Question

For a homework assignment, we’ve been instructed to complete a task without introducing any “side-effects”. I’ve looked up “side-effects” on Wikipedia, and though I get that in theory it means “modifies a state or has an observable interaction with calling functions”, I’m having trouble figuring out specifics.

For example, would creating a value that holds a non-compile time result be introducing side effects?

Say I had (might not be syntactically perfect):

val myList = (someFunction x y);;
if List.exists ((=) 7) myList then true else false;;

Would this introduce side-effects? I guess maybe I’m confused on what “modifies a state” means in the definition of side-effects.

Answer 1

No; a side-effect refers to e.g. mutating a ref cell with the assignment operator :=, or other things where the value referred to by a name changes over time. In this case, myList is an immutable value that never changes during the program, thus it is effect-free.

See also

http://en.wikipedia.org/wiki/Referential_transparency_(computer_science)