hope: A non-pure functional language

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  1. Functional with strict typed.
  2. Polymorphic type using typever.
  3. Example: Calculate prime numbers by sieve of Eratosthenes. 

    ! Lazy prime number generation in HOPE
dec from : num -> list num;
--- from n <= n ::: from succ (n);

dec filter : num # list num -> list num;
--- filter (x, y :: ys) <=
	if y mod x = 0 then
		filter (x, ys)
	else
		y ::: filter (x, ys);

dec sieve : list num -> list num;
--- sieve (x :: xs) <= x ::: sieve filter (x, xs);

dec upto : num # list num -> list num;
--- upto (e, x :: xs) <= if e < x then [] else x :: upto (e, xs);

dec primes : num -> list num;
--- primes n <= upto (n, sieve (from 2));

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