Macros

Warning

Feature is still experimental

Macros, while aren't exactly directives, they are kinda like decorators in TypeScript, but with more control.
You stick them on top of functions (only) and they get a chance to rewrite or extend how that thing behaves before the program even runs.

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Declaring Macros

To make a macro, mark a function with @{rew::types::macro}.
That tells the compiler: “this function doesn’t run at runtime, it rewrites code at compile time.”

It always receives (name, fn, ...args) where:

• name → the function’s name being wrapped
• fn → the original function definition
• ...args → whatever extra stuff you wrote after the macro

Example:

@{rew::types::macro}
function Log(name, fn)
  newFn = function(...args)
    print "[LOG]", name, "called with:", args
    result = fn.call(@, ...args)
    print "[LOG]", name, "returned:", result
    result
  newFn

Now Log can wrap any function to print its calls and return values.

NOTICE

Remember to import macro form #std.types, otherwise you will get an error.

Using Macros

Let’s say we have a math library:

@{Log}
function add(a, b)
  a + b

@{Log}
function mul(a, b)
  a * b

Calling them:

print add(2, 3)
# [LOG] add called with: [2, 3]
# [LOG] add returned: 5
# 5

The macro rewrote both functions to log automatically. No extra boilerplate — just tag it with @{Log}.

If you want to pass extra data, you can put it after the macro name. The first identifier is always the macro; the rest are passed in as arguments.

@{Log, "math", "core"}
function mul(a, b)
  a * b

Here:

• Log is the macro.

• "math", "core" get passed in as labels.

Output might look like:

[LOG] mul called with: [2, 3]
[LOG] mul returned: 6
[EXTRA LABELS] ["math", "core"]

Why This Matters

• Only one macro function runs per declaration (the first one).
• Everything else you list after it becomes extra arguments for that macro.
• This means you don’t “stack” macros, you “parameterize” one macro with other values or helpers.

So if you wrote:

@{Validate, Min(1), Max(10)}
function setAge(age)
  ...

Then only Validate is the macro. Min(1) and Max(10) are just arguments passed into it. Validate decides how to use them.