Expression ParseAtom()
{
string id;
Expression x = null;
FunctionDefinition fnDef = null;
switch (_token.Type)
{
// literals
case TKTYPE.LITERAL:
x = new Expression(_observer, _token);
break;
// identifiers
case TKTYPE.IDENTIFIER:
// get identifier
id = (string)_token.Value;
// look for functions
if (_fnTbl.TryGetValue(id, out fnDef))
{
var p = GetParameters();
var pCnt = p == null ? 0 : p.Count;
if (fnDef.ParmMin != -1 && pCnt < fnDef.ParmMin)
{
Throw("Too few parameters.");
}
if (fnDef.ParmMax != -1 && pCnt > fnDef.ParmMax)
{
Throw("Too many parameters.");
}
x = new FunctionExpression(_observer, fnDef, p);
break;
}
// look for simple variables (much faster than binding!)
if (_vars.ContainsKey(id))
{
x = new VariableExpression(_observer, _vars, id);
break;
}
// look for external objects
var xObj = GetExternalObject(id);
if (xObj != null)
{
x = new XObjectExpression(_observer, xObj);
break;
}
// look for bindings
if (DataContext != null)
{
var list = new List <BindingInfo>();
for (var t = _token; t != null; t = GetMember())
{
list.Add(new BindingInfo((string)t.Value, GetParameters()));
}
x = new BindingExpression(_observer, this, list, _ci);
break;
}
Throw("Unexpected identifier: " + id);
break;
// sub-expressions
case TKTYPE.GROUP:
// anything other than opening parenthesis is illegal here
if (_token.ID != TKID.OPEN)
{
Throw("Expression expected.");
}
// get expression
GetToken();
x = ParseCompare();
// check that the parenthesis was closed
if (_token.ID != TKID.CLOSE)
{
Throw("Unbalanced parenthesis.");
}
break;
}
// make sure we got something...
if (x == null)
{
Throw();
}
// done
GetToken();
return(x);
}
public FunctionExpression(FunctionDefinition function, List <Expression> parms)
{
_fn = function;
_parms = parms;
}