How to handle division by zero error in ML

Question

I am new to ML.

I need to define a function that takes a conditional expression as an argument, the problem is that the expression is not valid, for example "10 div 0 = 0" . How can I handle this?

For example, a function is defined as follows: foo exp1 = if (exp1) then ... else... , and exp1 - "10 div 0 = 0" , how to handle this separation error.

Answer 1

It sounds like you want to ask about the exception handling mechanism in SML.

The div function in the SML core library raises the Div exception when calling 10 div 0 . It depends on whether you need a value or not to handle the exception. You can either return true / false, or the option type in this case:

 (* only catch exception, ignore value *) fun div_check (x, y) = ( ignore (x div y); false ) handle Div => true (* catch exception and return option value *) fun div_check2 (x, y) = ( SOME (x div y) ) handle Div => NONE 

UPDATE:

It is very strange that in this case the compiler does not throw a div exception. I suggest you define a custom div function and call / handle exceptions yourself:

 exception DivByZero; (* custom div function: raise DivByZero if y is zero *) infix my_div; fun x my_div y = if y=0 then raise DivByZero else x div y fun div_check (x, y) = ( ignore (x my_div y); false ) handle DivByZero => true fun div_check2 (x, y) = ( SOME (x my_div y) ) handle DivByZero => NONE