A Word Ladder (also known as a doublets, word-links, or Word golf) is a word game invented by Lewis Carroll. A word ladder puzzle begins with two words, and to solve the puzzle one must find a chain of other words to link the two, where at each step the words differ by altering a single letter. Wikipedia
fsi .\word-ladder.fsx blue yuck
OR
fsc .\word-ladder.fsx .\word-ladder.exe blue yuck