http://www.cs.nyu.edu/paige/courses/sml/parser.sml
http://www.cs.nyu.edu/paige/courses/sml/interp1.sml
http://www.standardml.org/Basis/string.html
http://www.standardml.org/Basis/char.html
http://www.csci.csusb.edu/dick/samples/ml.functions.html