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From the Lips's perspective it is a contradiction. Something is either a function or a constant. The logic is that this object could be called as a function an

From the Lips's perspective it is a contradiction. Something is either a function or a constant. The logic is that this object could be called as a function and at the same time always evaluated to itself? That means whenever you call it you always getting it back - this is behavior of a constant. But if you could call it with an argument, you will get back some value, different from whatever it is? As long as maps are immutable, it will behave as a function - return the same value for the same argument. OK, but, please, don't tell me that this isn't confusing.)

chc 14y ago
> That means whenever you call it you always getting it back - this is behavior of a constant. No! You're confusing functions-as-callable-things and functions-as-values. The phrase "a constant" does not generally imply anything about a thing's behavior when called. It just means something whose value will never change. A self-evaluating constant is a constant that circularly evaluates to itself — nothing else can have that value without referring to the constant. But neither of these things have to do with calling anything; they're just about taking values. A constant can certainly refer to a function that returns something other than that constant. For example, in Ruby: `Example = lambda { 1 }`. If you just evaluate "Example", you will get a Proc value, but if you call Example, you will get the Fixnum 1. In most languages that have them, you cannot call a self-evaluating constant. It won't return itself — it's just not a callable thing. In Clojure, keywords are self-evaluating constants that have the behavior of looking themselves up as a key in the argument when called. They serve the purpose of self-evaluating constants exactly the same as in other languages, but they also have the handy property of doing map lookups.
- baar 14y ago
  Good explanation! Evaluation is what happens when you give something as a parameter. Calling is what happens when you do "(f ...)". Just a little concrete example: Welcome to Racket v5.3.1. > 'foo 'foo > ('foo) application: not a procedure; expected a procedure that can be applied to arguments given: 'foo arguments...: [none] context...: /usr/lib/racket/collects/racket/private/misc.rkt:87:7
- chc 14y ago
  @baar: FYI, you appear to be hellbanned (your comments are being automatically killed as soon as you post them). New accounts are particularly susceptible to this, as it seems like the auto-ban algorithm kicks in when you have low karma and get too many downvotes in a short time, or something like that. You should be OK if you make a new account and avoid making very harsh comments so you don't draw downvotes.
  - baar 14y ago
    (Just in case you can see this:) Thanks for letting me know. I'd figured as much (from browsing anonymously) -- I guess the powers that be don't care enough to get new commenters. Oh well. I won't bother to create a new account; I really shouldn't wasting time posting here anyway.

chc 14y ago

> That means whenever you call it you always getting it back - this is behavior of a constant. No! You're confusing functions-as-callable-things and functions-as-values. The phrase "a constant" does not generally imply anything about a thing's behavior when called. It just means something whose value will never change. A self-evaluating constant is a constant that circularly evaluates to itself — nothing else can have that value without referring to the constant. But neither of these things have to do with calling anything; they're just about taking values. A constant can certainly refer to a function that returns something other than that constant. For example, in Ruby: `Example = lambda { 1 }`. If you just evaluate "Example", you will get a Proc value, but if you call Example, you will get the Fixnum 1. In most languages that have them, you cannot call a self-evaluating constant. It won't return itself — it's just not a callable thing. In Clojure, keywords are self-evaluating constants that have the behavior of looking themselves up as a key in the argument when called. They serve the purpose of self-evaluating constants exactly the same as in other languages, but they also have the handy property of doing map lookups.

baar 14y ago
Good explanation! Evaluation is what happens when you give something as a parameter. Calling is what happens when you do "(f ...)". Just a little concrete example: Welcome to Racket v5.3.1. > 'foo 'foo > ('foo) application: not a procedure; expected a procedure that can be applied to arguments given: 'foo arguments...: [none] context...: /usr/lib/racket/collects/racket/private/misc.rkt:87:7
chc 14y ago
@baar: FYI, you appear to be hellbanned (your comments are being automatically killed as soon as you post them). New accounts are particularly susceptible to this, as it seems like the auto-ban algorithm kicks in when you have low karma and get too many downvotes in a short time, or something like that. You should be OK if you make a new account and avoid making very harsh comments so you don't draw downvotes.
- baar 14y ago
  (Just in case you can see this:) Thanks for letting me know. I'd figured as much (from browsing anonymously) -- I guess the powers that be don't care enough to get new commenters. Oh well. I won't bother to create a new account; I really shouldn't wasting time posting here anyway.