SML's if then else statement needs the else! Can't get away with if then.
fun is a keyword for declaring functions, so you can't use it for a variable.
Semicolons are optional in the code of the file--they're required in the REPL.
Gotta type val before a new expression!
In the if expression, the then and else have to have matching expressions.
Minus is a binary operation in SML. Can't write val a = - 5...
Negation/negative is the TILDE character!
So you'd write val a = ~5 or val a = 0 - 5
Cannot use / division on integers. That's for floats. Gotta use div! 5 div 4 = 1. div is integer division.