Recovering from an error in Mojo

A raising helper wrapped by a caller that supplies a fallback.

def ratio(top: Int, bottom: Int) raises -> Float64:
    if bottom == 0:
        raise Error("cannot divide by zero")
    return Float64(top) / Float64(bottom)

def safe_ratio(top: Int, bottom: Int) -> Float64:
    try:
        return ratio(top, bottom)
    except e:
        print("falling back:", String(e))
        return 0.0

def main():
    print(safe_ratio(7, 2))
    print(safe_ratio(7, 0))

How it works

1. ratio refuses a zero denominator and raises instead.
2. safe_ratio calls it inside try and returns the result on success.
3. The except arm reports the problem and returns 0.0 in its place.

Keywords and builtins used here

• Error
• Float64
• Int
• String
• def
• except
• if
• main
• print
• raise
• ratio
• return
• safe_ratio
• try

The run, in numbers

Lines

15

Characters to type

340

Tokens

96

Three-star pace

80 tpm

At the three-star pace of 80 tokens a minute, this run takes about 72 seconds.

Type this snippet

Step 3 of 3 in Errors, step 25 of 26 in Language basics.

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