Higher order array methods

anArray.forEach(fn(e,i))

.map(f(e,i)→r) → array of rs

.every(f(e,i)→boolean) → boolean // ∀

.some(f(e,i)→boolean) → boolean // ∃

.filter(f(e,i)→boolean) → subset

.reduce(f(r,e,i)→r, r?) → r

.reduceRight(f(r,e,i)→r, r?) → r