This online REPL does not support `let` either.
`let x = 4` is not an expression there.
`let x = 4` is not an expression there.
let primes = sieve [2..] where sieve (p:xs) = p : sieve [x| x <- xs, x `mod` p /= 0] in primes
Which is rather annoying. let primes = ... in take 5 primes
... if you want the computation to complete without hanging the browser. It would be nice if the REPL supported multi-line expressions.