So now there is INTERPOLATE.
>> num: 1000
>> interpolate "Hello (num + 20) World!"
== "Hello 1020 World!"
It's the "bad boy" environment-capturing primitive, that does what most natives should avoid--sniffing the evaluator's concept of "current context" and reacting to that. (You usually don't want functions to be doing this, they should be reacting solely to their parameters.)
Besides capturing the context, it's a synonym for if you'd written compose2 @() .... COMPOSE2 is what you want use to change the delimiters or do other customizations... just use an @list form to capture the binding and tell COMPOSE2 you want to use the binding of that list:
>> num: 1000
>> compose2 @{{}} "Hello {{num + 20}} World!"
== "Hello 1020 World!"
Taking INTERPOLATE Stratospheric
One of the first things I did was fix the historical behavior of URL!
rebol2>> load "http://(domain)/example.txt"
== [http:// (domain) /example.txt]
So URL! now matches parentheses:
>> rev: 'info.rebol.forum
>> url: https://(reverse of rev)/t/usefulness-of-string-interpolation/2114
>> interpolate url
== https://rebol.metaeducation.com/t/usefulness-of-string-interpolation/2114
That works now, but I also plan to adjust the scanner to let you put parentheses or other delimiters before the :// ...
>> url: transcode "[protocol]://example.com"
== [protocol]://example.com
>> protocol: 'https
>> compose2 $[] url
== https://example.com
This made me realize that my dreams of giving FILE! "teeth" may be actualizable... INTERPOLATE can have special behavior if what you're working with is a file.
What I've always wanted to enforce is that if you put FILE! into FILE! where a slash is, that the thing you put in has a slash:
>> some-dir: %home/
>> interpolate %(some-dir)/something.txt
== %home/something.txt
>> interpolate %(bad-dir)something.txt
** Error: FILE! interpolation slash calculus mismatch: %home/
>> bad-dir: %home ; no slash, not a dir
>> interpolate %(bad-dir)/something.txt
** Error: FILE! interpolation slash calculus mismatch: %home
>> interpolate %(bad-dir)-something.txt
== home-something.txt
The idea is that you know from the template whether you're introducing a directory or not. This is all to bring sanity to the process--if you don't want sanity, use a plain string and turn it into a FILE! later. I just want "sanity out of the box".
The same rules would apply to PATH! if you're using them as a proxy for files:
>> path-dir: 'home/
>> interpolate %(path-dir)/something.txt
== %home/something.txt
>> interpolate %(path-dir)/something.txt
** Error: FILE! interpolation slash calculus mismatch: home/
I don't know that it would apply to WORD! substitutions, as they are kind of another beast. They can't have internal slashes so they don't have the same kinds of problems, so this is probably legal:
>> word-dir: 'home
>> interpolate %(word-dir)/something.txt
== %home/something.txt
I think TEXT! could similarly duck the rules, as long as it didn't have any internal slashes in the substitution:
>> text-dir: "home"
>> interpolate %(text-dir)/something.txt
== %home/something.txt
>> text-dir: "home/hostilefork"
>> interpolate %(text-dir)/something.txt
** Error: FILE! interpolation slash calculus mismatch: home/hostilefork
>> text-dir: "home/hostilefork/"
>> interpolate %(text-dir)/something.txt
== home/hostilefork/something.txt
Default TAG! Scanning Needs "Supertag"
Historical Rebol/Red tag doesn't enter a paired scan mode when it sees parentheses and such:
red>> tag: <foo=(1 > 2) bar=(3 < 4)>
*** Syntax Error: (line 1) missing ( at ) bar=(3 < 4)>
It thinks the first tag is <foo=(1 > and gets confused after that.
When I first was giving feedback on the design of Rebol/Red I proposed something I called SuperTag!, which people didn't seem to like but only Ladislav remarked on it, without defending the objection:
SuperTAG!: upon a " { ( [ < in tag content, validate substring via Rebol lexer · Issue #2234 · metaeducation/rebol-issues · GitHub
Given my proposal that PRINT be cued by TAG! to do interpolation, I think we should indeed make SuperTag the default:
>> print <Supertag should be the (if 2 > 1 [reverse "tluafed"])!>
Supertag should be the default!
But only if you are using the basic no dashes delimiter form of tag. That means you can still make weird tags, you just have to use -<...>-.
>> <)))>
** Error: Unexpected ) in TAG! scanning (use -<...>- if intentional)
>> -<)))>-
== -<)))>-
This gives me pause to wonder if we should also make SuperString the default (?)
>> "}}}"
** Error: Unexpected } in TEXT! scanning (use -"..."- if intentional)
You'd then be able to use strings inside escapes:
>> interpolate "You could do cool (reverse "ffuts")!"
You could do cool stuff!
It would make literals for delimiters longer than we'd like. You already can't use things like #[ as a character constant, but have to say #"[", so it's usually preferred to say "[", but now you'd have to say -"["- which is 5 characters to get 1.
But I've been thinking maybe we should let #[ and #} be character literals, and sacrifice the #[...] "construction syntax" and the #{...} for BINARY!. It's very speculative and requires a bit of a perception change, but it may be a better idea than it seems on the surface.
Crazy Fun Times
This is introducing some constraints on the types. But without constraints and just saying "oh, they're just arbitrary strings" then you can't get that much leverage.
philosophy : "Freedom To" and "Freedom From" in Software Architecture
If you want an arbitrary string, use TEXT!.
As with the -<...>- tag form, there can be workarounds for the "putting anything you want" syntaxes.