Why is code writen in functional programming language shorter than code writen in other programming paradigm languages?

Question

Many people say that code writen in functional programming language is shorter than code writen in other programming paradigm languages.But why?

Answer 1

One big reason is the greater use of higher-order functions. A simple example is map. The following are equivalent:

# Procedural psuedocode
result = []
for value in other_list:
    add somefunc(value) to result

# Functional pseudocode
let result = map(somefunc, other_list)

The higher-order function map abstracts away the code that iterates over the first list and sequentially adds the function return value to the new list. Other higher-order functions can be used to implement other techniques that are commonly spelled out (whether by necessity or not) in more detail in other paradigms.

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Another less commonly seen higher-order function is composition. In many languages, you write code like

def new_function(x):
    return func2(func1(x))

value = new_function(5)

or

lambda x: func2(func1(x))

In a functional style, you would write (or have) a compose function to handle the details, instead of having to write each composed function individually.

def compose(f, g):
    def _(x):
        return f(g(x))

value = compose(func2, func1)(x)

Some languages, like Haskell, even provide a composition operator:

value = (func2 . func1)(x)