KumiScript/interpreter/LispPrimitives.cs

using KumiScript.Reader;

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

            List<Expression> headl = car.GetMembers();
            List<Symbol> arg_names = new List<Symbol>();
            for (int i = 0; i < headl.Count; i++)
            {
                arg_names.Add(headl[i].GetSymbol());
            }

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

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

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

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

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

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

            Expression car = argl[0];
            Expression cdr = argl[1];
            return cdr.Cons(car);
        }

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

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

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

            Symbol name = argl[0].GetSymbol();            
            Expression definition = argl[1].Eval(env);
            env.RedefineSymbol(name, definition);
            return definition;
        }

        public static Expression For(Expression args, Environment env)
        {
            List<Expression> argl = args.GetMembers();
            if (argl.Count != 4)
                throw new InterpreterInvalidApplicationException();

            Expression init = argl[0];
            Expression cond = argl[1];
            Expression step = argl[2];
            Expression body = argl[3];
            Expression result = NilExpression.GetInstance();
            Environment inner = new Environment(env);

            for (init.Eval(inner); cond.Eval(inner) != NilExpression.GetInstance(); step.Eval(inner))
                result = body.Eval(inner);
            
            return result;
        }

        public static Expression Progn(Expression args, Environment env)
        {
            List<Expression> argl = args.GetMembers();
            Expression result = NilExpression.GetInstance();

            foreach (Expression expr in argl)
                result = expr.Eval(env);
                
            return result;
        }

        public static Expression Prog1(Expression args, Environment env)
        {
            List<Expression> argl = args.GetMembers();
            Expression result = argl.Count > 0 ? argl[0] : NilExpression.GetInstance();

            foreach (Expression expr in argl)
                expr.Eval(env);
            
            return result;
        }

        public static Expression Not(Expression args, Environment env)
        {
            List<Expression> argl = args.EvalMembers(env);
            if (argl.Count != 1)
                throw new InterpreterInvalidApplicationException();

            return argl[0] != NilExpression.GetInstance() ? NilExpression.GetInstance() : TrueExpression.GetInstance();
        }

        public static Expression Nth(Expression args, Environment env)
        {
            List<Expression> argl = args.EvalMembers(env);
            if (argl.Count != 2)
                throw new InterpreterInvalidApplicationException();
            
            int n = (int) argl[0].GetValueAsFloat();
            List<Expression> arg1l = argl[1].GetMembers();
            return n >= 0 && n < arg1l.Count ? arg1l[n] : NilExpression.GetInstance();
        }

        public static Expression While(Expression args, Environment env)
        {
            List<Expression> argl = args.GetMembers();
            if (argl.Count != 2)
                throw new InterpreterInvalidApplicationException();
            
            Expression cond = argl[0];
            Expression body = argl[1];
            Expression result = NilExpression.GetInstance();
            Environment inner = new Environment(env);

            while (cond.Eval(inner) != NilExpression.GetInstance())
                result = body.Eval(inner);
            
            return result;
        }

        public static Environment RegisterPrimitives()
        {
            Environment result = new Environment();
            result.AddSymbol(SymbolTable.GetInstance().FromString("lambda"), new ProcedureExpression(new PrimitiveProcedure(Lambda)));
            result.AddSymbol(SymbolTable.GetInstance().FromString("quote"), new ProcedureExpression(new PrimitiveProcedure(Quote)));
            result.AddSymbol(SymbolTable.GetInstance().FromString("define"), new ProcedureExpression(new PrimitiveProcedure(Define)));
            result.AddSymbol(SymbolTable.GetInstance().FromString("car"), new ProcedureExpression(new PrimitiveProcedure(Car)));
            result.AddSymbol(SymbolTable.GetInstance().FromString("cdr"), new ProcedureExpression(new PrimitiveProcedure(Cdr)));
            result.AddSymbol(SymbolTable.GetInstance().FromString("cons"), new ProcedureExpression(new PrimitiveProcedure(Cons)));
            result.AddSymbol(SymbolTable.GetInstance().FromString("quit"), new ProcedureExpression(new PrimitiveProcedure(Quit)));
            result.AddSymbol(SymbolTable.GetInstance().FromString("cond"), new ProcedureExpression(new PrimitiveProcedure(Cond)));
            result.AddSymbol(SymbolTable.GetInstance().FromString("eq"), new ProcedureExpression(new PrimitiveProcedure(Eq)));
            result.AddSymbol(SymbolTable.GetInstance().FromString("set!"), new ProcedureExpression(new PrimitiveProcedure(Set)));
            result.AddSymbol(SymbolTable.GetInstance().FromString("for"), new ProcedureExpression(new PrimitiveProcedure(For)));
            result.AddSymbol(SymbolTable.GetInstance().FromString("progn"), new ProcedureExpression(new PrimitiveProcedure(Progn)));
            result.AddSymbol(SymbolTable.GetInstance().FromString("not"), new ProcedureExpression(new PrimitiveProcedure(Not)));
            result.AddSymbol(SymbolTable.GetInstance().FromString("prog1"), new ProcedureExpression(new PrimitiveProcedure(Prog1)));
            result.AddSymbol(SymbolTable.GetInstance().FromString("nth"), new ProcedureExpression(new PrimitiveProcedure(Nth)));
            result.AddSymbol(SymbolTable.GetInstance().FromString("while"), new ProcedureExpression(new PrimitiveProcedure(While)));
            return result;
        }
    }
}