diff options
| -rw-r--r-- | txr.1 | 14 |
1 files changed, 10 insertions, 4 deletions
@@ -5122,10 +5122,10 @@ In ancient Lisp in the 1960's, it was not possible to apply the operations car and cdr to the nil symbol (empty list), because it is not a cons cell. In the InterLisp dialect, this restriction was lifted: these operations were extended to accept nil (and return nil). The convention was adopted in -other Lisp dialects and in Common Lisp. Thus there exists an object which -is not a cons, yet which takes car and cdr. +other Lisp dialects such as MacLisp and eventually in Common Lisp. Thus there +exists an object which is not a cons, yet which takes car and cdr. -In TXR Lisp, this concept is extended further. For the sake of convenience, +In TXR Lisp, this relaxation is extended further. For the sake of convenience, the operations car and cdr, are extended to work with strings and vectors: (cdr "") -> nil @@ -5154,7 +5154,13 @@ Derived list processing operations such as remq or mapcar obey the following rule: the returned object follows the type of the leftmost input list object. For instance, if one or more sequences are processed by mapcar, and the leftmost one is a character string, the function is expected to return -characters, which are converted to a character string. +characters, which are converted to a character string. However, in the +event that the objects produced cannot be assembled into that type of +sequence, a list is returned instead. + +For example [mapcar list "ab" "12"] returns ((#\ea #\eb) (#\e1 #\e2)), +because a string cannot hold lists of characters. However +[mappend list "ab" "12"] returns "a1b2". The lazy versions of these functions such as mapcar* do not have this behavior; they produce lazy lists. |