diff options
Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 22 |
1 files changed, 14 insertions, 8 deletions
@@ -7247,18 +7247,17 @@ by <list> and <init-value> to a single value by the repeated application of <binary-function>. An effective list of operands is formed by combining <list> and -<init-value>. If <key-function> is specified and not nil, then -the items of <list> are mapped to a new values through <key-function>. -If an <init-value> is supplied and not nil, then in the -case of reduce-left, the effective list of operands is formed by prepending -<init-value> to <lits>. In the case of reduce-right, the effective +<init-value>. If <key-function> is specified, then the items of <list> are +mapped to a new values through <key-function>. If <init-value> is supplied, +then in the case of reduce-left, the effective list of operands is formed by +prepending <init-value> to <lits>. In the case of reduce-right, the effective operand list is produced by appending <init-value> to <list>. The production of the effective list can be expressed like this, -though this is not to be understood as the actual impelmentation: +though this is not to be understood as the actual implementation: ;; reduce-left - (let ((eff-list (append (if init-value (list init-value)) + (let ((eff-list (append (if init-value-present (list init-value)) [mapcar (or key-function identity) list]))) In the reduce-right case, the arguments to append are reversed. @@ -7273,6 +7272,13 @@ If the effective list contains one item, then that item is returned. Otherwise, the effective list contains two or more items, and is decimated as follows. +Note that an <init-value> specified as nil is not the same as a missing +<init-value>; this means that the initial value is the object nil. Omitting +<init-value> is the same as specifying a value of : (the colon symbol). +It is possible to specify <key-function> while omitting an <init-value> +argument. This is achieved by explicitly specifying : as the <init-value> +argument. + Under reduce-left, the leftmost pair of operands is removed from the list and passed as arguments to <binary-function>, in the same order that they appear in the list, and the resulting value initializes an @@ -7282,7 +7288,7 @@ from the list. After each call, the accumulator is updated with the return value of <binary-function>. The final value of the accumulator is returned. Under reduce-right, the list is processed right to left. The rightmost -pair of elements in the effetive list is removed, and passed as arguments to +pair of elements in the effective list is removed, and passed as arguments to <binary-function>, in the same order that they appear in the list. The resulting value initializes an accumulator. Then, for each remaining item in the list, <binary-function> is invoked on two arguments: the |