Referential Transparency

Refential transparency is the property of a term A that it may be replaced by any other term B if term B accepts precisely the same set of inputs as term A and given any input B will produce the precisely same output as A. Refential transparency can be thought of as a functional or behavioral equivalence.

For example [1 2 + +] is referentially transparent and can be replaced with [3 +].

Only functions or expressions with no side-effects (in other words are pure) are referentially transparent.

Refential transparency is an important property to identify for optimization.