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Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 25 |
1 files changed, 25 insertions, 0 deletions
@@ -39818,6 +39818,31 @@ and binds a to the leftmost and fails to match a list like .codn "(1 2)" . +Pattern variables exist in the same namespace as Lisp variables, +and are fully integrated in it. Patterns not only bind variables, +but have visibility to existing variables in scope, including +lexical variables and special/global variables. When a variable +is mentioned in a pattern, if it already has a binding as a Lisp variable, then +it denotes a reference to that variable in exactly the same way that a pattern +variable back-references itself in a pattern: the Lisp variable +is require to compare +.code equal +to the corresponding object being examined by the pattern. For instance, +the following function returns the third element of a list, if the +first two elements are repetitions of the +.code x +argument, otherwise +.codn nil : + +.verb + (defun x-x-y (list x) + (when-match (@x @x @y) list y)) + + (x-x-y '(1 1 2) 1) -> 2 + (x-x-y '(1 2 3) 1) -> nil ;; no @x @x match + (x-x-y '(1 1 2 r2) 1) -> nil ;; list too long +.brev + The pattern-matching notation is documented in the following sections; sections describing the pattern matching macros follow. |