Lambda lifting
meta-process that defines functions independently of each other in a global scope
Lambda lifting is a meta-process that restructures a computer program so that functions are defined independently of each other in a global scope. An individual lift transforms a local function (subroutine) into a global function. It is a two step process, consisting of:
Eliminating free variables in the function by adding parameters.
Moving functions from a restricted scope to broader or global scope.
The term "lambda lifting" was first introduced by Thomas Johnsson around 1982 and was historically considered as a mechanism for implementing programming languages based on functional programming. It is used in conjunction with other techniques in some modern compilers.
Lambda lifting is not the same as closure conversion. It requires all call sites to be adjusted (adding extra arguments (parameters) to calls) and does not introduce a closure for the lifted lambda expression. In contrast, closure conversion does not require call sites to be adjusted but does introduce a closure for the lambda expression mapping free variables to values.
The technique may be used on individual functions, in code refactoring, to make a function usable outside the scope in which it was written.
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