Macro dsl_function 

macro_rules! dsl_function {
    (fn $name:ident ( $($param:ident),* $(,)? ) = $body:expr ;) => { ... };
}

Define a helper that returns the DSL source definition of a reusable raster-algebra function.

This does not register a Rust-callable function and does not evaluate anything: it expands to pub fn <name>() -> String returning a syntactically valid DSL function declaration such as "fn ndvi(nir, red) = (nir - red) / (nir + red);". Prepend that string to a DSL program and then call the function from a DSL expression to use it.

Examples

use oxigeo_algorithms::dsl_function;
use oxigeo_algorithms::dsl::RasterDsl;

dsl_function! {
    fn ndvi(nir, red) = (nir - red) / (nir + red);
}

// `ndvi()` yields the DSL source; splice it into a program and call it.
let program = format!("{}\nndvi(B1, B2);", ndvi());
let dsl = RasterDsl::new();
// dsl.execute(&program, &[nir_band, red_band]) -> resulting raster