appropriate to build an ast using nom?

[mspiegel]

I was trying to adapt the arithmetic.rs example and have the parser generate an AST rather than compute the result. I am very new to rust and was getting tripped up. When I am creating new values of the AST enum I think I needed to use the try! macro but I wasn't sure how to combine that with the nom macros. Is nom a good use case for generating the ASTs?

[mspiegel]

I'm going to make another attempt to write this in the next few days. I think I know what mistakes I made in the first attempt.

[Geal]

Hi! Any reason you closed this issue? Did you find a way to generate an AST? I'm sorry I can't answer fast, I'm currently traveling.

[mspiegel]

Thanks! I closed the ticket because I wasn't sure if reporting my question as an issue was the appropriate forum. In any event I've made some progress in a branch: https://github.com/mspiegel/nom/blob/arithmetic_ast/tests/arithmetic_ast.rs. The downside is that in a few instances I have to clone the entire AST which I suspect is not the right way to do it. See for example, https://github.com/mspiegel/nom/blob/arithmetic_ast/tests/arithmetic_ast.rs#L75. Whenever you have the chance any help would be 1000% appreciated.

Once I get this AST calculator working I was planning on applying the same strategy to submit a pull request for ehuss/license-exprs#3

[mspiegel]

Yup I'm very stuck about how to rewrite my initial version without relying on clone. I think there are two problems but my knowledge of rust is very poor so there may be N problems for any value of N. One problem is that I can't assign "expr" to a new Expr value that is constructed out of the old "expr" reference. The other problem is that the Expr gets moved into the closure because it's not copyable so then I can't return "acc" on line https://github.com/mspiegel/nom/blob/arithmetic_ast/tests/arithmetic_ast.rs#L79. I've tried playing around with Expr, Box, RefCell, unsafe, I couldn't get a working solution.

[mspiegel]

Aha wait I had an insight. Instead of trying to modifying the Expr while parsing, I should be appending some things onto a vector while consuming the input and then in the return closure I can build the final Expr using the vector. I will try that tomorrow morning. Sorry for the comment spam.

[mspiegel]

Success!!!!!!! I'll submit a pull request.