On Sun, Apr 7, 2013 at 12:43 AM, Henning Thielemann wrote:

Can someone enlighten me about the origin of the term "referential transparency"? I can lookup the definition of "referential transparency" in the functional programming sense in the Haskell Wiki and I can lookup the meaning of "reference" and "transparency" in a dictionary, but I don't know why these words were chosen as name for this defined property.

Instead of a immaculately precise definition, may I suggest going about it from the practical benefits POV? RT matters so much in Haskell because of the engineering leverage it gives us. Bird's Pearls are a good source of Why Equational Reasoning Matters. -- Kim-Ee

On 04/06/2013 08:43 PM, Henning Thielemann wrote:

Can someone enlighten me about the origin of the term "referential transparency"? I can lookup the definition of "referential transparency" in the functional programming sense in the Haskell Wiki and I can lookup the meaning of "reference" and "transparency" in a dictionary, but I don't know why these words were chosen as name for this defined property.

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I will recommend you book "Modern Compiler Design" by Dick Grune and others. Besides discussing different topics, authors use Haskell as example for describing ideas behind compilers for functional language. Here is citation from book on RT, which not explain who coined this term, but describes it generally : "By definition, a function in Haskell defines a fixed relation between inputs and out- put: whenever a function f is applied to the argument value arg it will produce the same output no matter what the overall state of the computation is. Haskell, like any other pure functional language, is said to be “referentially transparent” or “side- effect free.” This property does not hold for imperative languages, where assign- ments to global variables and through pointers may cause two function calls f arg to yield different results, even when the argument value arg is the same in both calls. The good thing about referential transparency is that it simplifies program anal- ysis and transformation since a closed expression always denotes the same value independent of the context, and may be moved around freely. A closed expression is an expression that contains no references to external names other than global iden- tifiers." -- Best regards, Sergey Bushnyak