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Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 49 |
1 files changed, 49 insertions, 0 deletions
@@ -10300,6 +10300,13 @@ are made to work with strings and vectors: (car #(1 2 3)) -> 1 .cble +Moreover, structure types which define the methods +.codn car , +.code cdr +and +.code nullify +can also be treated in the same way. + The .code ldiff function is also extended in a special way. When the right parameter @@ -19288,6 +19295,48 @@ is defined for a structure type, then it is used for pretty-printing instances of that type. The method takes one argument (in addition to the object), which specifies the output stream. +.NP* Sequence Operations on Structures + +Structures may be treated as sequences if they define methods named +by the symbols +.codn car , +.codn cdr , +and +.codn nullify . + +If a structure supports these methods, then these methods are used +by the functions +.codn car , +.codn cdr , +.codn nullify , +.code empty +and various other sequence manipulating functions derived from them, when those +functions are applied to that object. + +An object which implements these three methods can be considered to denote +an abstract sequence. The object's +.code car +method should return the first value in that abstract sequence, or else +.code nil +if that sequence is empty. + +The object's +.code cdr +method should return an object denoting the remainder of the sequence, +or else +.code nil +if the sequence is empty or contains only one value. This returned object can +be of any type: it may be of the same structure type as that object, a +different structure type, a list, or whatever else. If a non-sequence object +is returned. + +The +.code nullify +method should return +.code nil +if the object is considered to denote an empty sequence. Otherwise it +should return that object itself. + .coNP Macro @ defstruct .synb .mets (defstruct >> { name | >> ( name << arg *)} < super |