From 0cf83eff62600496e07b571ebe6a875bea01688f Mon Sep 17 00:00:00 2001
From: LPeter1997 <lenkefi.peti@gmail.com>
Date: Thu, 5 Oct 2023 10:09:06 +0200
Subject: [PATCH] Update DecisionTree.cs

---
 .../Internal/FlowAnalysis/DecisionTree.cs     | 20 +++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/src/Draco.Compiler/Internal/FlowAnalysis/DecisionTree.cs b/src/Draco.Compiler/Internal/FlowAnalysis/DecisionTree.cs
index 6c23a59d4..924f50eb2 100644
--- a/src/Draco.Compiler/Internal/FlowAnalysis/DecisionTree.cs
+++ b/src/Draco.Compiler/Internal/FlowAnalysis/DecisionTree.cs
@@ -154,8 +154,24 @@ private SpecializationComparer()
     /// <param name="matchedValue">The matched value.</param>
     /// <param name="arms">The arms of the match.</param>
     /// <returns>The constructed decision tree.</returns>
-    public static DecisionTree<TAction> Build(BoundExpression matchedValue, ImmutableArray<Arm> arms) =>
-        throw new NotImplementedException();
+    public static DecisionTree<TAction> Build(BoundExpression matchedValue, ImmutableArray<Arm> arms)
+    {
+        // Construct root
+        var root = new MutableNode(
+            parent: null,
+            arguments: new List<BoundExpression> { matchedValue },
+            patternMatrix: arms
+                .Select(a => new List<BoundPattern> { a.Pattern })
+                .ToList(),
+            actions: arms
+                .Select(a => a.Action)
+                .ToList());
+        // Wrap in the tree
+        var tree = new DecisionTree<TAction>(root);
+        // Build it
+        tree.Build(root);
+        return tree;
+    }
 
     /// <summary>
     /// Stringifies the given <paramref name="pattern"/> to a user-readable format.