OpenMusic Reference
posn-match
posn-match
(lists module) -- Constructs a new list from a list of elements and a list of ordinal references
Syntax
posn-match list positions
Inputs
| name | data type(s) | comments |
|---|---|---|
| list | a tree | the list of elements to use as material |
| positions | a list of non-negative integers | The ordinal references for constructing the new list |
Output
| output | data type(s) | comments |
|---|---|---|
| first | a tree | a list composed of elements from list at the specified positions |
Description
posn-match constructs a new list by treating the list positions as a list of ordinal references and replacing them with the correspondint elements in list . The nesting of positions is maintained even though the elements are replaced. If the elements which replace them are themselves lists, additional nesting will be produced.
To reference the ordinal positions, posn-match supports the same syntax understood by the expand-lst function.
Elements in positions which refer to non-existant positions in list will be replaced by nil.
Examples
Constructing a list using literal ordinal references
posn-match will take ((0 1) 4 (6)) and replace those numbers with the ordinals they reference in the first list, keeping the nesting as is :
? OM->((10 20) 50 (70))
Constructing a list using ordinal references with the expand-lst syntax
Here is an example of using the expand-lst syntax to construct a list. The same first input list is used, but instead of literal ordinal references, positions uses the special syntax explained in the expand-lst entry.
The 3*(0) means that the element at position 0 will be repeated three times. Following that, the 3_6 means that the elements between positions 3 and 6 will be enumerated. The whole thing generates:
? OM->(10 10 10 40 50 60 70)
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