7.2.6 decision ¶

Syntax ¶

(decision condition traversal-A traversal-B)

or

(if condition traversal-A traversal-B)

Description ¶

Do either traversal A or traversal B, depending on whether a condition holds.

The condition can be any predicate — either a built-in predicate form, or an arbitrary traversal, including a lambda. See Predicates for details.

Examples ¶

"If we’re at the root of the tree, then go forward, otherwise go down."

(symex-eval
  (symex-traversal
    (if (at root)
        (move forward)
        (move down))))

"If we are somewhere before a previously stored position in the buffer, then go forward, otherwise don’t move."

(symex-eval
 (symex-traversal
   (if (lambda (_computation _result)
         (< (point) previously-stored-position))
       (move forward)
       symex--move-zero)))

We’ll ignore the arguments of the lambda here, for now, and will soon see what they’re for. symex--move-zero is just a convenient traversal for cases where you need to indicate a traversal but would like to not move at all. It is defined as (symex-make-move 0 0).