Re: How do you create a grammar for a multi-language language?

On Sunday, March 6, 2022 at 9:06:34 AM UTC-8, Christopher F Clark wrote:


(snip)


> However, you are actually solving a "simpler" problem. And, the
> standard approach to that is to embed the second language as a
> "string" in the outer language. Many languages (and their
> compilers/interpreters) do that. That's exactly what your XSLT case
> does. The XPATH code is simply a string in the XSLT language, and the
> XSLT language doesn't attempt to parse it. It simply hands the code
> off to an XPATH parser when in knows the string is XPATH code.


That works when the outer language is parsed first.


For PHP, and I believe the C preprocessor, the inner language is parsed
first, so the parser has to ignore everything, including quoting, in
the outer language.


I don't believe I ever tried preprocessor statements inside C string
constants, but as far as I know, it works.


One has to be careful to avoid ambiguities between the two,
or are created with the combination of the two languages.
[PHP effectively treats material between ?> and <?php as an instruction
to print the material as if it were a quoted string.


C says that the input is tokenized before it does the preprocessor
phase, so it does not look inside quoted strings. The # and ##
preprocessor operators allow some preprocessor time creation of quoted
strings. -John]

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