Data commit

Task/Fractran/Julia/fractran.julia

@@ -0,0 +1,37 @@
+# FRACTRAN interpreter implemented as an iterable struct
+
+using .Iterators: filter, map, take
+import Base: iterate, show
+
+struct Fractran
+    rs::Vector{Rational{BigInt}}
+    i₀::BigInt
+end
+
+iterate(f::Fractran, i = f.i₀) =
+    for r in f.rs
+        if iszero(i % r.den) # faster than isinteger(i*r)
+            i = i ÷ r.den * r.num
+            return (i, i)
+        end
+    end
+
+run(f::Fractran) = map(trailing_zeros, filter(ispow2, f))
+
+show(io::IO, f::Fractran) = join(io, take(run(f), 30), ' ')
+
+macro code_str(s)
+   eval(Meta.parse("[" * replace(s, "/" => "//") * "]"))
+end
+
+# Example FRACTRAN program generating primes
+primes = Fractran(code"17/91, 78/85, 19/51, 23/38, 29/33, 77/29, 95/23,
+        77/19, 1/17, 11/13, 13/11, 15/14, 15/2, 55/1", 2)
+
+# Output
+println("First 25 iterations of FRACTRAN program 'primes':\n2 ",
+    join(take(primes, 25), ' '))
+
+println("\nWatch the first 30 primes dropping out within seconds:")
+
+primes