This program contains a function called typoDistance, which takes in two strings as arguments.  This function finds the typo distance between the two strings, which is the likelihood that the second string is a typo of the first, as measured by a floating point number.  The lower the number, the more likely it is that the second string is a typo of the first.

Thus, for instance, "rlephants" is a fairly likely typo of "elephants" on a QWERTY keyboard, since R is fairly close to E, but "ilephants" is a less likely typo, and therefore would have a higher score.  One thing to note is that typoDistance is not commutative, since insertions are considered more costly than deletions.

typoDistance takes in an optional third argument, layout.  This argument is a string that allows a user to change the keyboard layout.  Currently, only 'QWERTY' is supported.

This program also contains a function called typoGenerator, which essentially reverses this process.  Given a start phrase s and a maximum typo distance d, typoGenerator returns a generator which will iterate through every string whose typo distance is less than or equal to d from s.  Like typoDistance, typoGenerator can take in an optional layout argument.  typoGenerator's output is not de-duplicated, since a given string can be gotten through multiple different actions.  For example, starting from the string "testString," we can get to "t3stString" by either substituting e with 3 or by deleting e and inserting 3.

This code was written on December 25, 2011 and January 1, 2012.  I hereby release it into the public domain and release all rights over it.