Here is another example. Consider two functions f and g which, given the same inputs, always return the same outputs as each other such as:
f x = x + 2 g x = x + 1 + 1
Now since f and g compute the same results for the same inputs, anywhere in a program that you can use f you could just replace f by g and the observable behaviour of the program would be completely unaffected. This is what referential transparency means.
Another example: In haskell the following is true: f x + g x == g x + f x Pure functions in Haskell do not have side effects, so for the same inputs they always give back the same output. This is referential transparency. In a language such as C, which does not have referential transparency, the functions f and g may change x by a side effect and therefore: f x + g x /= g x + f x In C (or a language with side effects). Cheers, Chris. Christopher Brown PhD Student, University of Kent. http://www.cs.kent.ac.uk/people/rpg/cmb21/ cmb21@kent.ac.uk