I’ve been learning OCaml for a compiler course, and while parsing s-expression I encountered the following scenario ... match (sexp_list : sexp list) with ... | Symbol(id)::rest when (id == keyword_add) -> (parse_binary Add ...) | Symbol(id)::rest when (id == keyword_sub) -> (parse_binary Sub ...) …

Just to be clear, adding computations to patterns is called active patterns . While it is possible to implement them in the language, their compilation will be very different. Right now, patterns are compiled into efficient decision trees, leveraging the fact that the pattern language is fully static…

My advice is to stay away from when clauses, unless you have a very good reason for it. In your case I would simply use a nested pattern matching: match sexp_list with | Symbol id :: rest -> begin match classify id with | Binary_op binop -> parse_binary binop rest | ... -> ... (* ha…

Thank you for your advice, that seems like the way to do it indeed. I’ll have to make up a new variant type for the return value of classify id, but it’s not too much work at all. I would also like to hear other people’s thoughts on this if possible:).

If your id has type string (or any other non-abstract data type), then you can match on it, e.g., match exps with | Symbol "add" :: rest -> parse_binary Add ... | ... if you think that hoisting binary and unary rules will benefit for you parser you can split them like this let rec parse_exps = f…

Thanks again for such prompt feedback! The reason I didn’t match on string literal is to avoid hard-coding them into my parser. Also, the reason I’m making unary/binary expression is that although I’m parsing S-Expression here, my target language requires these primitive arithmetic operations to b…

Thank you so much for your explanation:). This is really really helpful. I’m going to spend some time digesting all of this, and I’ll definitely look into BAP!

Declare variable and evaluate expression within pattern

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SkySkimmer January 16, 2020, 5:43pm 5

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Declare variable and evaluate expression within pattern

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