Advanced Patterns

Here are some additional pattern forms that are useful:

• p1 | ... | pn: an "or" pattern; matching against it succeeds if a match succeeds against any of the individual patterns pi, which are tried in order from left to right. All the patterns must bind the same variables.
• (p : t): a pattern with an explicit type annotation.
• c: here, c means any constant, such as integer literals, string literals, and booleans.
• 'ch1'..'ch2': here, ch means a character literal. For example, 'A'..'Z' matches any uppercase letter.
• p when e: matches p but only if e evaluates to true.

You can read about all the pattern forms in the manual.