cem2ran/recursive_map_filter_reduce.js

## recursive_map_filter_reduce.js
let map = (fn,[head, ...tail]) => head === undefined
	? []
	: [fn(head), ...map(fn,tail)]

console.log("map(x=>x+1,[1,2,3,4]) :",map(x=>x+1,[1,2,3,4]))

let filter = (predicate, [head, ...tail]) => head === undefined
	? []
	: predicate(head)
	? [head, ...filter(predicate, tail)]
	: filter(predicate, tail)

console.log("filter(x=>x>2,[1,2,3,4,5]) :", filter(x=>x>2,[1,2,3,4,5]))

let reduce = (fn, acc, [head, ...tail]) => head === undefined
	? acc
	: reduce(fn, fn(acc, head), tail);

console.log("reduce((x,y)=>x+y,0,[1,2,3,4]) :",reduce((x,y)=>x+y,0,[1,2,3,4]))

let map_derived = (f, list) => reduce((acc, next) => [...acc, f(next)], [], list);

console.log("map_derived(x=>x+1,[1,2,3,4]) :",map_derived(x=>x+1,[1,2,3,4]))

let filter_derived = (predicate, list) => reduce((acc, next) => predicate(next) ? [...acc, next] : acc, [], list);

console.log("filter_derived(x=>x>2,[1,2,3,4,5]) :", filter(x=>x>2,[1,2,3,4,5]))
	let map = (fn,[head, ...tail]) => head === undefined
	? []
	: [fn(head), ...map(fn,tail)]

	console.log("map(x=>x+1,[1,2,3,4]) :",map(x=>x+1,[1,2,3,4]))

	let filter = (predicate, [head, ...tail]) => head === undefined
	? []
	: predicate(head)
	? [head, ...filter(predicate, tail)]
	: filter(predicate, tail)

	console.log("filter(x=>x>2,[1,2,3,4,5]) :", filter(x=>x>2,[1,2,3,4,5]))

	let reduce = (fn, acc, [head, ...tail]) => head === undefined
	? acc
	: reduce(fn, fn(acc, head), tail);

	console.log("reduce((x,y)=>x+y,0,[1,2,3,4]) :",reduce((x,y)=>x+y,0,[1,2,3,4]))

	let map_derived = (f, list) => reduce((acc, next) => [...acc, f(next)], [], list);

	console.log("map_derived(x=>x+1,[1,2,3,4]) :",map_derived(x=>x+1,[1,2,3,4]))

	let filter_derived = (predicate, list) => reduce((acc, next) => predicate(next) ? [...acc, next] : acc, [], list);

	console.log("filter_derived(x=>x>2,[1,2,3,4,5]) :", filter(x=>x>2,[1,2,3,4,5]))