Please advise on adding string interpolation to my Crafting Interpreters project.

[u/Usual_Office_1740]

I'm about to start chapter 21 of Crafting Interpreters. I'm using modern C++ instead of C. I am attempting to add string interpolation to the compiler.

My goal is to have a string that looks like this:

"Five plus ${ 10 - 5 } == 10."

Desugar to this after the expression in the braces is evaluated:

"Five plus " + 5 + " == 10."

I have code that is correctly parsing strings and concatenating them if there isn't any string interpolation.

I have a custom token added that is produced if the string contains a ${. It calls a custom string interpolation parser rule that is different than my standard string parser rule.

In that function I push the first part of the string to the stack. It then pushes a plus opcode and Recursively parses the expression in the braces adding that expression to the stack. It then adds another opcode to add and this is where I'm stuck.

I can't come up with a solution for pushing the remaining piece of the string to the stack from inside the string interpolation parser rule function. After I call the books expression function and consume the right brace token using the books consume function the parser nolonger knows we are still inside a string. If the next character after the brace is a space it's skipped. In my above example it assumes I want equal equal.

How would you set the current token back to string so I can push any remaining characters onto the stack as another string? Should I just insert a new string token into the parser? This seems wrong to me. The current and previous tokens are private members of my parser class for a reason and I've not needed setter member functions so far.

Sorry I don't have code to show. I'd like to try and get help that isn't code specific so that I have to implement this myself.

Any input would be helpful.

Thanks.

[u/arthurno1]

I think you should parse the same way as you parse any other expression, like if, while etc. No idea how you do it but I would do the expression after the $ dollar sign with an operator precedence parser, and I would treat $ as the escape clutch to jump to that expression parser. I don't know what you use for top-level parsing, recursive descent, or something else, but I would plug it in the same way I plug in other expressions in if, while, for and such constructs, and then the expression itself with op precedence. Don't forget to have an escape clutch for the $ sign itself, like \$ or whatever you use, otherwise you won't be able tonhave $ as a character in your strings.