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> Javascript often has closures which are not lambdas - that's the usual form of a callback function. Can you clarify this further? To me a callback function

> Javascript often has closures which are not lambdas - that's the usual form of a callback function. Can you clarify this further? To me a callback function is a lambda. It may or may not be a closure.

saghm 9y ago
It seems like GP might have gotten it backwards; the usual form of a callback is a lambda that's not a closure. However, a callback function might not be either, e.g.: function foo(x) { return x + 1; } function bar(f, y) { return f(y); } // `foo` is a callback but neither a lambda nor a closure bar(foo, 2); edit: adding the missing the "b" in lambda
- the_common_man 9y ago
  Yeah, your explanation is consistent with my understanding.
- sillysaurus3 9y ago
  foo and bar are both lambdas and closures. A named lambda is still a lambda. foo = function (x) { return x + 1; } is identical to function foo (x) { return x + 1; } They are also closures. Since they don't refer to any outer variables, they are closures containing zero context variables. If foo were to refer to some other variable, the closure would contain one context variable. The only reason to distinguish between lambdas and closures is because some languages do not support closures (e.g. early versions of Emacs Lisp). Attempting to refer to other variables would always refer to a global variable with that name.
  - saghm 9y ago
    > foo and bar are both lambdas and closures. A named lambda is still a lambda. > foo = function (x) { return x + 1; } > is identical to > function foo (x) { return x + 1; } I'll concede that for JavaScript (and a few other languages); some languages don't treat all functions as just a lambda with a binding, though. > They are also closures. Since they don't refer to any outer variables, they are closures containing zero context variables. If foo were to refer to some other variable, the closure would contain one context variable. I'm not very keen on the definition of "closure" including functions that close over zero variables, because then "closure" becomes indistinguishable from "function", and the word is no longer useful. I might be wrong about the technical definition, but I feel like having a word for closures isn't very useful if it doesn't mean "closing over one or more variables".
    - sillysaurus3 9y ago
      Elisp disagrees: > (lambda () (print "hi")) (closure (t) nil (print "hi")) > (let ((a 1) (b 2)) (lambda () (print "hi"))) (closure ((b . 2) (a . 1) t) nil (print "hi")) > (let ((a 1)) (defun foo (x) (+ x 1))) foo > (symbol-function 'foo) (closure ((a . 1) t) (x) (+ x 1)) > (defun bar (x) (+ x 1)) bar > (symbol-function 'bar) (closure (t) (x) (+ x 1)) So yes, every function is a closure.
      - kukx 9y ago
        It depends on your definition of the closure. Example: "A closure is the combination of a function and the lexical environment within which that function was declared." [0] [0] https://developer.mozilla.org/en/docs/Web/JavaScript/Closures https://developer.mozilla.org/en/docs/Web/JavaScript/Closure...
        joshuamorton 9y ago
        A lexical environment being syonymous with "a set of 0 or more variables accessible from within the function, but not passed as arguments." The key piece of that being 0 or more. The null set is still a set.
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        kukx 9y ago
        I do not think it is useful to interpret it as 0 or more. To me it only make sense to assume 1 or more. Otherwise you could say that the programming language that do not support closing variables, has nonetheless closures, as according to that notion every function is a closure that closes nothing.
        9y ago
  - kukx 9y ago
    >A named lambda is still a lambda. Most commonly a lambda is regarded as an anonymous function. [0] If you name it, it is no longer anonymous. [0] - https://softwareengineering.stackexchange.com/questions/130722/what-is-the-difference-between-a-function-and-a-lambda/130785 https://softwareengineering.stackexchange.com/questions/1307...
  - barrkel 9y ago
    A named lambda isn't.

saghm 9y ago

It seems like GP might have gotten it backwards; the usual form of a callback is a lambda that's not a closure. However, a callback function might not be either, e.g.: function foo(x) { return x + 1; } function bar(f, y) { return f(y); } // `foo` is a callback but neither a lambda nor a closure bar(foo, 2); edit: adding the missing the "b" in lambda

the_common_man 9y ago
Yeah, your explanation is consistent with my understanding.
sillysaurus3 9y ago
foo and bar are both lambdas and closures. A named lambda is still a lambda. foo = function (x) { return x + 1; } is identical to function foo (x) { return x + 1; } They are also closures. Since they don't refer to any outer variables, they are closures containing zero context variables. If foo were to refer to some other variable, the closure would contain one context variable. The only reason to distinguish between lambdas and closures is because some languages do not support closures (e.g. early versions of Emacs Lisp). Attempting to refer to other variables would always refer to a global variable with that name.
- saghm 9y ago
  > foo and bar are both lambdas and closures. A named lambda is still a lambda. > foo = function (x) { return x + 1; } > is identical to > function foo (x) { return x + 1; } I'll concede that for JavaScript (and a few other languages); some languages don't treat all functions as just a lambda with a binding, though. > They are also closures. Since they don't refer to any outer variables, they are closures containing zero context variables. If foo were to refer to some other variable, the closure would contain one context variable. I'm not very keen on the definition of "closure" including functions that close over zero variables, because then "closure" becomes indistinguishable from "function", and the word is no longer useful. I might be wrong about the technical definition, but I feel like having a word for closures isn't very useful if it doesn't mean "closing over one or more variables".
  - sillysaurus3 9y ago
    Elisp disagrees: > (lambda () (print "hi")) (closure (t) nil (print "hi")) > (let ((a 1) (b 2)) (lambda () (print "hi"))) (closure ((b . 2) (a . 1) t) nil (print "hi")) > (let ((a 1)) (defun foo (x) (+ x 1))) foo > (symbol-function 'foo) (closure ((a . 1) t) (x) (+ x 1)) > (defun bar (x) (+ x 1)) bar > (symbol-function 'bar) (closure (t) (x) (+ x 1)) So yes, every function is a closure.
    - kukx 9y ago
      It depends on your definition of the closure. Example: "A closure is the combination of a function and the lexical environment within which that function was declared." [0] [0] https://developer.mozilla.org/en/docs/Web/JavaScript/Closures https://developer.mozilla.org/en/docs/Web/JavaScript/Closure...
      - joshuamorton 9y ago
        A lexical environment being syonymous with "a set of 0 or more variables accessible from within the function, but not passed as arguments." The key piece of that being 0 or more. The null set is still a set.
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        kukx 9y ago
        I do not think it is useful to interpret it as 0 or more. To me it only make sense to assume 1 or more. Otherwise you could say that the programming language that do not support closing variables, has nonetheless closures, as according to that notion every function is a closure that closes nothing.
        9y ago
- kukx 9y ago
  >A named lambda is still a lambda. Most commonly a lambda is regarded as an anonymous function. [0] If you name it, it is no longer anonymous. [0] - https://softwareengineering.stackexchange.com/questions/130722/what-is-the-difference-between-a-function-and-a-lambda/130785 https://softwareengineering.stackexchange.com/questions/1307...
- barrkel 9y ago
  A named lambda isn't.