From a5026d325484c53fca75a561da5fcd39cbc84239 Mon Sep 17 00:00:00 2001
From: fredrikr79 <fredrikrobertsen7@gmail.com>
Date: Thu, 18 Sep 2025 06:54:06 +0200
Subject: [PATCH] expressiontree

---
 assignment2/main.oz | 27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/assignment2/main.oz b/assignment2/main.oz
index a5697e4..e2279c8 100644
--- a/assignment2/main.oz
+++ b/assignment2/main.oz
@@ -30,7 +30,7 @@ local
             [] number(N)|Tail then
                 {Aux Tail N|Stack}
             [] operator(type:Op)|Tail then % operators are binary (arity 2)
-                case Stack of Y|X|StackTail then
+                case Stack of X|Y|StackTail then
                     {Aux Tail (case Op
                         of plus then X + Y
                         [] minus then X - Y  
@@ -57,4 +57,29 @@ local
         end
         in {Aux Tokens nil} % this is where Interpret starts
     end
+
+
+    % this is just a stripped down Interpret. it resembles the shunting-yard algorithm
+    fun {ExpressionTree Tokens}
+        fun {ExpressionTreeInternal Tokens ExpressionStack}
+            case Tokens of
+                nil then ExpressionStack
+            [] number(N)|Tail then
+                {ExpressionTreeInternal Tail N|ExpressionStack}
+            [] operator(type:Op)|Tail then
+                case ExpressionStack of X|Y|ExpressionStackTail then
+                    {ExpressionTreeInternal Tail (case Op
+                        % return the tree records rather than the arithmetic result of the operators
+                        of plus then plus(X Y)
+                        [] minus then minus(X Y)
+                        [] multiply then multiply(X Y)
+                        [] divide then divide(X Y)
+                        else raise unexpectedOperator end end
+                    )|ExpressionStackTail}  
+                else raise stackUnderflow end end
+            else raise unexpectedToken end end
+        end
+        in {ExpressionTreeInternal Tokens nil} % this is where ExpressionTree starts
+    end
+    {Show {Interpret {Tokenize {Lex "3 10 9 * - 7 +"}}}}
 end
\ No newline at end of file