Macros

A macro is a rule or pattern that maps a given input to a replacement output. In other words, the assembler replaces a macro invocation with some other text (the macro expansion.)

Types

Macros in ETK take one of two forms: instruction macros, and expression macros. Both types of macros are written as a name followed by arguments in parentheses.

Instruction Macros

An instruction macro looks like this:

#![allow(unused)]
fn main() {
extern crate etk_asm;
let src = r#"
%macro push_sum(a, b)
    push1 $a + $b
%end

%push_sum(4, 2)
"#;
let mut output = Vec::new();
let mut ingest = etk_asm::ingest::Ingest::new(&mut output);
ingest.ingest(file!(), src).unwrap();
assert_eq!(output, &[0x60, 0x06]);
}

Instruction macros always begin with %, and expand to one or more instructions. In this case, %push_sum(4, 2) would expand to:

push1 0x06

Expression Macros

Expression macros do not begin with %, and cannot replace instructions. Instead, expression macros can be used in expressions. For example:

#![allow(unused)]
fn main() {
extern crate etk_asm;
let src = r#"
%def add_one(num)
    $num+1
%end

push1 add_one(41)
"#;
let mut output = Vec::new();
let mut ingest = etk_asm::ingest::Ingest::new(&mut output);
ingest.ingest(file!(), src).unwrap();
assert_eq!(output, &[0x60, 0x2a]);
}

Here, add_one(...) is an expression macro that returns the num+1. The fully expanded source would look like:

push1 42