Level 0 Patterns

Level0 pattern matchers provide a very limited set of patterns. These are used for implementing level 1 / 2 patterns. As this is merely a part of the compiler, the implementation of level 0 matcher is aimed at cleanness and not speed, or extensibility.

Available Patterns are restricted to: list, list*, cons, constant, variable, wildcard (_).

Any symbols are considered as variables, except for constant symbols (namely, t, nil and keywords) and those named as _ (checked by the symbol’s name, they don’t have to be exported). These are identical to the corresponding patterns in Optima.

Example:

(match0 tree
  ((list* x (list :hi! y _) _ z)
   (vector x y z)))

This example code checks if tree is a cons tree of length more than 3, and if the second element is a list of length 3, and if its first element is a constant `:hi!’. If they hold true, bind x, y and z and evaluate (vector x y z).

match0

returns the body of the first matching pattern. Returns NIL when all patterns fail.

ematch0

Same, but signals an error when all patterns fail. This is preferred over match0 since the compiler should be correct.

lambda-match0 and lambda-ematch0

expands to lambda which takes one argument and pass it to match0 and ematch0, respectively.