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Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 38 |
1 files changed, 38 insertions, 0 deletions
@@ -40078,6 +40078,44 @@ iterates over the strings and .codn "CA" . +A ranges of any kind may be derived into a +.IR "skip range" : +a range which skips elements. A skip range is expressed by a range +whose +.code to +element is a range, whose +.code to +element is a positive integer. This can be notated by an expression +which uses two instances of the +.code .. +(dot dot) range notation, +.codn X..Y..Z , +where +.code X..Y +must be a valid iterable range on its own, and +.code Z +must evaluate to a positive integer. +For instance +.code 0..10..2 +denotes a skip range which traverses the values +.codn 0 , +.codn 2 , +.codn 4 , +.code 6 +and +.codn 8 . +This syntax is equivalent to +.codn "(rcons 0 (rcons 10 2))" . +The implementation may be understood in terms of cascaded iteration +objects. In the abstract semantics, when +.code 0..10..2 +is passed to +.codn iter-begin , +a range iterator is first constructed for the range +.codn 1..10 . +Then a skip iterator is constructed, which takes every other element +from the range iterator. That skip iterator is returned. + Search trees are iterable. Iteration entails an in-order visits of the elements of a tree. A tree iterator created by .code tree-begin |