Expression Macros

Sometimes you want to use macros to create small code transformations that result in an expression (ie. not an if-else, for, while or definition). For this purpose, you can use the second type of macro that Ryna has: expression macros. Let"s see how they work.

Syntax

An expression macro can be created in Ryna using this syntax:

syntax expr macro_name from NDL_Pattern {
    [...]
}

You can see that the syntax is almost the same, but contains the expr keyword. The other thing that changes is how they are compiled internally:

syntax expr double_integer from "Dbl" Arg(1{d}, n) {
    $n + $n
}

// This macro ...
print(Dbl6);

// ... is compiled to this
print(6 + 6);

You might be worrying about operator precedence by looking at this, but the interpreter ensures that the expression inside the macro is kept as-is, so you could use it like this:

// This macro ...
print(2 * Dbl6);

// ... is compiled to this ...
print(2 * (6 + 6));

// ... not to this
print(2 * 6 + 6);