Initial commit.
Parse an expression made of ints and operators.
Add error cases to README
Initial working implementation, almost.

Does not report errors correctly.
Revised implementation which errors correctly.
Use type instead of either.
Use liftM to avoid unpacking getArgs.
Use a type to represent operators.

Remove evaluate accordingly.
Use fromMaybe to remove use of case.
Add Makefile.
Update README and add LICENSE.