Editing Schwartzian transform (section)

==Example==

For example, to sort a list of files by their [[mac times|modification times]], a naive approach might be as follows:

 '''function''' naiveCompare(file a, file b) {
     '''return''' modificationTime(a) < modificationTime(b)
 }
 
 ''// Assume that sort(list, comparisonPredicate) sorts the given list using''
 ''// the comparisonPredicate to compare two elements.''
 sortedArray := sort(filesArray, naiveCompare)

Unless the modification times are {{not a typo|memoized}} for each file, this method requires re-computing them every time a file is compared in the sort. Using the Schwartzian transform, the modification time is calculated only once per file.

A Schwartzian transform involves the functional idiom described above, which does not use temporary arrays.

The same algorithm can be written procedurally to better illustrate how it works, but this requires using temporary arrays, and is not a Schwartzian transform. The following example pseudo-code implements the algorithm in this way:

 '''for each''' file '''in''' filesArray
     insert array(file, modificationTime(file)) at end of transformedArray
 
 '''function''' simpleCompare(array a, array b) {
     '''return''' a[2] < b[2]
 }
 
 transformedArray := sort(transformedArray, simpleCompare)
 
 '''for each''' file '''in''' transformedArray
     insert file[1] at end of sortedArray