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| -rw-r--r-- | txr.1 | 29 |
1 files changed, 20 insertions, 9 deletions
@@ -39821,23 +39821,34 @@ occurrences of the variable must correspond to objects which are to that value, or else there is no match. For instance, the pattern .code "(@a @a)" -matches a list like +matches the list like .code "(1 1)" -and binds a to the leftmost -.codn 1 , -and fails to match a list like -.codn "(1 2)" . +as follows. First +.code @a +binds to the leftmost +.code 1 +and then the second +.code 1 +matches the existing value of that +.codn a . +An input such as +.code "(1 2)" +fails to match because the second occurrence of +.code @a +retrieves an object that is not +.code equal +to that variable's existing value. Pattern variables exist in the same namespace as Lisp variables, -and are fully integrated in it. Patterns not only bind variables, +and are fully integrated into 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, and is not freshly bound in that pattern using the .code as -operator, if it already has a binding a variable outside the pattern, then -it denotes a reference to that variable. That occurrence of the variable -must match an object which compares equal +operator, if that symbol already has a variable binding outside the pattern, +then it denotes a reference to that variable. Each occurrence of the variable +in the pattern must match an object which compares .code equal to the variable's existing value. For instance, the following function returns the third element of a list, if the |