// comparison : identifier comparison_op param_value
private Expression Comparison()
{
using (var lookahead = _tokenzier.BeginLookahead())
{
var sourceLocation = _tokenzier.CurrentLocation;
var paramName = _tokenzier.NextToken();
if (paramName == null)
{
return(null);
}
if (paramName.Kind != TokenKind.Identifier)
{
_context.AddError("Expected identifier.", sourceLocation);
return(null);
}
sourceLocation = _tokenzier.CurrentLocation;
var op = _tokenzier.NextToken();
if (op == null || (op.Kind != TokenKind.ComparisonOperator && op.Kind != TokenKind.Identifier) || !_context.RegisteredComparisonOperators.Contains(op.Value))
{
_context.AddError("Missing comparison operator after the parameter name.", sourceLocation);
return(null);
}
sourceLocation = _tokenzier.CurrentLocation;
var value = ComparisonValue();
if (value == null)
{
_context.AddError("Missing parameter value.", sourceLocation);
return(null);
}
lookahead.Accept();
var param = new ComparisonParamExpression(paramName.Value);
return(new ComparisonExpression(param, value, op.Value));
}
}
protected override sealed void Visit(ComparisonParamExpression exp)
{
WriteParamName(exp.ParamName);
}
protected sealed override void Visit(ComparisonParamExpression exp)
{
WriteParamName(exp.ParamName);
}
