Upsilon/Upsilon/Evaluator/Evaluator.cs

using System;
using System.Collections.Generic;
using System.Collections.Immutable;
using Upsilon.BaseTypes;
using Upsilon.BaseTypes.Number;
using Upsilon.Binder;
using Type = Upsilon.BaseTypes.Type;

namespace Upsilon.Evaluator
{
    internal class Evaluator
    {
        private readonly Diagnostics _diagnostics;
        private LuaType _lastValue;
        private LuaType _returnValue;
        internal EvaluationScope Scope { get; }
        private bool HasReturned { get; set; }

        internal Evaluator(Diagnostics diagnostics, Dictionary<VariableSymbol, LuaType> variables)
        {
            _diagnostics = diagnostics;
            Scope       = new EvaluationScope(variables);
        }

        private Evaluator(Diagnostics diagnostics, EvaluationScope parentScope)
        {
            _diagnostics = diagnostics;
            Scope        = new EvaluationScope(parentScope);
        }

        public LuaType Evaluate(BoundScript e)
        {
            Evaluate(e.Statement);
            if (_returnValue == null)
                return _lastValue;
            return _returnValue;
        }

        public LuaType Evaluate(BoundScript e, string functionName, ImmutableArray<LuaType> parameters)
        {
            Evaluate(e.Statement);
            if (!Scope.TryGet(functionName, out var statement) || statement.Type != Type.Function)
            {
                throw new ArgumentException(($"Function '{functionName}' could not be found"));
            }
            var function = (LuaFunction) statement;
            var innerEvaluator = new Evaluator(_diagnostics, Scope);
            for (var index = 0; index < parameters.Length; index++)
            {
                var parameter = parameters[index];
                var parameterName = function.Parameters[index];
                innerEvaluator.Scope.Set(parameterName, parameter);
            }

            var result = innerEvaluator.Evaluate(function.Block);
            return result;
        }

        private LuaType Evaluate(BoundNode b)
        {
            switch (b.Kind)
            {
                case BoundKind.BoundScript:
                    EvaluateStatement(((BoundScript)b).Statement);
                    break;
                case BoundKind.BoundLiteralExpression:
                case BoundKind.BoundBinaryExpression:
                case BoundKind.BoundUnaryExpression:
                case BoundKind.VariableExpression:
                case BoundKind.BoundFunctionCallExpression:
                    _lastValue = EvaluateExpression((BoundExpression) b);
                    break;
                case BoundKind.BoundAssignmentStatement:
                case BoundKind.BoundExpressionStatement:
                case BoundKind.BoundBlockStatement:
                case BoundKind.BoundIfStatement:
                case BoundKind.BoundElseStatement:
                case BoundKind.BoundFunctionStatement:
                case BoundKind.BoundPromise:
                    EvaluateStatement((BoundStatement) b);
                    break;
                default:
                    throw new ArgumentOutOfRangeException();
            }
            return _returnValue;
        }

        private void EvaluateStatement(BoundStatement e)
        {
            if (HasReturned)
                return;
            switch (e.Kind)
            {
                case BoundKind.BoundAssignmentStatement:
                    EvaluateAssignmentStatement((BoundVariableAssignment) e);
                    break;
                case BoundKind.BoundBlockStatement:
                    EvaluateBoundBlockStatement((BoundBlockStatement) e);
                    break;
                case BoundKind.BoundIfStatement:
                    EvaluateBoundIfStatement((BoundIfStatement) e);
                    break;
                case BoundKind.BoundFunctionStatement:
                    EvaluateBoundFunctionStatement((BoundFunctionStatement) e);
                    break;
                case BoundKind.BoundPromise:
                    EvaluateUnboundFunctionStatement((UnboundFunctionStatement) e);
                    break;
                case BoundKind.BoundReturnStatement:
                    EvaluateReturnStatement((BoundReturnStatement) e);
                    break;
                default:
                    EvaluateExpressionStatement((BoundExpressionStatement) e);
                    break;
            }
        }


        private void EvaluateExpressionStatement(BoundExpressionStatement e)
        {
            _lastValue = EvaluateExpression(e.Expression);
        }

        private LuaType EvaluateExpression(BoundExpression e)
        {
            switch (e.Kind)
            {
                case BoundKind.BoundLiteralExpression:
                    return ((BoundLiteralExpression) e).Value;
                case BoundKind.BoundBinaryExpression:
                    return EvaluateBinaryExpression((BoundBinaryExpression) e);
                case BoundKind.BoundUnaryExpression:
                    return EvaluateUnaryExpression((BoundUnaryExpression) e);
                case BoundKind.VariableExpression:
                    return EvaluateVariableExpression((BoundVariableExpression) e);
                case BoundKind.BoundFunctionCallExpression:
                    return EvaluateBoundFunctionCallExpression((BoundFunctionCallExpression) e);
                default:
                    throw new NotImplementedException();
            }
        }

        private LuaType EvaluateUnaryExpression(BoundUnaryExpression e)
        {
            var operand  = EvaluateExpression(e.InExpression);
            switch (e.Operator.Kind)
            {
                case BoundUnaryOperator.OperatorKind.Identity:
                    return operand;
                case BoundUnaryOperator.OperatorKind.Negation:
                    return -((Number)operand);
                case BoundUnaryOperator.OperatorKind.LogicalNegation:
                    return !(LuaBoolean) operand;
                default:
                    throw new Exception("Invalid Unary Operator: " + e.Operator.Kind);
            }
        }

        private LuaType EvaluateBinaryExpression(BoundBinaryExpression e)
        {
            var left  = EvaluateExpression(e.LeftExpression);
            var right = EvaluateExpression(e.RightExpression);
            switch (e.Operator.Kind)
            {
                case BoundBinaryOperator.OperatorKind.Addition:
                    return ((Number)left) + ((Number)right);
                case BoundBinaryOperator.OperatorKind.Subtraction:
                    return ((Number)left) - ((Number)right);
                case BoundBinaryOperator.OperatorKind.Multiplication:
                    return ((Number)left) * ((Number)right);
                case BoundBinaryOperator.OperatorKind.Division:
                    return ((Number)left) / ((Number)right);
                case BoundBinaryOperator.OperatorKind.Equality:
                    return new LuaBoolean(Equals(left, right));
                case BoundBinaryOperator.OperatorKind.Inequality:
                    return new LuaBoolean(!Equals(left, right));
                default:
                    throw new Exception("Invalid Binary Operator: " + e.Operator);
            }
        }

        private void EvaluateAssignmentStatement(BoundVariableAssignment e)
        {
            var val = EvaluateExpression(e.BoundExpression);
            if (e.Variable.Local)
            {
                Scope.Set(e.Variable, val);
            }
            else
            {
                Scope.SetGlobal(e.Variable, val);
            }
            _lastValue = val;
        }

        private LuaType EvaluateVariableExpression(BoundVariableExpression e)
        {
            if (Scope.TryGet(e.Variable, out var val))
            {
                return val;
            }
            throw new Exception($"Cannot find variable: '{e.Variable.Name}'");
        }

        private void EvaluateBoundBlockStatement(BoundBlockStatement boundBlockStatement)
        {
            foreach (var boundStatement in boundBlockStatement.Statements)
            {
                if (HasReturned)
                    return;
                EvaluateStatement(boundStatement);
            }
        }

        private void EvaluateBoundIfStatement(BoundIfStatement boundBlockStatement)
        {
            var innerEvaluator = new Evaluator(_diagnostics, Scope);
            var condition = innerEvaluator.EvaluateExpression(boundBlockStatement.Condition.Expression);
            if ((LuaBoolean) condition)
            {
                innerEvaluator.EvaluateStatement(boundBlockStatement.Block);
            }
            else if (boundBlockStatement.NextElseIf != null)
            {
                innerEvaluator.EvaluateStatement(boundBlockStatement.NextElseIf);
            }
            else if (boundBlockStatement.ElseStatement != null)
            {
                innerEvaluator.EvaluateStatement(boundBlockStatement.ElseStatement.Block);
            }
            HasReturned = innerEvaluator.HasReturned;
            if (HasReturned)
                _returnValue = innerEvaluator._returnValue;
            _lastValue = innerEvaluator._lastValue;
        }

        private void EvaluateBoundFunctionStatement(BoundFunctionStatement boundFunctionStatement)
        {
            var func = new LuaFunction(boundFunctionStatement.Parameters, boundFunctionStatement.Block);
            if (boundFunctionStatement.Identifier.Local)
                Scope.Set(boundFunctionStatement.Identifier, func);
            else
                Scope.SetGlobal(boundFunctionStatement.Identifier, func);
        }

        private void EvaluateUnboundFunctionStatement(UnboundFunctionStatement unboundFunctionStatement)
        {
            var func = new LuaFunction(unboundFunctionStatement.Parameters, unboundFunctionStatement.Block);
            if (unboundFunctionStatement.Identifier.Local)
                Scope.Set(unboundFunctionStatement.Identifier, func);
            else
                Scope.SetGlobal(unboundFunctionStatement.Identifier, func);

        }

        private LuaType EvaluateBoundFunctionCallExpression(BoundFunctionCallExpression boundFunctionCallExpression)
        {
            var name = boundFunctionCallExpression.Identifier;
            if (!Scope.TryGet(name, out var functionObj))
            {
                throw new Exception("Cannot find function: " + name.Name);
            }

            var function = (LuaFunction) functionObj;

            var innerEvaluator = new Evaluator(_diagnostics, Scope);
            for (var i = 0; i < function.Parameters.Length; i++)
            {
                var parameterVariable = function.Parameters[i];
                var parameterValue = innerEvaluator.EvaluateExpression(boundFunctionCallExpression.Parameters[i]);
                innerEvaluator.Scope.Set(parameterVariable, parameterValue);
            }
            _lastValue = innerEvaluator.Evaluate(function.Block);
            return _lastValue;
        }

        private void EvaluateReturnStatement(BoundReturnStatement b)
        {
            _returnValue = EvaluateExpression(b.Expression);
            _lastValue = _returnValue;
            HasReturned = true;
        }

    }
}