Assert

assert_param

Asserts that the condition is true in the parameter / comptime domain, used to place constraints on functions

from Assert import assert_param

We can put compile time assertions in the ensure that the two numbers passed in are positive

fn add_positives[x: Int, y: Int]() -> UInt8:
    assert_param[x > 0]()
    assert_param[y > 0]()
    return x + y

Let's get the result that's calculated at compile time

let res = add_positives[2, 4]()
print(res)

6

Now we'll introduce the error so you can see how it looks, it will always be at the end of the error message:

add_positives[-2, 4]()

Expression [2]:6:24:               constraint failed: param assertion failed
    assert_param[x > 0]()
                       ^

expression failed to parse (no further compiler diagnostics)

You can also add a message to change the compiler error output:

fn add_positives[x: Int, y: Int]() -> UInt8:
    assert_param[x > 0, "x is not positve, use a positve number over 0"]()
    assert_param[y > 0, "y is not positve, use a positve number over 0"]()
    return x + y

let res = add_positives[-2, -4]()
print(res)

Expression [5]:6:73:               constraint failed: x is not positve, use a positve number over 0
    assert_param[x > 0, "x is not positve, use a positve number over 0"]()
                                                                        ^

expression failed to parse (no further compiler diagnostics)

debug_assert

Asserts that the condition is true in debug builds, and is removed from the compilation process in release builds

from Assert import debug_assert

fn test_debug_assert[x: Int](y: Int):
    debug_assert(x == 42, "x is not equal to 42")
    debug_assert(y == 42, "y is not equal to 42")


test_debug_assert[1](2)

debug_assert doesn't work in the playground because it's not a debug build.