Course of Raku / Regexes and grammars / Grammars / Action classes / Exercises / Humanise a date

Solution: Humanise a date

Here is a possible solution to the task.

Code

grammar Date {
    token TOP   { <year> '-' <month> '-' <day> }
    token year  { \d ** 4 }
    token month { \d ** 2 }
    token day   { \d ** 2 }
}

class Humanise {
    method year($/)  { make $/.Int }
    method month($/) { make <January February March April May June
                             July August September October November December>[$/ - 1] }
    method day($/)   { make $/.Int }
    method TOP($/)   { make "{$<day>.made} {$<month>.made} {$<year>.made}" }
}

say Date.parse('2026-07-05', actions => Humanise.new).made;

🦋 You can find the source code in the file humanise-a-date.raku.

Output

5 July 2026

Comments

1. Unlike a plain arithmetic action, the token methods make values of different kinds: year and day make integers, but month makes a string by using its numeric value as an index into a list of month names. $/ - 1 numifies the two-digit match (07 → 7) and shifts to a zero-based index, so month 07 makes July.

2. The TOP method never re-examines the raw text. It just reads the three values the sub-methods already made — $<day>.made, $<month>.made, $<year>.made — and interpolates them into the final string. Reading 5 back from day also drops the leading zero for free.

3. This is the everyday job of an action class: parse structured input once, then let each method turn its own piece into whatever the rest of the program needs.

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