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A typed lambda calculus is a typed formalism that uses the lambda-symbol ... (hence weak), but function applications that would duplicate terms instead name the ...
The purpose of β-reduction is to calculate a value. A value in lambda calculus is a function. So β-reduction continues until the expression looks like a function abstraction. A lambda expression that cannot be reduced further, by either β-redex, or η-redex is in normal form. Note that alpha-conversion may convert functions.
When combined with the idea of weak reduction, the resulting call-by-value reduction is indeed a faithful approximation. [19] Unfortunately, weak reduction is not confluent, [17] and the traditional reduction equations of the lambda calculus are useless, because they suggest relationships that violate the weak evaluation regime. [19]
In the lambda calculus, a beta redex is a term of the form: [3] [4] (.). A redex is in head position in a term , if has the following shape (note that application has higher priority than abstraction, and that the formula below is meant to be a lambda-abstraction, not an application):
Viewing the lambda calculus as an abstract rewriting system, the Church–Rosser theorem states that the reduction rules of the lambda calculus are confluent. As a consequence of the theorem, a term in the lambda calculus has at most one normal form, justifying reference to "the normal form" of a given normalizable term.
A lambda calculus system with the normalization property can be viewed as a programming language with the property that every program terminates. Although this is a very useful property, it has a drawback: a programming language with the normalization property cannot be Turing complete , otherwise one could solve the halting problem by seeing ...
In the 1930s Alonzo Church sought to use the logistic method: [a] his lambda calculus, as a formal language based on symbolic expressions, consisted of a denumerably infinite series of axioms and variables, [b] but also a finite set of primitive symbols, [c] denoting abstraction and scope, as well as four constants: negation, disjunction, universal quantification, and selection respectively ...
Java's lambda expressions are just syntactic sugar. Anything that can be written with a lambda expression can be rewritten as a call to construct an instance of an anonymous inner class implementing the interface, [ a ] and any use of an anonymous inner class can be rewritten using a named inner class, and any named inner class can be moved to ...