Question

I am new to SML.
How do I use the AND operator inside IF statements?
Here is my code:

val y = 1;
val x = 2;
if (x = 1 AND y = 2) then print ("YES ") else print("NO ");

My error is:
stdIn:66.9-67.3 Error: unbound variable or constructor: AND
stdIn:66.3-67.9 Error: operator is not a function [literal]
operator: int
in expression:
1
stdIn:66.3-67.9 Error: operator and operand don’t agree [literal]
operator domain: bool * bool
operand: bool * int
in expression:
x = (1 ) y = 2

Thank you

Answer 1

There is no AND operator in SML (unless you define one yourself). There is an and keyword, but you can’t use it inside if statements (or generally as a part of any expression) because it’s not an operator. It’s used in combination with fun to define mutually recursive functions.

You’re probably looking for the andalso operator, which takes two boolean operands and returns true if and only if both operands are true.