Matching

Motivation

Want general purpose pattern matching, binding, unification. Possibly split into multiple services a la carte. My initial use case (generalizing how to limit reflection results) needs only matching, no binding or unification.

Issues

Based on a combination of my needs, the matching implementation I have proposed for clojure.data / reflection, and Drew Colthorp's matchure:

• desirable to support Clojure's equality partitioning
  • will never want assoc lists
  • limits cross-partition uses of existing destructuring
• minimize need for special forms
  • especially those such as matchure's "and" and "or" that usurp Clojure names
• so far, prefer argument order as in matchure
  • match is the "object", comes first
  • con: hurts ability to thread candidates via ->
• a la carte?
  • matching without binding is super simple
  • matchure does binding but no unification
• meaning of symbols
  • in matchure they are equality-matched (with some exceptions)
  • think I prefer evaluating them (quote them to prevent)
  • latter makes it easy to build new match patterns at runtime
• what is the syntax for guard-and-bind?
  • matchure uses (and (pred form) ?varname)
  • would like to find something that is used nowhere else
• currently no way to say "exactly this map/set", as extra keys are ignored
• currently no way to say "this value must not be present"
• considered an rejected parameterizing match with an atom-matching function
  • would allow different interpretations of e.g. string matching (case-insensitive, partial, etc.)
  • regexes cover all the string scenarios, and design already supports arbitrary functions