cases: Dispatches from an expression to a matching pattern
In pmatch: Pattern Matching

Description Usage Arguments Value See Also Examples

Given an expression of a type defined by the := operator, cases matches it against patterns until it find one that has the same structure as expr. When it does, it evaluates the expression the pattern is associated with. During matching, any symbol that is not quasi-quoted will be considered a variable, and matching values will be bound to such variables and be available when an expression is evaluated.

1	cases(expr, ...)

`expr`	The value the patterns will be matched against.
`...`	A list of `pattern -> expression` statements.

The value of the expression associated with the first matching pattern.

:=

linked_list := NIL | CONS(car, cdr : linked_list)
lst <- CONS(1, CONS(2, CONS(3, NIL)))
len <- function(lst, acc = 0) {
    cases(lst,
          NIL -> acc,
          CONS(car,cdr) -> len(cdr, acc + 1))
}
len(lst)

list_sum <- function(lst, acc = 0) {
    cases(lst,
          NIL -> acc,
          CONS(car,cdr) -> list_sum(cdr, acc + car))
}
list_sum(lst)