Add Stream Sieve benchmark from Typed Racket

Closes #427.

benchmarks/streamSieve/lua.lua

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+-- Naive stream-based prime sieve benchmark. (Based on a typed-racket benchmark)
+-- Based on https://github.com/bennn/gtp-benchmarks/tree/master/benchmarks/sieve
+
+local m = {}
+
+----------------------------------------------
+
+-- Simple streams library for building infinite lists.
+-- A stream is a cons of a value and a thunk that computes the next value.
+
+
+
+-- TODO: with recursive types, this could be (any -> Stream)
+
+
+local function make_stream(first, rest)
+    return {first=first, rest=rest}
+end
+
+local function stream_head(st)
+    return st.first
+end
+
+local function stream_tail(st)
+    return st.rest()
+end
+
+local function stream_get(st, n)
+    for _ = 1, n-1 do
+        st = stream_tail(st)
+    end
+    return stream_head(st)
+end
+
+----------------------------------------------
+
+-- Build a stream of integers starting from 1
+local function count_from(n)
+    return make_stream(n, function() return count_from(n+1) end)
+end
+
+-- Filter all multiples of n
+local function sift(n, st)
+    local hd = stream_head(st)
+    local tl = stream_tail(st)
+    if hd % n == 0 then
+        return sift(n, tl)
+    else
+        return make_stream(hd, function() return sift(n, tl) end)
+    end
+end
+
+-- Naive sieve of Erasthostenes
+local function sieve(st)
+    local hd = stream_head(st)
+    local tl = stream_tail(st)
+    return make_stream(hd, function() return sieve(sift(hd, tl)) end)
+end
+
+----
+
+function m.get_prime(n)
+    local primes = sieve(count_from(2))
+    return stream_get(primes, n)
+end
+
+return m

benchmarks/streamSieve/main.lua

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+--
+-- This benchmark runs a naive prime sieve using lazy streams. Taken from the
+-- Typed Racket benchmarks:
+--  * https://github.com/nuprl/gradual-typing-performance/tree/master/benchmarks/sieve
+--  * https://github.com/bennn/gtp-benchmarks/tree/master/benchmarks/sieve
+--
+
+local sieve = require(arg[1])
+local N     = tonumber(arg[2]) or 2000 -- or 5500
+
+print(string.format("primes(%d) = %d", N, sieve.get_prime(N)))

benchmarks/streamSieve/pallene.pln

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+-- Naive stream-based prime sieve benchmark. (Based on a typed-racket benchmark)
+-- Based on https://github.com/bennn/gtp-benchmarks/tree/master/benchmarks/sieve
+
+local m = {}
+
+----------------------------------------------
+
+-- Simple streams library for building infinite lists.
+-- A stream is a cons of a value and a thunk that computes the next value.
+
+record Stream
+    first: any
+    rest: () -> any -- TODO: with recursive types, this could be (any -> Stream)
+end
+
+local function make_stream(first: any, rest: ()->any): Stream
+    return {first=first, rest=rest}
+end
+
+local function stream_head(st: Stream): any
+    return st.first
+end
+
+local function stream_tail(st: Stream): Stream
+    return st.rest() as Stream
+end
+
+local function stream_get(st: Stream, n: integer): any
+    for _ = 1, n-1 do
+        st = stream_tail(st)
+    end
+    return stream_head(st)
+end
+
+----------------------------------------------
+
+-- Build a stream of integers starting from 1
+local function count_from(n: integer): Stream
+    return make_stream(n, function() return count_from(n+1) end)
+end
+
+-- Filter all multiples of n
+local function sift(n: integer, st: Stream): Stream
+    local hd = stream_head(st) as integer
+    local tl = stream_tail(st) as Stream
+    if hd % n == 0 then
+        return sift(n, tl)
+    else
+        return make_stream(hd, function() return sift(n, tl) end)
+    end
+end
+
+-- Naive sieve of Erasthostenes
+local function sieve(st: Stream): Stream
+    local hd = stream_head(st) as integer
+    local tl = stream_tail(st) as Stream
+    return make_stream(hd, function() return sieve(sift(hd, tl)) end)
+end
+
+----
+
+function m.get_prime(n: integer): integer
+    local primes = sieve(count_from(2))
+    return stream_get(primes, n)
+end
+
+return m