0
   colour = colour.i
   test.colour = 1
end

[solarmon]

@thomas,

Thanks. I understand your example and have tested it and it does work.

However, it is not that 'easy' to use - for the beginner. It may be OK for relatively small static lists, but not so easy for larger, and dynamically generated, lists.

I appreciate your help, and my knowledge of ARexx has improved a bit more!

Cheers!

[idrougge]

I think it works much better for dynamically generated lists than for small and static lists, as can be seen above. Dynamically generated lists will generally be "indexed" by variables and not by symbols typed into the script.

[solarmon]

Originally Posted by idrougge

I think it works much better for dynamically generated lists than for small and static lists, as can be seen above. Dynamically generated lists will generally be "indexed" by variables and not by symbols typed into the script.

Maybe it is just my lack of understanding of the ARexx language, but these are challenges facing me at the moment, as a beginner. I don't want to jump through hoops to just use 'lists' and 'arrays'.

[Ami]

RosettaCode has good amount of search/sort algorithms examples written in REXX - https://rosettacode.org/wiki/Category:REXX

https://rosettacode.org/wiki/Search_a_list#REXX
https://rosettacode.org/wiki/Search_...f_records#REXX

[idrougge]

Originally Posted by solarmon

Maybe it is just my lack of understanding of the ARexx language, but these are challenges facing me at the moment, as a beginner. I don't want to jump through hoops to just use 'lists' and 'arrays'.

Sorry, you don't have "lists" or "arrays". No such thing. Learn to live without them or fake them.

In many cases, QUEUE, PUSH and PULL can be used as a substitute for lists, as long as your list is not too long.

Originally Posted by Ami

RosettaCode has good amount of search/sort algorithms examples written in REXX - https://rosettacode.org/wiki/Category:REXX

Unfortunately, most REXX examples on Rosettacode were written by a lunatic with a… "special" coding style.

[Daedalus]

Originally Posted by solarmon

I get it being case sensitive, but what I don't understand/get is it changing uninitialised variables to UPPERCASE.

That's an ARexx quirk: it's case-sensitive, but also converts everything that isn't in quotes to uppercase internally - strings, variable names, keywords, commands... That's why almost all commands and port names for almost any program are given in capitals, because that removes some of the case-sensitivity and makes quote requirements more flexible. For example:

address workbench

works, as do

ADDRESS WORKBENCH

and

ADDRESS "WORKBENCH"

However,

address "Workbench"

won't find the WORKBENCH port, since putting the string in quotes means it's no longer converted to uppercase internally. Many examples use uppercase for much of the script for these reasons - it's a way to tell which parts were intended to be uppercase and which should be in quotes.

With that in mind, things might be simpler to visualise if you use all upper-case variable names, at least to start with.

Just bear in mind that any variable that isn't initialised is just a string, and because it's not in quotes, it's converted to uppercase.

Symbol() is probably giving you funny results because of the case too - since you're giving it a string (presumably in quotes), the case has to match, and as has been pointed out, the variable name is actually uppercase internally.

I like ARexx, but I also think in some ways it's quite different conceptually from other common languages. Once you start to get a feel for the different ways of doing things, it will make a lot more sense.