Alternations

What if we want to match multiple strings? Say, we want to match the texts one, two, three, four, and five:

'one' | 'two' | 'three' | 'four' | 'five'

It’s that easy, just separate all alternatives with a vertical bar. This is called an alternation. The | can be read as “or”, since the above matches 'one' or 'two' or 'three' or 'four' or 'five'.

Grouping #

If we want to concatenate an alternation, we need to wrap it in parentheses:

('blue' | 'yellow' | 'green') 'ish'

This matches blueish, yellowish, and greenish. Every expression can be surrounded by parentheses, this is called a group. Here the parentheses are needed to clarify that the ish is concatenated with the entire alternation, not just the green part.

Formatting #

When your expression gets so long that it doesn’t fit in a single line, it looks better to put every alternative in a separate line:

'one'
| 'two'
| 'three'
| 'four'
| 'five'

But this looks odd, because the first line is not aligned with the others. So Pomsky allows you to add a leading vertical bar:

| 'one'
| 'two'
| 'three'
| 'four'
| 'five'