1 files changed, 21 insertions, 2 deletions
diff --git a/2019/IntCode.hs b/2019/IntCode.hs
index 89b54a2..9e94066 100644
--- a/2019/IntCode.hs
+++ b/2019/IntCode.hs
@@ -1,7 +1,7 @@
 {-# LANGUAGE MultiParamTypeClasses, FlexibleInstances, FlexibleContexts #-}
 module IntCode (
-    IC(..),
-    parse, decode, run
+    Arg(..), IC(..),
+    parse, decode, run, unparse
 ) where
 
 import Control.Monad.ST
@@ -31,6 +31,25 @@ parse = map read . splitOn ','
                       (pre, _ : post) -> pre : splitOn c post
                       _ -> [s]
 
+unparse :: IC -> [Int]
+unparse ic = case ic of
+                 Add a b c -> go 1 [a,b,c]
+                 Mul a b c -> go 2 [a,b,c]
+                 Inp a     -> go 3 [a    ]
+                 Out a     -> go 4 [a    ]
+                 Jnz a b   -> go 5 [a,b  ]
+                 Jez a b   -> go 6 [a,b  ]
+                 Clt a b c -> go 7 [a,b,c]
+                 Ceq a b c -> go 8 [a,b,c]
+                 Hlt       -> [99]
+  where
+    go code as = (100 * mode as + code) : map bare as
+      where bare (Imm n) = n
+            bare (Addr n) = n
+    mode [] = 0
+    mode (Imm _ : as) = 1 + 10 * mode as
+    mode (Addr _ : as) = 10 * mode as
+
 decode :: [Int] -> (IC, Int)
 decode [] = error "IC: Execution fell off end of program"
 decode (ins : rest) =