So my current code has a procedural macro that is interpreting this algebraic expression as a function this is the error error: expected expression, found keyword `fn` –> src\main.rs:5:5 | 5 | symbolic!(x^2 + 2*x) | ^^^^^^^^^^^^^^^^^^^^ expected expression | = note: this error originates in the macro `symbolic` (in Nightly builds, run with -Z… Read More Why is this procedural macro interpreting this expression as a function?