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Alfred V. Aho
[email protected]

Lecture 2: Design and Implementation
of Lambda Expressions in Java 8

CS E6998-1: Advanced Topics in
Programming Languages and Compilers
September 15, 2014

Outline
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What is the lambda calculus?
What is functional programming?
What are the benefits of functional programming?
Functional programming in Java 8
Java 8 lambda expressions
Implementation of Java 8 lambda expressions
Streams

The Lambda Calculus
• The lambda calculus was introduced in the 1930s by Alonzo Church as a mathematical system for defining computable
functions.
• The lambda calculus is equivalent in definitional power to that of Turing machines.
• The lambda calculus serves as the computational model
underlying functional programming languages such as Lisp,
Haskell, and Ocaml.
• Features from the lambda calculus such as lambda expressions have been incorporated into many widely used programming
languages like C++ and now very recently Java 8.

What is the Lambda Calculus?
• The central concept in the lambda calculus is an
expression generated by the following grammar
which can denote a function definition, function
application, variable, or parenthesized expression:
expr → λ var . expr | expr expr | var | (expr)
• We can think of a lambda-calculus expression as a
program which when evaluated by beta-reductions
returns a result consisting of another lambdacalculus expression.

Example of a Lambda Expression
• The lambda expression

λ x . (+ x 1) 2
represents the application of a function λ x . (+ x 1)
with a formal parameter x and a body + x 1 to the
argument 2. Notice that the function definition
λ x . (+ x 1) has no name; it is an anonymous
function.
• In Java 8, we would represent this function definition
by the Java 8 lambda expression x -> x + 1 .

More Examples of Java 8 Lambdas
• A Java 8 lambda is basically a method in Java without a
declaration usually written as (parameters) -> { body }. Examples, 1. (int x, int y) -> { return x + y; }
2. x -> x * x
3. ( ) -> x

• A...

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