1 files changed, 179 insertions, 0 deletions
diff --git a/code/Interpreter/Parser.java b/code/Interpreter/Parser.java
new file mode 100644
index 0000000..6b55299
--- /dev/null
+++ b/code/Interpreter/Parser.java
@@ -0,0 +1,179 @@
+package Interpreter;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Parser {
+    private final List<Token> tokens;
+    private int currentToken = 0;
+
+    Parser(List<Token> tokens){
+        this.tokens=tokens;
+    }
+
+    List<Statement> parse(){
+        List<Statement> statements =  new ArrayList<>();
+        while (!checkEOF()){
+            statements.add(declaration());
+        }
+        return statements;
+        
+    }
+
+    private Statement declaration(){
+        try{
+            if (matchAndAdvance(TokenType.VAR)){
+                if (matchOrError(TokenType.DEFINE, ":: Required for variable definition")){
+                    if (matchOrError(TokenType.IDENTIFIER,"Expected variable name.")){
+                        Token varName = getPreviousToken();
+                        return new Statement.VariableDeclaration(varName);
+                    } 
+                }
+            }
+            return statement();
+        } catch (Error e){
+            currentToken++;
+            return null;
+        }
+    }
+
+    private Statement statement(){
+        if (matchAndAdvance(TokenType.PRINT)){
+            Expression expression = expression();
+            return new Statement.PrintStatement(expression);
+        }
+        return expressionStatement();
+    }
+
+
+
+    private Statement expressionStatement(){
+        Expression expression = assignment();
+        return new Statement.ExpressionStatement(expression);
+    }
+
+    private Expression assignment(){
+        Expression variable = expression();
+        if (matchAndAdvance(TokenType.EQUALS)){
+            Expression assignedvalue = expression();
+
+            if (variable instanceof Expression.Variable){
+                return new Expression.AssignmentExpression(((Expression.Variable)variable).name,assignedvalue);
+            }
+            throw error("Incorrect assignment operation");
+        }
+        return variable;
+    }
+
+    private Expression expression(){
+        Expression createdExpression = equality();
+        return createdExpression;
+    }
+
+    private Expression equality(){
+        Expression createdExpression = comparison();
+        while (matchAndAdvance(TokenType.EQUALITY)){
+            Token op = getPreviousToken();
+            Expression right = comparison();
+            createdExpression = new Expression.Binary(createdExpression, op, right);
+        }
+        return createdExpression;
+    }
+
+    private Expression comparison(){
+        Expression createdExpression = term();
+        while (matchAndAdvance(TokenType.GREATER)||matchAndAdvance(TokenType.LESS)){
+            Token op = getPreviousToken();
+            Expression right = term();
+            createdExpression = new Expression.Binary(createdExpression, op, right);
+        }
+        return createdExpression;
+    }
+
+    private Expression term(){
+        Expression createdExpression = factor();
+        while (matchAndAdvance(TokenType.PLUS)||matchAndAdvance(TokenType.MINUS)){
+            Token op = getPreviousToken();
+            Expression right = factor();
+            createdExpression = new Expression.Binary(createdExpression, op, right);
+        }
+        return createdExpression;
+    }
+
+    private Expression factor(){
+        Expression createdExpression = primary();
+        while (matchAndAdvance(TokenType.STAR)||matchAndAdvance(TokenType.SLASH)){
+            Token op = getPreviousToken();
+            Expression right = primary();
+            createdExpression = new Expression.Binary(createdExpression, op, right);
+        }
+        return createdExpression;
+    }
+
+    private Expression primary(){
+        if (matchAndAdvance(TokenType.NUMBER)){
+            return new Expression.Literal(getPreviousToken());
+        }
+
+        if (matchAndAdvance(TokenType.IDENTIFIER)) {
+
+            return new Expression.Variable(getPreviousToken());
+          }
+
+        if (matchAndAdvance(TokenType.LEFT_PAREN)){
+            Expression expr = expression();
+            if (matchAndAdvance(TokenType.RIGHT_PAREN)){
+                return new Expression.BracketedExpression(expr);
+            }
+            else{
+                throw error("Expected ')");
+            }
+        }
+        throw error("Expected Expression");
+    }
+
+    private void advanceToken(){
+        if (!checkEOF()) {
+            currentToken++;
+        };
+    }
+
+    private boolean matchAndAdvance(TokenType type){
+        if (checkToken(type)) {
+            advanceToken();
+            return true;
+        }
+        return false;
+    }
+
+    private boolean matchOrError(TokenType type,String errorMessage){
+        if (matchAndAdvance(type)){
+            return true;
+        }
+        throw error(errorMessage);
+    }
+
+    private boolean checkToken(TokenType type){
+        if (checkEOF()) return false;
+        return getCurrentToken().type == type; 
+    }
+
+    private boolean checkEOF(){
+        return tokens.get(currentToken).type==TokenType.EOF;
+    }
+
+    private Token getCurrentToken(){
+        return tokens.get(currentToken);
+    }
+
+    private Token getPreviousToken(){
+        return tokens.get(currentToken - 1);
+    }
+
+    private Error error(String message){
+        Language.displayError(message);
+        return new Error();
+    }
+
+
+}