NTERA/NTERA.Interpreter/Interpreter.cs

using System;
using System.Collections.Generic;
using NTERA.Interpreter.Functions;

namespace NTERA.Interpreter
{
    public partial class Interpreter
    {
        public bool HasPrint { get; set; } = true;
        public bool HasInput { get; set; } = true;

        private Lexer lex;
        private Token prevToken;
        private Token lastToken;

        private Dictionary<string, Value> vars;
        private Dictionary<string, Marker> loops;

        public delegate Value BasicFunction(Interpreter interpreter, List<Value> args);
        private Dictionary<string, BasicFunction> funcs;

        private int ifcounter;

        private Marker lineMarker;

        private bool exit;

        public Interpreter(string input)
        {
            lex = new Lexer(input);
            vars = new Dictionary<string, Value>();
            loops = new Dictionary<string, Marker>();
            funcs = new Dictionary<string, BasicFunction>();
            ifcounter = 0;
            BuiltInFunctions.InstallAll(this);
        }

        public Value GetVar(string name)
        {
            if (!vars.ContainsKey(name))
                throw new Exception("Variable with name " + name + " does not exist.");
            return vars[name];
        }

        public void SetVar(string name, Value val)
        {
            if (!vars.ContainsKey(name)) vars.Add(name, val);
            else vars[name] = val;
        }

        public void AddFunction(string name, BasicFunction function)
        {
            if (!funcs.ContainsKey(name)) funcs.Add(name, function);
            else funcs[name] = function;
        }

        void Error(string text)
        {
            throw new Exception(text + " at line: " + lineMarker.Line);
        }

        void Match(Token tok)
        {
            if (lastToken != tok)
                Error("Expect " + tok + " got " + lastToken);
        }

        public void Exec()
        {
            exit = false;
            GetNextToken();
            while (!exit) Line();
        }

        Token GetNextToken()
        {
            prevToken = lastToken;
            lastToken = lex.GetToken();

            if (lastToken == Token.EOF && prevToken == Token.EOF)
                Error("Unexpected end of file");
            
            return lastToken;
        }

        void Line()
        {
            while (lastToken == Token.NewLine) GetNextToken();

            if (lastToken == Token.EOF)
            {
                exit = true;
                return;
            }

            lineMarker = lex.TokenMarker;
            Statment();

            if (lastToken != Token.NewLine && lastToken != Token.EOF)
                Error("Expect new line got " + lastToken);
        }

        void Statment()
        {
            Token keyword = lastToken;
            GetNextToken();
            switch (keyword)
            {
                case Token.Print: Print(); break;
                case Token.Input: Input(); break;
                case Token.If: If(); break;
                case Token.Else: Else(); break;
                case Token.EndIf: break;
                case Token.For: For(); break;
                case Token.Next: Next(); break;
                case Token.Let: Let(); break;
                case Token.End: End(); break;
                case Token.Identifer:
                    if (lastToken == Token.Equal) Let();
                    else goto default;
                    break;
                case Token.EOF:
                    exit = true;
                    break;
                default:
                    Error("Expect keyword got " + keyword);
                    break;
            }
            if (lastToken == Token.Colon)
            {
                GetNextToken();
                Statment();
            }
        }

        void Print()
        {
            if (!HasPrint)
                Error("Print command not allowed");

            Console.WriteLine(Expr().ToString());
        }

        void Input()
        {
            if (!HasInput)
                Error("Input command not allowed");

            while (true)
            {
                Match(Token.Identifer);
               
                if (!vars.ContainsKey(lex.Identifer)) vars.Add(lex.Identifer, new Value());
                
                string input = Console.ReadLine();
                double d;
                if (double.TryParse(input, System.Globalization.NumberStyles.Float, System.Globalization.CultureInfo.InvariantCulture, out d))
                    vars[lex.Identifer] = new Value(d);
                else
                    vars[lex.Identifer] = new Value(input);
                
                GetNextToken();
                if (lastToken != Token.Comma) break;
                GetNextToken();
            }
        }

        Value Expr()
        {
            Dictionary<Token, int> prec = new Dictionary<Token, int>() 
            {
                { Token.Or, 0 }, { Token.And, 0 },
                { Token.Equal, 1 }, { Token.NotEqual, 1 },       
                { Token.Less, 1 }, { Token.More, 1 }, { Token.LessEqual, 1 },  { Token.MoreEqual, 1 },
                { Token.Plus, 2 }, { Token.Minus, 2 },
                { Token.Asterisk, 3 }, {Token.Slash, 3 },
                { Token.Caret, 4 }
            };

            Stack<Value> stack = new Stack<Value>();
            Stack<Token> operators = new Stack<Token>();

            int i = 0;
            while (true)
            {
                if (lastToken == Token.Value)
                {
                    stack.Push(lex.Value);
                }
                else if (lastToken == Token.Identifer)
                {
                    if (vars.ContainsKey(lex.Identifer))
                    {
                        stack.Push(vars[lex.Identifer]);
                    }
                    else if (funcs.ContainsKey(lex.Identifer))
                    {
                        string name = lex.Identifer;
                        List<Value> args = new List<Value>();
                        GetNextToken();
                        Match(Token.LParen);

                        start:
                        if (GetNextToken() != Token.RParen)
                        {
                            args.Add(Expr());
                            if (lastToken == Token.Comma)
                                goto start;
                        }

                        stack.Push(funcs[name](null, args));
                    }
                    else
                    {
                        Error("Undeclared variable " + lex.Identifer);
                    }
                }
                else if (lastToken == Token.LParen)
                {
                    GetNextToken();
                    stack.Push(Expr());
                    Match(Token.RParen);
                }
                else if (lastToken >= Token.Plus && lastToken <= Token.Not)
                {
                    if ((lastToken == Token.Minus || lastToken == Token.Minus) && (i == 0 || prevToken == Token.LParen))
                    {
                        stack.Push(new Value(0));
                        operators.Push(lastToken);
                    }
                    else
                    {
                        while (operators.Count > 0 && prec[lastToken] <= prec[operators.Peek()])
                            Operation(ref stack, operators.Pop());
                        operators.Push(lastToken);
                    }
                }
                else
                {
                    if (i == 0)
                        Error("Empty expression");
                    break;
                }

                i++;
                GetNextToken();
            }

            while (operators.Count > 0)
                Operation(ref stack, operators.Pop());

            return stack.Pop();
        }

        void Operation(ref Stack<Value> stack, Token token)
        {
            Value b = stack.Pop();
            Value a = stack.Pop();
            Value result = a.BinOp(b, token);
            stack.Push(result);
        }
    }
}