I'm writing a syntax file for a string template DSL (somewhat similar to
Bash parameter expansion) which distinguishes between (a) `$(...)` (call it
"placeholder") and (b) `(...)` (call it "parens") where placeholder is
preferably an Operator and parens is preferably a String where the
parentheses themselves are Special, and where placeholders can occur inside
non-highlighted text and both can be nested inside (certain parts of)
placeholders and inside parens which are inside a placeholder.
I know that Vim regex do not support recursive patterns but I'm pretty
confident that this can be pulled off in a syntax definition using regions
which contain other regions, but I'm not quite sure if/how. I'm wondering
if someone can tell or point me to a relevant example. In particular I'm
not sure how/if you can nest a region with some delimiters inside another
region with the same delimiters without failing to match the outer closing
delimiter or matching past it.
In Perl 5.10+ it corresponds to a regex like this (in lieu of a formal
syntax), with the `\(` and `\)` which are part of the syntax replaced with
`\{` and `\}` for clarity, and each `$foo` representing some more or less
complicated subexpression whose exact shape is (I think) irrelevant to the
recursion issue. Thus this is not the actual regex used to match a
placeholder, but it is like an MWE which illustrates how it is supposed to
work.
``````perl
my $placeholder_re = qr{
(?<placeholder>
\$\{
$varname_re
(?:
$operator_A_re
(?<parens>
\s*
\{
(?<content>
(?:
[^\{\}\$]++
| \$ (?! \{ )
| (?&placeholder)
| (?&parens)
)*?
)
\}
\s*
)
$operator_B_re
(?<parens_B> (?&parens) )
|
$some_operator_re
(?<content_B> (?&parens) | (?&content) )
)
\}
)
}msx;
``````
TIA,
/bpj
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