Compile-time expressions in Mojo

An ordinary function runs at compile time when its result feeds a comptime binding.

def factorial(n: Int) -> Int:
    var result = 1
    for i in range(2, n + 1):
        result *= i
    return result


comptime SEATS = 5
comptime ORDERINGS = factorial(SEATS)
comptime LABEL = "orderings: " + String(ORDERINGS)


def main():
    print(SEATS, ORDERINGS)
    print(LABEL)

How it works

factorial is a plain def with a plain runtime body.
comptime ORDERINGS = factorial(SEATS) runs it during compilation.
LABEL shows that string building folds ahead of time too.

Keywords and builtins used here

Int
String
def
factorial
for
main
print
range
return
var

The run, in numbers

Lines: 15
Characters to type: 257
Tokens: 67
Three-star pace: 70 tpm

At the three-star pace of 70 tokens a minute, this run takes about 57 seconds.

Type this snippet

Step 4 of 5 in Compile-time Mojo, step 4 of 22 in Parameters & SIMD.

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