Course of Raku / Regexes and grammars / Grammars / What is a grammar / Exercises / Year and month

Solution: Year and month

Here is a possible solution to the task.

Code

my regex year  { \d ** 4 }
my regex month { \d ** 2 }

if '2025-06' ~~ / <year> '-' <month> / {
    say $<year>;
    say $<month>;
}

🦋 You can find the source code in the file year-token.raku.

Output

｢2025｣
｢06｣

Comments

1. Two named regexes are declared, each describing one piece of the date: a four-digit year and a two-digit month.

2. The pattern combines them with a literal dash between, and each is captured under its own name. Building a larger pattern from small named parts like this is exactly the idea a grammar formalises.

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