Cobra Inline Programming Language Begin and End

NAME

Begin and End — first and last token in input sequence

SYNTAX

	Begin
	End
	first_t
	last_t

DESCRIPTION

Begin is a token reference that points to the first lexical token in the part of the input sequence that was assigned to the current cpu. Similarly, End points to the last lexical token in that sequence.

If executing single-core these are also the first and last tokens in the entire input stream. In multi-core mode, though, the part of the input sequence assigned to each cpu-core will be different. In that case the identifiers first_t and last_t can be used to refer to the first and last token in the entire input sequence, not just the part assigned to the current cpu-core.

In single-core mode Begin and first_t point to the same token, as do End and last_t.

EXAMPLES

	%{
		. = Begin;
		while (true)
		{	print .txt "\n";
			if (. == last_t)
			{	break;
			}
			. = .nxt;
		}
		Stop;
	%}
There are a few different ways to traverse the token sequence. The default is to let Cobra do the scan and execute the inline program once for each token in the sequence. For instance, to count the number of identifiers: 
	%{
		if (@ident)
		{	cnt++;
		}
	%}
	%{
		print "there are " cnt " identifiers\n";
		Stop;	# print result once, and stop
	%}
Equivalently, when taking over the scan itself: 
	%{
		while (.seq <= End.seq)		# or while (. != End)
		{	if (@ident)
			{	cnt++;
			}
			. = .nxt;		# move to next token
		}
		print "there are " cnt " identifiers\n";
		Stop;				# done with all tokens
	%}
Similarly it is easy to traverse the sequence backwards, or in any other order, using the token attributes .prv, .nxt, or .jmp (to jump over token sequences enclosed in round, square, or curly braces).

SEE ALSO

core, ncore, tokens.
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Tutorial 		(Last Updated: 26 July 2023)