Cristian Baboi wrote:
http://en.wikipedia.org/wiki/First-class_object
The term was coined by Christopher Strachey in the context of “functions as first-class citizens” in the mid-1960's.[1]
Depending on the language, this can imply: 1. being expressible as an anonymous literal value 2. being storable in variables 3. being storable in data structures 4. having an intrinsic identity (independent of any given name) 5. being comparable for equality with other entities 6. being passable as a parameter to a procedure/function 7. being returnable as the result of a procedure/function 8. being constructable at runtime 9. being printable 10. being readable 11. being transmissible among distributed processes 12. being storable outside running processes
I'll guess that 5,9,12 does not apply to Haskell functions.
Exactly, together with 10 and 11 (when the distributed processes are on different machines). But there is good reason that those things can't be done in Haskell. With extensional equality (two functions are considered equal if they yield the same result on every possible argument) number 5 is undecidable. Similarly, there cannot be functions print :: (Int -> Int) -> String compile :: String -> (Int -> Int) with compile . print = id A print function based on an intensional representation (assembly, byte code, etc.) would have to distinguish extensionally equal functions print f ≠ print g although f = g which is not allowed. More importantly, I don't quite understand your question. If you definitively need 9-12 for a practical problem at hand, then you may want to take a look at the functional language Clean http://clean.cs.ru.nl/ which is similar to Haskell but offers 9-12 in some form. In all other cases, an email thread is not a good (often not even successful) way to get a coherent "world view" on Haskell (or on something else) since this necessarily involves nitpicking philosophical questions. In my experience, interrogating one person in real-time in audio and "interrogating" books are the best ways to do that. Concerning books, maybe The Haskell Road to Logic, Maths and Programming http://www.cwi.nl/~jve/HR is for you. More books on http://haskell.org/haskellwiki/Books You don't have to buy them, borrow them from a library. Regards, apfelmus