add Hasher.reset and Hash.hashUnordered

crates/compiler/builtins/roc/Dict.roc

@@ -228,6 +228,7 @@ LowLevelHasher := { originalSeed : U64, state : U64 } has [
              addI64,
              addI128,
              complete,
+             reset,
          },
      ]
 
@@ -244,6 +245,9 @@ combineState = \@LowLevelHasher { originalSeed, state }, { a, b, seed, length }
 
 complete = \@LowLevelHasher { state } -> state
 
+reset = \@LowLevelHasher { originalSeed } ->
+    @LowLevelHasher { originalSeed, state: originalSeed }
+
 addI8 = \hasher, i8 ->
     addU8 hasher (Num.toU8 i8)
 addI16 = \hasher, i16 ->

crates/compiler/builtins/roc/Hash.roc

@@ -15,8 +15,10 @@ interface Hash
         addI64,
         addI128,
         complete,
+        reset,
         hashStrBytes,
         hashList,
+        hashUnordered,
     ] imports [
         List,
         Str,
@@ -73,6 +75,10 @@ Hasher has
     ## accumulated hash state.
     complete : a -> U64 | a has Hasher
 
+    ## Resets the internal state of a hasher
+    ## The hasher should still have all the same parameters and seeds.
+    reset : a -> a | a has Hasher
+
 ## Adds a string into a [Hasher] by hashing its UTF-8 bytes.
 hashStrBytes = \hasher, s ->
     addBytes hasher (Str.toUtf8 s)
@@ -82,22 +88,25 @@ hashList = \hasher, lst ->
     List.walk lst hasher \accumHasher, elem ->
         hash accumHasher elem
 
-# hashUnordered = \hasher, container, walk ->
-#     walk
-#         container
-#         0
-#         (\accum, elem ->
-#             x =
-#                 hasher
-#                 |> new
-#                 |> hash elem
-#                 |> complete
-#             nextAccum = Num.addWrap accum x
+## Adds a container of [Hash]able elements to a [Hasher] by hashing each element.
+## The container is iterated using the walk method passed in.
+## The order of the elements does not effect the final hash.
+hashUnordered = \hasher, container, walk ->
+    walk
+        container
+        0
+        (\accum, elem ->
+            x =
+                hasher
+                |> reset
+                |> hash elem
+                |> complete
+            nextAccum = Num.addWrap accum x
 
-#             if nextAccum < accum then
-#                 # we dont want to lose a bit of entropy on overflow, so add it back in.
-#                 Num.addWrap nextAccum 1
-#             else
-#                 nextAccum
-#         )
-#     |> \accum -> addU64 hasher accum
+            if nextAccum < accum then
+                # we dont want to lose a bit of entropy on overflow, so add it back in.
+                Num.addWrap nextAccum 1
+            else
+                nextAccum
+        )
+    |> \accum -> addU64 hasher accum

crates/compiler/module/src/symbol.rs

@@ -1530,8 +1530,10 @@ define_builtins! {
         12 HASH_ADD_I64: "addI64"
         13 HASH_ADD_I128: "addI128"
         14 HASH_COMPLETE: "complete"
-        15 HASH_HASH_STR_BYTES: "hashStrBytes"
-        16 HASH_HASH_LIST: "hashList"
+        15 HASH_RESET: "reset"
+        16 HASH_HASH_STR_BYTES: "hashStrBytes"
+        17 HASH_HASH_LIST: "hashList"
+        18 HASH_HASH_UNORDERED: "hashUnordered"
     }
     14 JSON: "Json" => {
         0 JSON_JSON: "Json"