Day 8 in Standard ML

Author: hypirion

days/day-08/solutions/day08.sml

@@ -0,0 +1,65 @@
+use "../../../util.sml";
+
+local
+    structure IS = IntSet
+in
+
+datatype Op = ACC | JMP | NOP
+
+fun opFromString "acc" = ACC
+  | opFromString "jmp" = JMP
+  | opFromString "nop" = NOP
+  | opFromString s = raise Fail $ "opFromString - bad input: " ^ s
+
+fun toInstruction s =
+    case String.tokens (fn c => c = #" ") s of
+        [a, b] => (opFromString a, valOf $ Int.fromString b)
+      | _  => raise Fail $ "bad input: " ^ s
+
+datatype TerminationReason = STOPPED of int
+                           | INF_LOOP of int
+
+fun programResult (STOPPED n) = n
+  | programResult (INF_LOOP n) = n
+
+fun run (program : (Op * int) RList.Coll) : TerminationReason =
+    let fun go seen pc acc =
+            if IS.contains pc seen then
+                INF_LOOP acc
+            else if RList.size program <= pc then
+                STOPPED acc
+            else
+                let val seen' = IS.insert pc seen
+                in
+                case RList.get (pc, program) of
+                    (ACC, n) => go seen' (pc + 1) (acc + n)
+                  | (JMP, n)  => go seen' (pc + n) acc
+                  | (NOP, _) => go seen' (pc + 1) acc
+                end
+    in
+        go IS.empty 0 0
+    end
+
+fun flip (ACC, n) = NONE
+  | flip (JMP, n) = SOME (NOP, n)
+  | flip (NOP, n) = SOME (JMP, n)
+
+fun findFlip program i =
+    case flip $ RList.get (i, program) of
+        NONE => findFlip program (i+1)
+      | SOME newOp =>
+        case run (RList.set (i, newOp, program)) of
+            INF_LOOP _ => findFlip program (i+1)
+          | STOPPED n => n
+
+fun main () =
+    let val program = TextIO.inputAll TextIO.stdIn
+                                      >> String.tokens (fn c => c = #"\n")
+                                      >> List.map toInstruction
+                                      >> RList.fromList
+    in
+        println $ Int.toString $ programResult $ run program;
+        println $ Int.toString $ findFlip program 0
+    end
+    handle Subscript => println "boo"
+end

days/day-08/test.sh

@@ -6,5 +6,6 @@ D=$(dirname $(realpath $0))
 
 echo ""
 echo "--- Day 8: Handheld Halting ---"
+$D/../../languages/sml.sh    $D/input.txt $D/output.txt $D/solutions/day08.sml
 $D/../../languages/deno.sh   $D/input.txt $D/output.txt $D/solutions/day08.ts
 echo ""

util.sml

@@ -227,3 +227,11 @@ structure StringMap = Map(
     end)
 
 structure StringSet = Set(StringMap)
+
+structure IntMap = Map(
+    struct
+    type t = int
+    val cmp = Int.compare
+    end)
+
+structure IntSet = Set(IntMap)