This example shows how to write a lazy transformer.

This lazy tranformer implements a ROT13 converter. ROT13 (ROTate 13) is a classic substitution cipher which replaces each letter in the source file with the corresponding letter 13 places later in the alphabet. The source file should have a “.txt” extension and the converted file is created with a “.shhhh” extension.

Generally, only transformers that take a long time to run should be made lazy. This transformer is not particularly slow, but imagine that it might be used to convert the entire library of congress–laziness would then be a virtue.

For more information, see Writing a Lazy Transformer at: https://www.dartlang.org/tools/pub/transformers/lazy-transformer.html