Course of Raku / Advanced / Subroutines / More on MAIN subroutines / Exercises

A typed MAIN

Problem

A type constraint on a MAIN parameter is also checked before the body runs. Write a program whose MAIN takes a single Int $n and prints $n doubled. If the argument is not a valid integer, the signature does not match and Raku prints the usage message instead — you get the validation for free.

Example

$ raku typed-main.raku 5
10

$ raku typed-main.raku abc
Usage:
  typed-main.raku <n>

Solution

✅ See the solution

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