public static Let Parse(Input input, TextWriter output)
{
return(input.RewindOnNull(() =>
{
if (input.Pop(Keyword) == null)
{
return null;
}
var var = Var.Parse(input, output);
if (var == null)
{
output.WriteLine(MessageFormatter.Expected("var"));
return null;
}
if (input.Pop("=") == null)
{
output.WriteLine(MessageFormatter.Expected("="));
return null;
}
var expr = Expr.Parse(input, output);
if (expr == null)
{
output.WriteLine(MessageFormatter.Expected("expression"));
return null;
}
return new Let(var, expr);
}));
}
public static ExprListItem Parse(Input input, TextWriter output)
{
var str = Str.Parse(input);
if (str != null)
{
return(new ExprListItem(str));
}
var expr = Expr.Parse(input, output);
return(expr != null ? new ExprListItem(expr) : null);
}
public static Goto Parse(Input input, TextWriter output)
{
return(input.RewindOnNull(() =>
{
var cmd = input.Pop(Keyword);
if (cmd == null)
{
return null;
}
var expr = Expr.Parse(input, output);
if (expr == null)
{
output.WriteLine(MessageFormatter.Expected("expression"));
return null;
}
return new Goto(expr);
}));
}
public static Factor Parse(Input input, TextWriter output)
{
if (Dejavu(input.Index))
{
return(null);
}
indexOnPreviousVisit = input.Index;
var var = Var.Parse(input, output);
if (var != null)
{
indexOnPreviousVisit = null;
return(new Factor(var));
}
var number = Number.Parse(input);
if (number != null)
{
indexOnPreviousVisit = null;
return(new Factor(number));
}
var expr = Expr.Parse(input, output);
if (expr != null)
{
indexOnPreviousVisit = null;
return(new Factor(expr));
}
var rnd = Rnd.Parse(input, output);
if (rnd != null)
{
indexOnPreviousVisit = null;
return(new Factor(rnd));
}
return(null);
}
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);
}));
}