LYR-SEM0189

a macro expanded in its own module

error · spec 11-metaprogramming

A site name!(…) or @name stands in the module that declares the macro.

Explanation

A macro expands in the modules that import it. Its own module is checked and compiled first, so that the macro can run; a site there would need the macro before it exists.

Move the macro into a module of its own and import it, or move the site.

Wrong

import std.syntax { Expr };

macro echo(e: Expr): Expr {
    return e;
}

fn main(): void {
    assert(echo!(3) == 3);
}

Right

//- src/main.lyr
import app.macros { echo };

fn main(): void {
    assert(echo!(3) == 3);
}
//- src/macros.lyr
import std.syntax { Expr };

pub macro echo(e: Expr): Expr {
    return e;
}