zipis already there, and it's called
List.combine. I hadn't noticed this.
Also, Robert Pickering, author of the upcoming APress book Foundations of F#, responded on his blog with a short version of the ROT13 algorithm, using only functions already present in the current library:
It basically uses
List.mapiinstead of my combo of
List.mapimaps a function over a list, but this function gets as arguments the list element and its index. And mapping over a string is implemented by converting the string to a char array, using
Array.mapover it and then creating a new string based on the result.