public static LoopHeader Loop(MatchIterator iterator)
{
Expression array;
iterator.AssertKeyword(Keywords.Loop);
Token loop = (Token)iterator.Current;
if (iterator.AtEnd())
{
LoopHeader result = new LoopHeader(loop);
return(result);
}
iterator.AssertExpression(out Expression firstExpression);
if (iterator.AtEnd())
{
// Actually checking that this expression is an array is for
// a later step, when the messenger is available.
array = firstExpression;
LoopHeader result = new LoopHeader(loop, array);
return(result);
}
if (iterator.NextIsKeyword(Keywords.In, out Token inToken))
{
// Again, actually checking that this is indeed just a name
// has to wait for a later stage.
Expression name = firstExpression;
iterator.AssertExpression(out array);
iterator.AssertEnd();
LoopHeader result = new LoopHeader(loop, name, inToken, array);
return(result);
}
if (iterator.NextIsKeyword(Keywords.From, out Token from))
{
Expression name = firstExpression;
iterator.AssertExpression(out Expression start);
iterator.AssertKeyword(Keywords.To, out Token to);
iterator.AssertExpression(out Expression end);
iterator.AssertEnd();
LoopHeader result = new LoopHeader(
loop, name, from, start, to, end);
return(result);
}
throw iterator.UnexpectedEnd();
}