Programming Languages - Lambda

C++

#include <algorithm>
#include <cmath>

std::sort(x, x + n,
    [](float a, float b) {
        return (std::abs(a) < std::abs(b));
    }
);

In C++ you have to specify the values that are captured by the lambda. In other languages (e.g. Java and Rust) the compiler handles capturing without specifying the values.

• []: capture clause
• (): parameter list

Java

Collections.sort(vals, (a, b) ->
    Integer.compare(Math.pow(a, p), Math.pow(b, p)));

JavaScript

(a) => a * 2;

Python

Syntax: lambda arguments: expression.

E.g. lambda a: a + 1

• no multiple statements in a lambda.
• lambda cannot contain assignment.

>>> sorted([3, -2, -4, 5, 1], key=lambda x: abs(x))
[1, -2, 3, -4, 5]