private IEnumerable <ExecutionMessage> SLet(List <SExpression> args, Environment e)
{
Environment local = new Environment(e); //TODO BUG: (let () ...) parses the name name bindings that are the pair <EmptyList,NULL>
if (args[0] is SPair)
{
SPair nameBindings = (SPair)args[0];
if (!nameBindings.isProperList())
{
throw new Exception("Can't use impro per list in a let");
}
List <SExpression> names = nameBindings.flatten();
for (int i = 0; i < names.Count - 1; i++)
{
String name = ((SID)((SPair)names[i]).getHead()).identifier;
SExpression val = ((SPair)((SPair)names[i]).getTail()).getHead();
//Cycle through the yields until done
var elmEnum = evaluate(val, e).GetEnumerator();
SExpression elm = null;
while (elmEnum.MoveNext())
{
ExecutionMessage current = elmEnum.Current;
if (current.status == ExecStatus.DONE)
{
elm = current.returnVal; break;
}
yield return(current);
}
local.addVal(name, elm);
}
}
else if (args[0] is SEmptyList)
{
}
else
{
throw new Exception("Name bindings section of let must be a list");
}
//Lets can have an arbitrary number of statements after the name bindings, execute them for stateful effects
ExecutionMessage msg = null;
for (int i = 1; i < args.Count; i++)
{
foreach (var tmsg in evaluate(args[i], local))
{
msg = tmsg;
if (msg.status == ExecStatus.DONE)
{
continue;
}
yield return(msg);
}
}
//yield final message
yield return(msg);
}
public SFunc(SID arglst, SExpression body, Environment e)
{
arglist = arglst;
names = null;
//our starting environment is the env we were defined in
env = new Environment(e);
env.addVal(arglist.identifier, new SNone()); //add bound variables to environment with default None value
fixedArgCount = false;
this.body = body;
}
public SExpression body; //body of execution
public SFunc(List <SID> names, SExpression body, Environment e)
{
//our starting environment is the env we were defined in
arglist = null;
env = new Environment(e);
foreach (SID id in names)
{
env.addVal(id.identifier, new SNone()); //add bound variables to environment with default None value
}
this.names = names;
this.body = body;
fixedArgCount = true;
argCount = names.Count;
}
private IEnumerable <ExecutionMessage> SDefine(List <SExpression> args, Environment e)
{
if (e.hasParent())
{
throw new Exception("Define only allowed at global scope");
}
SID name = (SID)args[0];
ExecutionMessage msg = null;
foreach (var tmsg in evaluate(args[1], e))
{
msg = tmsg;
if (msg.status == ExecStatus.DONE)
{
break;
}
yield return(msg);
}
e.addVal(name.identifier, msg.returnVal);
yield return(new ExecutionMessage(ExecStatus.DONE, new SNone()));
}
public DerpInterpreter()
{
callStack = new List <SExpression>();
e = new Environment();
parser = new DerpParser("");
e.addVal("+", new SPrimitive(SAdd, false, 0));
e.addVal("*", new SPrimitive(SMult, false, 0));
e.addVal("/", new SPrimitive(SDiv, true, 2));
e.addVal("-", new SPrimitive(SSub, false, 0));
e.addVal("mod", new SPrimitive(SMod, true, 2));
e.addVal("if", new SPrimitive(SIf, true, 3, false));
e.addVal("let", new SPrimitive(SLet, false, 0, false));
e.addVal("define", new SPrimitive(SDefine, true, 2, false));
e.addVal("lambda", new SPrimitive(SLambda, true, 2, false));
e.addVal("debug", new SPrimitive(SDebug, true, 1));
e.addVal("list", new SPrimitive(SList, false, 0));
e.addVal("cons", new SPrimitive(SCons, true, 2));
e.addVal("car", new SPrimitive(SCar, true, 1));
e.addVal("cdr", new SPrimitive(SCdr, true, 1));
e.addVal("null?", new SPrimitive(SNullList, true, 1));
e.addVal("=", new SPrimitive(SEq, true, 2));
e.addVal(">", new SPrimitive(SGt, true, 2));
e.addVal("<", new SPrimitive(SLt, true, 2));
e.addVal("begin", new SPrimitive(SBegin, false, 0));
e.addVal("typeof", new SPrimitive(TypeOf, false, 1));
e.addVal("eval", new SPrimitive(Eval, false, 1));
}