digit: int -> string
that maps integers in the range
0..35 to their numeric representation as a string. For example,
digit 0 = "0" digit 9 = "9" digit 10 = "A" digit 35 = "Z"
Note that every character has a unique implementation dependent code; the ML function ord: string -> int returns the code of the first character of a string, and the ML function chr: int -> string returns the character corresponding to a code.
An ML programmer can assume that the codes for digits are contiguous, as are the codes for letters; for example,
chr(ord("A") + 1) = "B"
words 1004 = "one thousand and four"