cannot call function that may raise in a context that cannot raise: mojo

Question

mojo version: mojo 0.2.1 (64d14e85)

the code:

struct MyPair:
    var first: Int
    var second: Int

    # We use 'fn' instead of 'def' here - we'll explain that soon
    fn __init__(inout self, first: Int, second: Int):
        self.first = first
        self.second = second

    fn __lt__(self, rhs: MyPair) -> Bool:
        return self.first < rhs.first or
              (self.first == rhs.first and
               self.second < rhs.second)


def pair_test() -> Bool:
    let p = MyPair(1, 2)
    # Uncomment to see an error:
    # return p < 4 # gives a compile time error
    return True

pair_test() # err!

err: TODO: expressions are not yet supported at the file scope levelmojo

cannot call function that may raise in a context that cannot raise: mojo main.(22, 10): try surrounding the call in a 'try' block

(function) def pair_test() raises -> Bool

then how to call the function?

Answer 1

I assume you are running this from the commandline, for example mojo foo.mojo. The pair_test function uses def which uses the Python interop layer, therefore this may raise an exception. One possible way to fix this is to use a main function and mark it with raises, for example

fn main() raises:
    pair_test()