KumiScript/interpreter/LispPrimitives.cs

namespace KumiScript.Interpreter
{
    public class LispPrimitives
    {
        public static Expression Lambda(ListExpression args, Environment env)
        {
            Expression car = args.Car();
            ListExpression rest = args.Cdr();

            ListExpression? head = car as ListExpression;
            if (head is null)
                throw new InterpreterInvalidDefinitionException();
            
            List<Expression> headl = head.GetMembers();
            List<Symbol> arg_names = new List<Symbol>();
            for (int i = 0; i < headl.Count; i++)
            {
                SymbolExpression? argi = headl[i] as SymbolExpression;
                if (argi is null)
                    throw new InterpreterInvalidDefinitionException();
                
                arg_names.Add(argi.GetSymbol());
            }

            Expression body = rest.Car();
            return new ProcedureExpression(new LispProcedure(arg_names, body, env));
        }

        public static NumberExpression Plus(ListExpression args, Environment env)
        {
            List<Expression> argl = args.EvalMembers(env);
            decimal acc = 0;
            for (int i = 0; i < argl.Count; i++)
            {
                NumberExpression? argin = argl[i] as NumberExpression;
                if (argin is null)
                    throw new InterpreterTypingException();

                acc += argin.GetValueAsFloat();
            }

            return NumberFactory.NormalizeFloat(acc);
        }

        public static NumberExpression Minus(ListExpression args, Environment env)
        {
            List<Expression> argl = args.EvalMembers(env);
            if (argl.Count == 0)
                throw new InterpreterInvalidApplicationException();

            NumberExpression? argn0 = argl[0] as NumberExpression;
            if (argn0 is null)
                throw new InterpreterTypingException();

            decimal acc = argn0.GetValueAsFloat();
            if (argl.Count == 1)
                return NumberFactory.NormalizeFloat(1 - acc);
            
            for (int i = 1; i < argl.Count; i++)
            {
                NumberExpression? argin = argl[i] as NumberExpression;
                if (argin is null)
                    throw new InterpreterTypingException();
                
                acc -= argin.GetValueAsFloat();
            }
            return NumberFactory.NormalizeFloat(acc);
        }

        public static NumberExpression Times(ListExpression args, Environment env)
        {
            List<Expression> argl = args.EvalMembers(env);
            if (argl.Count < 2)
                throw new InterpreterInvalidInvocationException();
            
            NumberExpression? arg0 = argl[0] as NumberExpression;
            if (arg0 is null)
                throw new InterpreterTypingException();

            decimal f = arg0.GetValueAsFloat();
            for (int i = 1; i < argl.Count; i++)
            {
                NumberExpression? argn = argl[i] as NumberExpression;
                if (argn is null)
                    throw new InterpreterTypingException();
                
                f *= argn.GetValueAsFloat();
            }
            return NumberFactory.NormalizeFloat(f);
        }

        public static NumberExpression DividedBy(ListExpression args, Environment env)
        {
            List<Expression> argl = args.EvalMembers(env);
            if (argl.Count != 2)
                throw new InterpreterInvalidApplicationException();

            NumberExpression? arg0 = argl[0] as NumberExpression;
            if (arg0 is null)
                throw new InterpreterTypingException();

            NumberExpression? arg1 = argl[1] as NumberExpression;
            if (arg1 is null)
                throw new InterpreterTypingException();
            
            return NumberFactory.NormalizeFloat(arg0.GetValueAsFloat() / arg1.GetValueAsFloat());
        }

        public static NumberExpression Modulus(ListExpression args, Environment env)
        {
            List<Expression> argl = args.EvalMembers(env);
            if (argl.Count != 2)
                throw new InterpreterInvalidApplicationException();

            NumberExpression? arg0 = argl[0] as NumberExpression;
            if (arg0 is null)
                throw new InterpreterTypingException();

            NumberExpression? arg1 = argl[1] as NumberExpression;
            if (arg1 is null)
                throw new InterpreterTypingException();
            
            return NumberFactory.NormalizeFloat(arg0.GetValueAsFloat() % arg1.GetValueAsFloat());
        }


        public static Expression Quote(ListExpression args, Environment env)
        {
            List<Expression> argl = args.GetMembers();
            if (argl.Count != 1)
                throw new InterpreterInvalidApplicationException();
            
            return argl[0];
        }

        public static Expression Define(ListExpression args, Environment env)
        {
            List<Expression> argl = args.GetMembers();
            if (argl.Count != 2)
                throw new InterpreterInvalidApplicationException();
            
            SymbolExpression? binding = argl[0] as SymbolExpression;
            if (binding is null)
                throw new InterpreterTypingException();
            
            Symbol name = binding.GetSymbol();            
            Expression definition = argl[1].Eval(env);
            env.AddSymbol(name, definition);
            
            return definition;
        }

        public static Expression Car(ListExpression args, Environment env)
        {
            List<Expression> argl = args.EvalMembers(env);
            if (argl.Count != 1)
                throw new InterpreterInvalidApplicationException();
            
            ListExpression? list = argl[0] as ListExpression;
            if (list is null)
                throw new InterpreterTypingException();
            
            return list.Car();
        }

        public static ListExpression Cdr(ListExpression args, Environment env)
        {
            List<Expression> argl = args.EvalMembers(env);
            if (argl.Count != 1)
                throw new InterpreterInvalidApplicationException();
            
            ListExpression? list = argl[0] as ListExpression;
            if (list is null)
                throw new InterpreterTypingException();
            
            return list.Cdr();
        }

        public static ProperListExpression Cons(ListExpression args, Environment env)
        {
            List<Expression> argl = args.EvalMembers(env);
            if (argl.Count != 2)
                throw new InterpreterInvalidApplicationException();

            Expression car = argl[0];
            ListExpression? cdr = argl[1] as ListExpression;
            if (cdr is null)
                throw new InterpreterTypingException();
            
            return cdr.Cons(car);
        }

        public static Expression Quit(ListExpression args, Environment env)
        {
            System.Environment.Exit(0);
            return new SymbolExpression(new Symbol("bye"));
        }

        public static Expression Cond(ListExpression args, Environment env)
        {
            List<Expression> argl = args.GetMembers();
            for (int i = 0; i < argl.Count; i ++)
            {
                ProperListExpression? conditional = argl[i] as ProperListExpression;
                if (conditional is null)
                    throw new InterpreterTypingException();
                
                Expression antecedent = conditional.Car();
                Expression consequent = conditional.Cdr().Car();
                if (!(antecedent.Eval(env) is NilExpression))
                    return consequent.Eval(env);
            }
            return NilExpression.GetInstance();
        }

        public static Expression Eq(ListExpression args, Environment env)
        {
            List<Expression> argl = args.EvalMembers(env);
            if (argl.Count != 2)
                throw new InterpreterInvalidApplicationException();
            
            if (argl[0].Equals(argl[1]))
                return TrueExpression.GetInstance();
            
            return NilExpression.GetInstance();
        }

        public static Expression Set(ListExpression args, Environment env)
        {
            List<Expression> argl = args.GetMembers();
            if (argl.Count != 2)
                throw new InterpreterInvalidApplicationException();

            SymbolExpression? binding = argl[0] as SymbolExpression;
            if (binding is null)
                throw new InterpreterTypingException();

            Symbol name = binding.GetSymbol();            
            Expression definition = argl[1].Eval(env);
            env.RedefineSymbol(name, definition);

            return definition;
        }

        public static Environment RegisterPrimitives()
        {
            Environment result = new Environment();
            result.AddSymbol(new Symbol("lambda"), new ProcedureExpression(new PrimitiveProcedure(Lambda)));
            result.AddSymbol(new Symbol("quote"), new ProcedureExpression(new PrimitiveProcedure(Quote)));
            result.AddSymbol(new Symbol("define"), new ProcedureExpression(new PrimitiveProcedure(Define)));
            result.AddSymbol(new Symbol("car"), new ProcedureExpression(new PrimitiveProcedure(Car)));
            result.AddSymbol(new Symbol("cdr"), new ProcedureExpression(new PrimitiveProcedure(Cdr)));
            result.AddSymbol(new Symbol("cons"), new ProcedureExpression(new PrimitiveProcedure(Cons)));
            result.AddSymbol(new Symbol("quit"), new ProcedureExpression(new PrimitiveProcedure(Quit)));
            result.AddSymbol(new Symbol("cond"), new ProcedureExpression(new PrimitiveProcedure(Cond)));
            result.AddSymbol(new Symbol("+"), new ProcedureExpression(new PrimitiveProcedure(Plus)));
            result.AddSymbol(new Symbol("-"), new ProcedureExpression(new PrimitiveProcedure(Minus)));
            result.AddSymbol(new Symbol("*"), new ProcedureExpression(new PrimitiveProcedure(Times)));
            result.AddSymbol(new Symbol("/"), new ProcedureExpression(new PrimitiveProcedure(DividedBy)));
            result.AddSymbol(new Symbol("%"), new ProcedureExpression(new PrimitiveProcedure(Modulus)));
            result.AddSymbol(new Symbol("eq"), new ProcedureExpression(new PrimitiveProcedure(Eq)));
            result.AddSymbol(new Symbol("set!"), new ProcedureExpression(new PrimitiveProcedure(Set)));

            return result;
        }
    }
}