comp.js

comp.js

const reduce = Array.reduce;

// Call function `f` with value `x`.
const callWith = (x, f) => f(x);

// Pipe value `x` through many single-argument functions in succession.
// This is kind of like a Unix pipe. The value of the previous function is
// passed to the next function, etc. Note that functions are called
// from left-to-right, with left being first.
export const pipe = (x, ...f) => reduce(f, callWith, x);

// Combine a list of one-argument functions into a single one-argument function
// that will pipe `x` through each function.
// This is like the classic `compose` function, but goes from left-to-right
// instead of right-to-left.
// Returns a function.
export const chain = (...f) => (x) => pipe(x, ...f);

// Compose 2 functions.
const comp2 = (z, y) => (x) => z(y(x));

// Classic RTL function composition.
export const comp = (f, ...fn) => reduce(fn, comp2, f);

Forget method chaining with this one weird tip!