private If(Expr lhExpr, Relop relop, Expr rhExpr, Statement statement)
{
this.lhExpr = lhExpr;
this.relop = relop;
this.rhExpr = rhExpr;
this.statement = statement;
}
public static If Parse(Input input, TextWriter output)
{
return(input.RewindOnNull(() =>
{
var cmd = input.Pop(KeywordIf);
if (cmd == null)
{
return null;
}
var lhExpr = Expr.Parse(input, output);
if (lhExpr == null)
{
output.WriteLine(MessageFormatter.Expected("expression"));
return null;
}
var relop = Relop.Parse(input);
if (relop == null)
{
output.WriteLine(MessageFormatter.Expected(Relop.Strings));
return null;
}
var rhExpr = Expr.Parse(input, output);
if (rhExpr == null)
{
output.WriteLine(MessageFormatter.Expected("expression"));
return null;
}
var then = input.Pop(KeywordThen);
if (then == null)
{
output.WriteLine(MessageFormatter.Expected(KeywordThen));
return null;
}
var statement = Statement.Parse(input, output);
if (statement == null)
{
output.WriteLine(MessageFormatter.Expected("statement"));
return null;
}
return new If(lhExpr, relop, rhExpr, statement);
}));
}