internal override Value Copy()
{
var res = new LambdaFuncValue(Formals.Copy() as QExprValue, Body.Copy())
{
Environment = Environment.Copy()
};
return(res);
}
internal static Value Call(Env environment, FuncValue function, SExprValue arguments)
{
BuiltinFuncValue builtin = function.As <BuiltinFuncValue>();
LambdaFuncValue lambda = function.As <LambdaFuncValue>();
// If Builtin then simply call that
if (builtin != null)
{
return(builtin.BuiltinFunction(environment, arguments));
}
// Record Argument Counts
int given = arguments.Cell.Count;
int total = lambda.Formals.Cell.Count;
// While arguments still remain to be processed
while (arguments.Cell.Count > 0)
{
// If we've ran out of formal arguments to bind
if (lambda.Formals.Cell.Count == 0)
{
return(new ErrorValue($"Function passed too many arguments. Got {given}, Expected {total}."));
}
// Pop the first symbol from the formals
SymbolValue symbol = lambda.Formals.Cell[0].As <SymbolValue>();
lambda.Formals.Cell.RemoveAt(0);
// Special Case to deal with '&'
if (symbol.Value == "&")
{
// Ensure '&' is followed by another symbol
if (lambda.Formals.Cell.Count != 1)
{
return(new ErrorValue("Function format invalid. Symbol '&' not followed by single symbol."));
}
// Next formal should be bound to remaining arguments.
SymbolValue nsym = lambda.Formals.Cell[0].As <SymbolValue>();
lambda.Formals.Cell.RemoveAt(0);
lambda.Environment.Put(nsym.Value, Builtins.List(environment, arguments));
break;
}
// Pop the next argument from the list
Value val = arguments.Cell[0];
arguments.Cell.RemoveAt(0);
// Bind a copy into the function's environment
lambda.Environment.Put(symbol.Value, val);
}
// Argument list is now bound.
// if '&' remains in formal list after we've bound arguments then bind to empty list
if (lambda.Formals.Cell.Count > 0 &&
lambda.Formals.Cell[0].As <SymbolValue>().Value == "&")
{
// check to ensure that & is not passed invalidly.
if (lambda.Formals.Cell.Count != 2)
{
return(new ErrorValue("Function format invalid. Symbol '&' not followed by single symbol."));
}
// Pop and throw away '&' symbol
lambda.Formals.Cell.RemoveAt(0);
// Pop next symbol and create empty list
SymbolValue symbolValue = lambda.Formals.Cell[0].As <SymbolValue>();
lambda.Formals.Cell.RemoveAt(0);
QExprValue val = new QExprValue();
// Bind to environment and delete
lambda.Environment.Put(symbolValue.Value, val);
}
// If all formals have been bound evaluate
if (lambda.Formals.Cell.Count == 0)
{
// Set environment parent to evaluation environment
lambda.Environment.Parent = environment;
// Evaluate and return
var sexpr = new SExprValue();
sexpr.Cell.Add(lambda.Body.Copy());
return(Builtins.Eval(lambda.Environment, sexpr));
}
else
{
// Otherwise return partially evaluated function
return(lambda.Copy());
}
}
