static public Cell Eval(Cell x, Env env)
{
if (x.Type == Cell.CellType.Undefined)
{
throw new Exception("Undefined cell type");
}
// Symbol
if (x.Type == Cell.CellType.Symbol)
{
return(env[x.symbol]);
}
// Number
else if (x.Type != Cell.CellType.List)
{
return(x);
}
// List
if (x.list[0].symbol == "begin")
{
Cell res = null;
foreach (var exp in x.list.Skip(1))
{
res = Eval(exp, env);
}
return(res);
}
else if (x.list[0].symbol == "quote")
{
return(x.list[1]);
}
else if (x.list[0].symbol == "if")
{
var test = x.list[1];
var conseq = x.list[2];
var alt = x.list[3];
var exp = (Eval(test, env).boolval) == true ? conseq : alt;
return(Eval(exp, env));
}
else if (x.list[0].symbol == "define")
{
var variable = x.list[1];
var exp = x.list[2];
env[variable.symbol] = Eval(exp, env);
return(null);
}
else if (x.list[0].symbol == "set!")
{
env[x.list[1].symbol] = Eval(x.list[2], env);
return(null);
}
else if (x.list[0].symbol == "lambda")
{
return(new Cell()
{
proc = new Procedure(x.list[1], x.list[2], env), Type = Cell.CellType.Procedure
});
}
else
{
var proc = Eval(x.list[0], env);
var args = x.list.Skip(1).Select(n => Eval(n, env)).ToList();
if (proc.Type == Cell.CellType.Procedure)
{
// Lambda call
return(proc.proc.Call(args));
}
else
{
// Function call
return((Cell)proc.func.DynamicInvoke(args));
}
}
}
public Procedure(Cell parms, Cell body, Env env)
{
this.parms = parms.list.Select(x => x.symbol).ToList();
this.body = body;
this.env = env;
}
public Cell Call(List <Cell> args)
{
Env localEnv = new Env(parms, args, env);
return(Program.Eval(body, localEnv));
}