PIL analyzer doesn't like when a lambda parameter has the same name as a column in the outer scope

[lvella]

Consider this Powdr-ASM code, in a function body:

        // Apply S-box
        let x3 = array::map(step_a, constr |x| { let x3; x3 = x * x * x; x3});
        let x7 = array::zip(x3, step_a, constr |x3, x| { let x7; x7 = x3 * x3 * x; x7 });

It fails with:

thread 'poseidon2_bb_test' panicked at pil-analyzer/src/expression_processor.rs:257:13:
Variable already defined: x3
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

But if I change x3 to x_3 in the second lambda:

        // Apply S-box
        let x3 = array::map(step_a, constr |x| { let x3; x3 = x * x * x; x3});
        let x7 = array::zip(x3, step_a, constr |x_3, x| { let x7; x7 = x_3 * x_3 * x; x7 });

the error is avoided.

[chriseth]

We could consider allowing point 5 in https://github.com/powdr-labs/powdr/issues/1227 again. Any opinions?

[lvella]

My opinion is that our language is too similar to Rust, and too heavily reliant on lambda functions to not allow reuse of identifiers across different scopes.

[lvella]

In terms of issue #1227, I think 4, 5 and 6 should be allowed, and wouldn't mind 3 either.

[chriseth]

Let's allow 5!