Talk:Closure (computer programming)/to do

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Introduction
- Rewrite lead paragraph (mostly done)
  - In such languages a reference to a function is a reference to a closure...
  - Closure = Function + Environment
  - What happens when creating a closure? (Closure captures the current lexical environment)
  - What happens when entering a closure? (Function is executed in the lexical environment captured by the closure)
  - Picture?
  - Mention all relevant terminology: open, closed, free, bound, captured, closed over
  - Mention closures are an implementation technique for supporting first-class functions
  - Theory: closures in operational semantics
- Add an introductory section
  - Targeted primarily at imperative programmers who have little experience with non-local variables
- Closures are an implementation technique
  - A form of activation record on the heap
  - Compare with a stack-allocated version of activation records for nested functions
History
- Early languages:
  - POP-2, POP-11; POP-11: a practical language for artificial intelligence
  - PAL; 1968, 1970; http://www.softwarepreservation.org/projects/lang/PAL
  - Scheme; 1975
Semantics
- Closure (computer programming)#Differences in semantics: Scheme (variables in scope) vs. Smalltalk (variables + return + self) vs, Java 7/8/... (variables + return + this + exceptions + ...)
- Capturing loop variables
- Capture by reference vs. capture by copy, extending the lifetime and garbage collection (compare C++)
Implementation
- Luca Cardelli, Compiling a Functional Language.
- Simon Peyton Jones, Implementation of Functional Programming Languages.
- Z. Shao and A. W. Appel. Space-efficient closure representations.
- Upvalues: Roberto Ierusalimschy et al., "The Implementation of Lua 5.0"
- Funarg problems: closures are intended to solve the more difficult upwards funarg problem, but sometimes also used to solve the downwards.
Applications: thunk (delayed computation), memoization, object system, hidden state/static variables
- Closure (computer programming)#Closures and state representation: This can be used in lazy pure languages as well, e.g. storing a memoization table in the closure which is lazyily evaluated when needed but not discarded.

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