diff options
Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 140 |
1 files changed, 114 insertions, 26 deletions
@@ -17795,15 +17795,40 @@ string, then is returned. Otherwise the first character of the string or first element of the vector is returned. +.meta object +may be a structure. The +.code car +operation is possible if the object has a +.code car +method. If so, +.code car +invokes that method and returns whatever the method returns. +If the structure has no +.code car +method, but has a +.code lambda +method, then the +.code car +function calls that method with one argument, that being +the integer zero. Whatever the method returns, +.code car +returns. If neither method is defined, an error +exception is thrown. + A .code car -form denotes a valid place when +form denotes a valid place whenever .meta object -is accessible via -.codn car , -isn't the object -.codn nil , -and is modifiable. +is a valid argument for the +.code rplaca +function. Modifying the place denoted by the form is equivalent to invoking +.code rplaca +with +.meta object +as the left argument, and the replacement value as the right +argument. It takes place in the manner given under the description +.code rplaca +function, and obeys the same restrictions. A .code car @@ -17894,17 +17919,52 @@ and both result in .codn nil . +If +.meta object +is a structure, then +.code cdr +requires it to support either the +.code cdr +method or the +.code lambda +method. If both are present, +.code cdr +is used. When the +.code cdr +function uses the +.code cdr +method, it invokes it with no arguments. +Whatever value the method returns becomes the +return value of +.codn cdr . +When +.code cdr +invokes a structure's +.code lambda +method, it passes as the argument the range object +.codn "#R(1 t)" . +Whatever the +.code lambda +method returns becomes the return value of +.codn cdr . + The invocation syntax of a .code cdr or .code rest -form is a syntactic place. The place is semantically valid when +form is a syntactic place. +The place is semantically correct if .meta object -is accessible via -.codn cdr , -isn't the object -.codn nil , -and is modifiable. +is a valid argument for the +.code rplacd +function. Modifying the place denoted by the form is equivalent to invoking +.code rplacd +with +.meta object +as the left argument, and the replacement value as the right +argument. It takes place in the manner given under the description +.code rplacd +function, and obeys the same restrictions. A .code cdr @@ -17969,11 +18029,13 @@ fails and the loop terminates. .coNP Functions @ rplaca and @ rplacd .synb -.mets (rplaca < cons << new-car-value ) -.mets (rplacd < cons << new-cdr-value ) +.mets (rplaca < object << new-car-value ) +.mets (rplacd < object << new-cdr-value ) .syne .desc -The +If +.code object +is a cons cell or lazy cons cell, then .code rplaca and .code rplacd @@ -17981,8 +18043,9 @@ functions assign new values into the .code car and .code cdr -fields of the cell -.metn cons . +fields of the +.metn object . +In addition, these functions are meaningful for other kinds of objects also. Note that, except for the difference in return value, .code "(rplaca x y)" @@ -17993,15 +18056,6 @@ and likewise can be written as .codn "(set (cdr x) y)" . -It is an error if -.meta cons -is not a cons or lazy cons. In particular, -whereas -.code "(car nil)" -is correct, -.code "(rplaca nil ...)" -is erroneous. - The .code rplaca and @@ -18040,6 +18094,40 @@ specifies the contents of the entire string or vector, as if the operation were done on a non-empty vector or string, followed by the deletion of the first element. +The +.meta object +argument may be a structure. In the case of +.codn rplaca , +the structure must have a defined +.code rplaca +method or else, failing that, a +.code lambda-set +method. The first of these methods which is available, in the given order, is +used to perform the operation. Whatever the respective method returns, +If the +.code lambda-set +method is used, it is called with two arguments (in addition to +.codn object ): +the integer zero, and +.metn new-car-value . + +In the case of +.codn rplacd , +the structure must have a defined +.code rplacd +method or else, failing that, a +.code lambda-set +method. The first of these methods which is available, in the given order, is +used to perform the operation. Whatever the respective method returns, +If the +.code lambda-set +method is used, it is called with two arguments (in addition to +.codn object ): +the range value +.code "#R(1 t)" +and +.metn new-car-value . + .coNP Accessors @, second @, third @, fourth @, fifth @, sixth @, seventh @, eighth @ ninth and @ tenth .synb .mets (first << object ) |