Data commit

Task/Amb/F-Sharp/amb.fs

@@ -0,0 +1,28 @@
+// define the List "workflow" (monad)
+type ListBuilder() =
+   member o.Bind( lst, f ) = List.concat( List.map (fun x -> f x) lst )
+   member o.Return( x ) = [x]
+   member o.Zero() = []
+
+let list = ListBuilder()
+
+let amb = id
+
+// last element of a sequence
+let last s = Seq.nth ((Seq.length s) - 1) s
+
+// is the last element of left the same as the first element of right?
+let joins left right = last left = Seq.head right
+
+let example = list { let! w1 = amb ["the"; "that"; "a"]
+                     let! w2 = amb ["frog"; "elephant"; "thing"]
+                     let! w3 = amb ["walked"; "treaded"; "grows"]
+                     let! w4 = amb ["slowly"; "quickly"]
+                     if joins w1 w2 &&
+                        joins w2 w3 &&
+                        joins w3 w4
+                     then
+                        return String.concat " " [w1; w2; w3; w4]
+                   }
+
+printfn "%s" (List.head example)