public override LispNode Evaluate(Env env)
{
LispNode func = null;
LambdaNode lambdaNode = null;
func = What.Evaluate(env);
if (!(func is LambdaNode))
{
return(null);
}
lambdaNode = func as LambdaNode;
if (lambdaNode.Arguments.Count != Arguments.Count)
{
return(null);
}
Env newEnv = new Env(lambdaNode.Env); // use the lambda env, not the global env, for lexical closures
for (int i = 0; i < Arguments.Count; i++)
{
newEnv.Add(lambdaNode.Arguments[i], Arguments[i].Evaluate(env));
}
return(lambdaNode.Call(newEnv));
}
static LispNode Read(List <String> tokens)
{
if (tokens.Count() == 0)
{
return(null);
}
String token = tokens[0];
tokens.RemoveAt(0);
if (token == "(")
{
token = tokens[0];
if (token == "if")
{
tokens.RemoveAt(0);
IfNode ifNode = new IfNode();
ifNode.a = Read(tokens);
ifNode.b = Read(tokens);
ifNode.c = Read(tokens);
if (tokens[0] != ")")
{
return(null);
}
else
{
tokens.RemoveAt(0); // eat close paren
return(ifNode);
}
}
else if (token == "quote")
{
tokens.RemoveAt(0);
StringBuilder builder = new StringBuilder();
while (tokens[0] != ")")
{
builder.Append(tokens[0]);
tokens.RemoveAt(0);
}
QuoteNode quoteNode = new QuoteNode(builder.ToString());
tokens.RemoveAt(0);
return(quoteNode);
}
else if (token == "define")
{
tokens.RemoveAt(0);
String name = tokens[0];
tokens.RemoveAt(0);
LispNode expression = Read(tokens);
DefineNode defNode = new DefineNode(name, expression);
if (tokens[0] != ")")
{
return(null);
}
else
{
tokens.RemoveAt(0); // eat close paren
return(defNode);
}
}
else if (token == "begin")
{
tokens.RemoveAt(0);
BeginNode beginNode = new BeginNode();
do
{
beginNode.Expressions.Add(Read(tokens));
} while (tokens[0] != ")");
tokens.RemoveAt(0); // eat close paren
return(beginNode);
}
else if (token == "lambda")
{
tokens.RemoveAt(0);
LambdaNode lambdaNode = new LambdaNode();
if (tokens[0] != "(")
{
return(null);
}
tokens.RemoveAt(0);
while (tokens[0] != ")")
{
lambdaNode.Arguments.Add(tokens[0]);
tokens.RemoveAt(0);
}
tokens.RemoveAt(0);
lambdaNode.Body = Read(tokens);
tokens.RemoveAt(0);
return(lambdaNode);
}
else if (token == "set!")
{
tokens.RemoveAt(0);
SetNode setNode = new SetNode();
setNode.VariableName = tokens[0];
tokens.RemoveAt(0);
setNode.Expression = Read(tokens);
return(setNode);
}
else //if(token == "call")
{
CallNode callNode = new CallNode();
callNode.What = Read(tokens);
while (tokens[0] != ")")
{
callNode.Arguments.Add(Read(tokens));
}
tokens.RemoveAt(0);
return(callNode);
}
//return null;
}
else if (token == ")")
{
return(null);
}
else
{
return(ParseAtom(token));
}
}