patterns: sort dictionary keys during analysis

src/syndicate/patterns.nim

@@ -1,7 +1,7 @@
 # SPDX-FileCopyrightText: ☭ Emery Hemingway
 # SPDX-License-Identifier: Unlicense
 
-import std/[options, sequtils, tables, typetraits]
+import std/[algorithm, options, sequtils, tables, typetraits]
 
 import preserves
 import ./protocols/dataspacePatterns
@@ -10,6 +10,7 @@ from ./actors import Ref
 export dataspacePatterns.`$`, PatternKind, DCompoundKind, AnyAtomKind
 
 type
+  Value = Preserve[Ref]
   AnyAtom = dataspacePatterns.AnyAtom[Ref]
   DBind = dataspacePatterns.DBind[Ref]
   DCompound = dataspacePatterns.DCompound[Ref]
@@ -19,6 +20,17 @@ type
   DLit = dataspacePatterns.DLit[Ref]
   Pattern* = dataspacePatterns.Pattern[Ref]
 
+iterator orderedEntries*(dict: DCompoundDict): (Value, Pattern) =
+  ## Iterate a `DCompoundDict` in Preserves order.
+  ## Values captured from a dictionary are represented as an
+  ## array of values ordered by their former key, so using an
+  ## ordered iterator is sometimes essential.
+  var keys = dict.entries.keys.toSeq
+  sort(keys, preserves.cmp)
+  for k in keys:
+    yield(k, dict.entries.getOrDefault(k))
+      # getOrDefault doesn't raise and we know the keys will match
+
 proc toPattern(d: sink DBind): Pattern =
   Pattern(orKind: PatternKind.DBind, dbind: d)
 
@@ -275,7 +287,6 @@ proc recordPattern*(label: Preserve[Ref], fields: varargs[Pattern]): Pattern =
   DCompoundRec(label: label, fields: fields.toSeq).toPattern
 
 type
-  Value = Preserve[Ref]
   Path* = seq[Value]
   Paths* = seq[Path]
   Captures* = seq[Value]
@@ -300,7 +311,7 @@ func walk(result: var Analysis; path: var Path; p: Pattern) =
     of DCompoundKind.arr:
        for k, e in p.dcompound.arr.items: walk(result, path, k, e)
     of DCompoundKind.dict:
-      for k, e in p.dcompound.dict.entries: walk(result, path, k, e)
+      for k, e in p.dcompound.dict.orderedEntries: walk(result, path, k, e)
   of PatternKind.DBind:
     result.capturePaths.add(path)
     walk(result, path, p.dbind.pattern)

tests/test_patterns.nim

@@ -20,3 +20,17 @@ test "patterns":
     have = capture(observerPat, observer).toPreserve(Ref).unpackLiterals
     want = [value.toPreserve(Ref)].toPreserve(Ref)
   check(have ==  want)
+
+type Record {.preservesDictionary.} = object
+  a, b, c: int
+
+test "dictionaries":
+  let pat = ?Record
+  echo pat
+  var source = initDictionary(Ref)
+  source["b".toSymbol(Ref)] = 2.toPreserve(Ref)
+  source["c".toSymbol(Ref)] = 3.toPreserve(Ref)
+  source["a".toSymbol(Ref)] = 1.toPreserve(Ref)
+
+  let values = capture(pat, source)
+  check $values == "@[1, 2, 3]"