From 0afb650d149a0ff9dcc9777c0ec041c533b136b4 Mon Sep 17 00:00:00 2001
From: Maël Gassmann <mael.gassmann@students.bfh.ch>
Date: Sat, 12 Jun 2021 14:25:57 +0200
Subject: [~] First working version of the JavaCC calculator

---
 calculator-javacc/Calculator.jj | 136 +++++++++++++++++++++++++++++++---------
 1 file changed, 106 insertions(+), 30 deletions(-)

diff --git a/calculator-javacc/Calculator.jj b/calculator-javacc/Calculator.jj
index 9222654..cc22b0a 100644
--- a/calculator-javacc/Calculator.jj
+++ b/calculator-javacc/Calculator.jj
@@ -1,48 +1,40 @@
 options{
     //DEBUG_PARSER = true; DEBUG_TOKEN_MANAGER = true;
-    STATIC=false;
 }
 
 PARSER_BEGIN(Calculator)
-import java.util.Scanner;
-import java.io.StringReader;
+import java.util.HashMap;
 
 public class Calculator {
 
-    private static double currentNumber;
-
-    public static double fromString(String stringToParse) throws ParseException{
-        currentNumber = 0.0;
-
-        Calculator parser = new Calculator(new StringReader(stringToParse));
-        parser.parse();
-        return currentNumber;
-    }
+    private static HashMap variables = new HashMap();
 
     public static void main(String[] args) {
-        Scanner scanner = new Scanner(System.in);
+        Calculator parser = new Calculator(System.in);
         while (true){
             System.out.print("Type your expression: ");
-            String expression = scanner.nextLine();
             try{
-                System.out.println("Returned: " + fromString(expression));
-            }catch (Throwable t){
-                System.out.println(t);
+                double value = parser.evaluateNextLine();
+                System.out.println("Returned: " + value);
+            }catch (ParseException e){
+                System.out.println(e.getMessage());
+                try{
+                    parser.passStatement(); // wiping the tokens of the malformed expression
+                }catch (ParseException ex){
+                    System.out.println(ex.getMessage());
+                }
             }
         }
     }
 }
 PARSER_END(Calculator)
 
-/**
-* For now only using the Hello World grammar
-*/
-
 SKIP : {
-    " "|"\t"|"\n"|"\r"
+    " "|"\t"
 }
 
 TOKEN : {
+	<EOL: "\n"|"\r">|
 	<PAL: "(">|
 	<PAR: ")">|
 	<ADD: "+">|
@@ -56,24 +48,108 @@ TOKEN : {
 	<ID: (["a"-"z"]|["A"-"Z"])+>
 }
 
+double statement() :
+{
+    Token id;
+    double i = 0.0;
+}
+{
+    <END> { System.exit(0); }|
+    i=expression() { return i; }|
+    <LET> id=<ID> <EQU> i=expression()
+        {
+            variables.put(id.image,i); //Storing the variable
+            return i;
+        }
+}
+
+double expression() :
+{
+    Token op = null;
+    double l = 0.0;
+    double r = 0.0;
+}
+{
+    l=term() ((op=<ADD> | op=<SUB>)  r=term()
+        { // folding everything in the l variable
+            if (op != null){
+                if (op.image.equals("+"))
+                    l += r;
+                else
+                    l -= r;
+            }
+
+        }
+        )*
+        { //returning the parsed value
+            return l;
+        }
+}
+
+double term() :
+{
+    Token op = null;
+    double l = 0.0;
+    double r = 0.0;
+}
+{
+    l=factor() ((op=<DIV> | op=<MUL>)  r=factor()
+        { // folding everything in the l variable
+            if (op != null){
+                if (op.image.equals("/"))
+                    l /= r;
+                else
+                    l *= r;
+            }
 
+        }
+        )*
+        { //returning the parsed value
+            return l;
+        }
+}
 
 double factor() :
 {
-    Token t;
-    double i;
+    Token t = null;
+    Token id = null;
+    double i = 0.0;
 }
 {
-    t = <NUM>
+    (t=<NUM> | id=<ID> | <PAL> (i=expression())? <PAR>)
         {
-            i = Double.parseDouble(t.image);
-            currentNumber += i;
+            if(id != null){
+                Object var = variables.get(id.image);
+                if (var != null)
+                    i = (double) var;
+                else
+                    throw new ParseException("'" + id.image + "' is not yet defined.");
+            }else if(t != null)
+                i = Double.parseDouble(t.image);
             return i;
-        }
+        }|
+    <SUB> (t=<NUM> | id=<ID> | <PAL> (i=expression())? <PAR>)
+    {
+            if(id != null){
+                i = (double)variables.get(id.image);
+            }else if(t != null)
+                i = Double.parseDouble(t.image);
+        return i*(-1);
+    }
 }
 
-void parse() : {
+double evaluateNextLine() :
+{
+    double result = 0.0;
+}
+{
+	(result=statement())? <EOL> {return result;}|
+	<EOF>{System.out.println("\nBuffer was closed. Exiting."); System.exit(0);}
 }
+
+void passStatement() :
+{}
 {
-	(factor())* <EOF>
+    <EOL>|
+	<EOF>{System.out.println("\nBuffer was closed. Exiting."); System.exit(0);}
 }
\ No newline at end of file
-- 
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