Upsilon/Upsilon/Binder/Binder.cs

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

namespace Upsilon.Binder
{
    internal class Binder
    {
        private readonly Diagnostics _diagnostics;
        public BoundScope Scope { get; private set; }

        private Dictionary<FunctionVariableSymbol, UnboundFunctionStatement> _unboundFunctions =
            new Dictionary<FunctionVariableSymbol, UnboundFunctionStatement>();

        public Binder(Diagnostics diagnostics, Dictionary<VariableSymbol, LuaType> variables)
        {
            _diagnostics = diagnostics;
            Scope = new BoundScope(variables, null);
        }

        public BoundScript BindScript(BlockStatementSyntax e)
        {
            var bound = BindStatement(e);
            foreach (var unboundFunctionStatement in _unboundFunctions)
            {
                Scope = new BoundScope(Scope);
                foreach (var valueParameter in unboundFunctionStatement.Value.Parameters)
                {
                    Scope.SetVariable(valueParameter);
                }
                unboundFunctionStatement.Value.Block =
                    (BoundBlockStatement) BindBlockStatement(unboundFunctionStatement.Value.UnboundBlock);
                Scope                                      = Scope.ParentScope;
                unboundFunctionStatement.Key.IsBound = true;
            }
            _unboundFunctions = new Dictionary<FunctionVariableSymbol, UnboundFunctionStatement>();
            return new BoundScript((BoundBlockStatement) bound);
        }

        private BoundStatement BindStatement(StatementSyntax s)
        {
            switch (s.Kind)
            {
                case SyntaxKind.ExpressionStatement:
                    return BindExpressionStatement((ExpressionStatementSyntax) s);
                case SyntaxKind.AssignmentStatement:
                    return BindAssignmentStatement((AssignmentExpressionSyntax) s);
                case SyntaxKind.BlockStatement:
                    return BindBlockStatement((BlockStatementSyntax) s);
                case SyntaxKind.IfStatement:
                    return BindIfStatement((IfStatementSyntax) s);
                case SyntaxKind.FunctionStatement:
                    return BindFunctionStatement((FunctionStatementSyntax) s);
                case SyntaxKind.ReturnStatement:
                    return BindReturnStatement((ReturnStatementSyntax) s);
            }

            throw new NotImplementedException(s.Kind.ToString());
        }

        private BoundExpression BindExpression(ExpressionSyntax e)
        {
            switch (e.Kind)
            {
                case SyntaxKind.UnaryExpression:
                    return BindUnaryExpression((UnaryExpressionSyntax) e);
                case SyntaxKind.BinaryExpression:
                    return BindBinaryExpression((BinaryExpressionSyntax) e);
                case SyntaxKind.LiteralExpression:
                    return BindLiteralExpression((LiteralExpressionSyntax) e);
                case SyntaxKind.ParenthesizedExpression:
                    return BindParenthesizedExpression((ParenthesizedExpressionSyntax) e);
                case SyntaxKind.VariableExpression:
                    return BindVariableExpression((VariableExpressionSyntax) e);
                case SyntaxKind.FunctionCallExpression:
                    return BindFunctionCallExpression((FunctionCallExpressionSyntax) e);
                case SyntaxKind.BadExpression:
                    break;
                case SyntaxKind.ScriptUnit:
                    break;
                default:
                    throw new ArgumentOutOfRangeException();
            }
            throw new NotImplementedException(e.Kind.ToString());
        }

        private BoundExpression BindUnaryExpression(UnaryExpressionSyntax e)
        {
            var inExp  = BindExpression(e.Expression);
            var op    = BoundUnaryOperator.Bind(e.Operator.Kind, inExp.Type);
            if (op == null)
            {
                _diagnostics.LogUnknownUnaryOperator(e.Span, e.Operator.Kind, inExp.Type);
                return inExp;
            }

            return new BoundUnaryExpression(op, inExp, op.OutType);
        }

        private BoundExpression BindBinaryExpression(BinaryExpressionSyntax e)
        {
            var left = BindExpression(e.Left);
            var right = BindExpression(e.Right);
            var op = BoundBinaryOperator.Bind(e.Operator.Kind, left.Type, right.Type);
            if (op == null)
            {
                _diagnostics.LogUnknownBinaryOperator(e.Span, e.Operator.Kind, left.Type, right.Type);
                return left;
            }
            return new BoundBinaryExpression(op, left, right, op.OutType);
        }

        private BoundExpression BindLiteralExpression(LiteralExpressionSyntax e)
        {
            var value = e.Value;
            LuaType outValue = null;
            switch (value)
            {
                case double d:
                    outValue = new NumberDouble(d);
                    break;
                case long l:
                    outValue = new NumberLong(l);
                    break;
                case bool b:
                    outValue = new LuaBoolean(b);
                    break;
                case null:
                    outValue = new LuaNull();
                    break;
                default:
                    _diagnostics.LogUnknownType(e.Span);
                    break;
            }
            return new BoundLiteralExpression(outValue);
        }

        private BoundExpression BindParenthesizedExpression(ParenthesizedExpressionSyntax e)
        {
            return BindExpression(e.Expression);
        }

        private BoundExpression BindFunctionCallExpression(FunctionCallExpressionSyntax e)
        {
            var name = e.Identifier.Name;
            if (!Scope.TryGetVariable(name, true, out var functionObj))
            {
                _diagnostics.LogUnknownVariable(e.Identifier.Span, name);
                return new BoundLiteralExpression(new LuaNull());
            }

            var function = (FunctionVariableSymbol) functionObj;

            var parameters = ImmutableArray.CreateBuilder<BoundExpression>();
            foreach (var expressionSyntax in e.Parameters)
            {
                var bound = BindExpression(expressionSyntax);
                parameters.Add(bound);
            }

            if (!function.IsBound)
            {
                Scope = new BoundScope(Scope);
                for (var index = 0; index < function.Parameters.Length; index++)
                {
                    var functionVariable = function.Parameters[index];
                    var callingVariable = parameters[index];
                    functionVariable.Type = callingVariable.Type;
                    Scope.SetVariable(functionVariable);
                }

                var unboundFunctionStatement = _unboundFunctions[function];
                unboundFunctionStatement.Block =
                    (BoundBlockStatement) BindBlockStatement(unboundFunctionStatement.UnboundBlock);
                Scope = Scope.ParentScope;
                function.IsBound = true;
                _unboundFunctions.Remove(function);
            }

            //TODO: validate parameters
            return new BoundFunctionCallExpression(function, parameters.ToImmutable());
        }

        private BoundExpression BindVariableExpression(VariableExpressionSyntax e)
        {
            var name = e.Identifier.Name;
            if (!Scope.TryGetVariable(name, true, out var variable))
            {
                _diagnostics.LogUnknownVariable(e.Identifier.Span, name);
                return new BoundLiteralExpression(new LuaNull());
            }

            return new BoundVariableExpression(variable);
        }

        private BoundStatement BindExpressionStatement(ExpressionStatementSyntax s)
        {
            var exp = BindExpression(s.Expression);
            return new BoundExpressionStatement(exp);
        }

        private BoundStatement BindAssignmentStatement(AssignmentExpressionSyntax e)
        {
            var name            = e.Identifier.Name;
            var boundExpression = BindExpression(e.Expression);

            var isLocal = e.LocalToken != null;
            if (!Scope.TryGetVariable(name, !isLocal, out var variable))
            {
                variable = new VariableSymbol(name, boundExpression.Type, isLocal);
                if (isLocal)
                    Scope.SetVariable(variable);
                else
                    Scope.SetGlobalVariable(variable);
            }
            else
            {
                // don't allow assigning different typed variables to a variable, unless either of them is nil, allow assigning nil to all variables
                if (boundExpression.Type != variable.Type)
                {
                    if (variable.Type == Type.Nil || boundExpression.Type == Type.Nil)
                    {
                        variable.Type = boundExpression.Type;
                    }
                    else if (variable.Type == Type.Unknown)
                    {
                        variable.Type = boundExpression.Type;
                    }
                    else if (boundExpression.Type == Type.Unknown && boundExpression is BoundVariableExpression v)
                    {
                        v.Variable.Type = variable.Type;
                    }
                    else
                    {
                        _diagnostics.LogCannotConvert(boundExpression.Type, variable.Type, e.Span);
                        return new BoundExpressionStatement(boundExpression);
                    }
                }
            }

            return new BoundVariableAssignment(variable, boundExpression);
        }


        private BoundStatement BindBlockStatement(BlockStatementSyntax e)
        {
            var arr = ImmutableArray.CreateBuilder<BoundStatement>();
            foreach (var statementSyntax in e.Statements)
            {
                var bound = BindStatement(statementSyntax);
                arr.Add(bound);
            }

            return new BoundBlockStatement(arr.ToImmutable());
        }

        private BoundStatement BindIfStatement(IfStatementSyntax e)
        {
            Scope = new BoundScope(Scope);
            var condition = BindExpressionStatement(e.Condition);
            var block = BindBlockStatement(e.Block);
            Scope = Scope.ParentScope;
            if (e.NextElseIfStatement != null)
            {
                var nextElseIf = BindIfStatement(e.NextElseIfStatement);
                return new BoundIfStatement((BoundExpressionStatement) condition, (BoundBlockStatement) block,
                    (BoundIfStatement) nextElseIf);
            }
            if (e.ElseStatement == null)
            {
                return new BoundIfStatement((BoundExpressionStatement) condition, (BoundBlockStatement) block);
            }
            else
            {
                Scope = new BoundScope(Scope);
                var elseBlock = BindBlockStatement(e.ElseStatement.Block);
                var elseStatement = new BoundElseStatement((BoundBlockStatement) elseBlock);
                Scope = Scope.ParentScope;

                return new BoundIfStatement((BoundExpressionStatement) condition, (BoundBlockStatement) block,
                    elseStatement);
            }
        }

        private BoundStatement BindFunctionStatement(FunctionStatementSyntax e)
        {
            var name = e.Identifier.Name;
            var isLocal = e.LocalToken != null;

            var innerScope = new BoundScope(Scope);
            var parameters = ImmutableArray.CreateBuilder<VariableSymbol>();
            foreach (var identifierToken in e.Parameters)
            {
                var vari = new VariableSymbol(identifierToken.Name, Type.Unknown, true);
                parameters.Add(vari);
                innerScope.SetVariable(vari);
            }

            if (!Scope.TryGetVariable(name, !isLocal, out var variable))
            {
                variable = new FunctionVariableSymbol(name, Type.Function, isLocal, parameters.ToImmutable());
                if (isLocal)
                    Scope.SetVariable(variable);
                else
                    Scope.SetGlobalVariable(variable);
            }
            else
            {
                // don't allow assigning different typed variables to a variable, unless either of them is nil, allow assigning nil to all variables
                if (variable.Type != Type.Function)
                {
                    if (variable.Type == Type.Nil )
                    {
                        variable.Type = Type.Function;
                    }
                    else
                    {
                        _diagnostics.LogCannotConvert(Type.Function, variable.Type, e.Span);
                        return new BoundExpressionStatement(null);
                    }
                }
            }

            if (parameters.Count == 0)
            {
                Scope = innerScope;
                var block = BindBlockStatement(e.Block);
                Scope = Scope.ParentScope;
                ((FunctionVariableSymbol) variable).IsBound = true;
                var func = new BoundFunctionStatement(variable, parameters.ToImmutable(), (BoundBlockStatement) block);
                return func;
            }
            else
            {
                var unbound = new UnboundFunctionStatement(variable, parameters.ToImmutable(), e.Block);
                _unboundFunctions.Add((FunctionVariableSymbol) variable, unbound);
                return unbound;
            }
        }

        private BoundStatement BindReturnStatement(ReturnStatementSyntax e)
        {
            var expression = BindExpression(e.Expression);
            return new BoundReturnStatement(expression);
        }

    }
}