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Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 50 |
1 files changed, 50 insertions, 0 deletions
@@ -5470,6 +5470,56 @@ yields (1 2 3 4 5). In TXR Lisp, this usage can be simulated using .SS Functions reduce-left and reduce-right +.TP +Syntax: + +(reduce-left <binary-function> <list> <init-value> <key-function>) +(reduce-right <binary-function> <list> <init-value> <key-function>) + +.TP +Description: + +The reduce-left and reduce-right functions reduce lists of operands +specified in <list> to a single value by the repeated application of a +<binary-functions>. + +Otherwise, <init-value> begins either a left-associative reduction +under reduce-left, or a right-associative reduction under reduce-right. + +First, both functions initialize an internal accumulator with <init-value>. + +Under reduce-left, the list is processed left to right. If elements +remain to be processed, the <binary-function> is repeatedly called with two +arguments: the accumulator and the next element from the list. After each call, +the return value of the function replaces the accumulator. When no more items +remain, the accumulator is returned. + +Under reduce-right, the list is processed right to left. If elements +remain to be processed, the <binary-function> is repeatedly called with two +arguments: the next element from the list and the accumulator. After each call, +the return value of the function replaces the accumulator. When no more items +remain, the accumulator is returned. + +The <key-function> specifies how each element from the <list> is converted +to an argument to <binary-function>. The value nil is equivalent to +(fun identity), which means that each list element is taken as the value itself. + + +.TP +Examples: + +;;; list is empty, so 1 is just returned: +(reduce-left (fun +) () 1 nil) -> 1 + +;;; computes (- (- (- 0 1) 2) 3) +(reduce-left (fun -) '(1 2 3) 0 nil) -> -6 + +;;; computes (- 1 (- 2 (- 3 0))) +(reduce-right (fun -) '(1 2 3) 0 nil) -> 2 + +;;; computes (* 1 2 3) +(reduce-left (fun *) '((1) (2) (3)) 1 (fun first)) -> 6 + .SS Function copy-list .SS Functions reverse, nreverse |