# Point-Free Style and Its Limits — Functional Programming Concepts

Source: https://www.geekswithgeeks.com/en/functional-programming/cp-pointfree

> Defining functions without naming their arguments.

## Elegant until it is not

**Point-free** (or tacit) style defines a function by composing other functions without mentioning its arguments: `const shout = pipe(toUpper, exclaim)` instead of `s => exclaim(toUpper(s))`. It removes noise when the pieces have clear names. It hurts when readers must mentally track argument order through `flip`, nested composition or library combinators, and stack traces show anonymous wrappers. In JavaScript it also has a classic trap: passing a function with optional extra parameters to `map`, such as `["1","2","3"].map(parseInt)`, which passes the index as the radix.

## Readable and unreadable point-free code

And the parseInt trap.

```typescript
const toUpper = (s: string) => s.toUpperCase();
const exclaim = (s: string) => `${s}!`;

const pipe2 = <A, B, C>(f: (a: A) => B, g: (b: B) => C) => (a: A): C => g(f(a));

// Point-free: no named argument
const shout = pipe2(toUpper, exclaim);
// Pointed equivalent: (s: string) => exclaim(toUpper(s))
const names = ['ada', 'alan'].map(shout);   // passing shout point-free is fine

// Trap: map passes (value, index, array)
const broken = ['1', '2', '3'].map(parseInt);
// parseInt('2', 1) and parseInt('3', 2) are NaN, so broken is [1, NaN, NaN]

// Explicit lambda states intent
const numbers = ['1', '2', '3'].map(s => parseInt(s, 10)); // [1, 2, 3]
```

## Name the intermediate steps

If a point-free chain needs a comment to explain it, give the argument a name or split the chain into named helper functions.

**Quiz:** Why does `["1","2","3"].map(parseInt)` misbehave?

- [ ] parseInt is not a function
- [x] map also passes the index, which parseInt treats as the radix
- [ ] map skips the first element
- [ ] Strings cannot be mapped

*Answer:* map also passes the index, which parseInt treats as the radix. Point-free passing forwards every argument the caller supplies.