Um… new to SML, still getting my feet wet.

MRE:

Exception Failure

fun knapsack(0,xs) = 0
  | knapsack(a,[]) = raise Failure
  | knapsack(a,(x,y)::xs) =
                if x > a then
                        knapsack(a,xs)
                else
                        x+knapsack(a-x,xs)

fun main() =
        let
                val l = [(20, 9), (17, 8), (14, 7), (10, 6), (8, 5), (6, 3)]
                val c = 20
        in
                knapsack(c,l)
        end

Error:

knapsack.sml:1.2 Error: syntax error: inserting  INFIX
/usr/lib/smlnj/bin/sml: Fatal error -- Uncaught exception Compile with "syntax error" raised at ../compiler/Parse/main/smlfile.sml:15.24-15.46

I’m guessing the :: operator is the culprit, but I can’t figure out what is wrong.