FP in Popular Languages and Libraries

Where the ideas show up

JavaScript/TypeScript: first-class functions, array methods, spread, readonly types; libraries such as Ramda, lodash/fp, fp-ts, Effect and Immer. Python: comprehensions, generators, itertools (chain, islice, groupby, accumulate), functools (reduce, partial, lru_cache), frozen dataclasses and match. Java: lambdas and the Streams API since Java 8, Optional, records and sealed types in newer versions. Kotlin: collection operations, lazy Sequence, data and sealed classes. Rust: iterators with closures, Option/Result with the ? operator, immutable-by-default bindings. Haskell: pure and lazy by default, effects tracked in types. Elixir: immutable data, pattern matching and the |> pipe operator on the BEAM. Check each language's docs for the version you use.

From concepts to real projects

FP ideas appear across languages, frontend frameworks and data pipelines, with trade-offs worth knowing.

itertools and functools in Python

Standard library FP tools.

from functools import reduce, partial, lru_cache
from itertools import accumulate, groupby, islice, count
from operator import add

running_totals = list(accumulate([3, 1, 4, 1, 5]))     # [3, 4, 8, 9, 14]
total = reduce(add, [3, 1, 4, 1, 5], 0)                  # 14
first_squares = list(islice((n * n for n in count(1)), 5))  # [1, 4, 9, 16, 25]

words = sorted(["apple", "avocado", "banana", "blueberry", "cherry"])
by_letter = {k: list(g) for k, g in groupby(words, key=lambda w: w[0])}
# groupby only groups adjacent items, hence the sort first

to_int = partial(int, base=2)          # to_int("101") returns 5

@lru_cache(maxsize=None)
def fib(n: int) -> int:
    return n if n < 2 else fib(n - 1) + fib(n - 2)

Use the idioms of the language

Bring FP concepts, not another language's syntax. Idiomatic Python favours comprehensions over chains of map and lambda; idiomatic Rust uses iterators and ? rather than hand-written monad helpers.

त्वरित जाँच: Which feature does Elixir provide for building pipelines?

• The `never` type
• The `?` operator
• Java Streams
• The `|>` pipe operator