Declarative representation of a file path with embedded environment variables - environment-variables

Question

I am looking at a situation where I'd like to bring some structure to what would be a string in an typical language. And wondering how to use Rebol's parts box to do it.
So let's say I've got a line that looks like this in the original language I'm trying to dialect:
something = ("/foo/mumble" "/foo/${BAR}/baz")
I want to use Rebol's primitives, so certainly a file path. Here is a random example of what I thought of off the top of my head:
something: [%/foo/mumble [%/foo/ BAR %/baz]]
If it were code you'd use REJOIN or COMBINE. But this is not designed to be executed, it's more like a configuration file. You're not supposed to be running arbitrary code, just getting a list of files.
I'm not sure about how feasible it is to stick with strings and yet still have these type as FILE!. Not all characters work in a FILE!, for instance:
>> load "%/foo/${BAR}/baz"
== [%/foo/$ "BAR" /baz]
It makes me wonder what my options are in Rebol data that's supposed to represent a configuration file. I can use plain old strings and do substitutions like other things do. Maybe REWORD with an OBJECT block to represent the environment?
What is the 'reword' function in Rebol and how do I use it?
In any case, I want to know how to represent a filename in a declarative context with environment variable substitutions like this.

Answer 1

I should use file! Your example need "" after %
f: load {%"/foo/${BAR}/baz"}
replace f "${BAR}" "MYVALUE" ;== %/foo/MYVALUE/baz

Answer 2

you could use path! with parens.
the only issue is the root, for which you can use another character to replace the "%" used for files... let's use '! (note this should be a word 'valid character).
when calling to-block on a path! type, it returns each part as its own token... useful.
to-block '!/path/(foo)/file.txt
== [! path (foo) file.txt]
here is a little script which loads three paths and uses parens as a constructed part of the path and uses tags to escape path-illegal characters (like a space!)
environments: make object! [
foo: "FU"
bar: "BR"
]
paths: [
!/path/(foo)/file.txt
!/root/<escape weird chars $>/(bar ".txt")
!/("__" foo)/path/(bar)
]
parse paths [
some [
(print "------" )
set data path! here: ( insert/only here to-block data to-block data )
(out-path: copy %"" )
into [
path-parts: (?? path-parts)
'!
some [
[ set data [word! | tag! | number!] (
append out-path rejoin ["/" to-string data]
)]
|
into [
( append out-path "/")
some [
set data word! ( append out-path rejoin [to-string get in environments data] )
| set data skip ( append out-path rejoin [ to-string data])
]
]
| here: set data skip (to-error rejoin ["invalid path token (" type? data ") here: " mold here])
]
]
(?? out-path)
]
]
Note this works both in Rebol3 and Rebol2
output is as follows:
------
path-parts: [! path (foo) file.txt]
out-path: %/path/FU/file.txt
------
path-parts: [! root <escape weird chars $> (bar ".txt")]
out-path: %/root/escape%20weird%20chars%20$/BR.txt
------
path-parts: [! ("__" foo) path (bar)]
out-path: %/__FU/path/BR
------