Defaults

What the machine does when nothing says otherwise. Everything here can be changed; nothing here has to be.

The grammar’s own settings

Written in a config block — see Config Settings.

setting	default
ast-node-action	TRUE
ast-node-text	TRUE
ast-node-text-counter	TRUE
ast-node-text-series	TRUE
ast-node-char	FALSE
ast-node-char-counter	FALSE
ast-node-char-series	FALSE
scope-ordered-buffer-size	64 bytes
cache-call-buffer-size	256 slots

A grammar that writes a size of 0 has written nothing: zero is how “use the default” is stored, so it cannot also mean “none”.

The run’s own settings

Set by whoever starts the run (ApmVmConfig), not by the grammar. The runner apmr leaves all of them alone.

setting	default	what it is
variable stack	64 KiB	room for globals and every live action’s locals
stack growth	off	a grammar that wants more errors instead of growing
semvar rows	64	rows a set starts with before it doubles
call cache	the grammar’s	the run may override what the grammar asked for
call cache	on	no_cache turns it off, which is what tracing wants
trace	off	no trace is written unless a writer is given

The stack does not grow by default on purpose: a parser that wants an unbounded amount of variable space has nearly always run away, and saying so is worth more than allocating for it.

What a rule does when nothing says otherwise

	default
| and /	| takes the longest match, / takes the first
a counter	greedy, and gives nothing back
.	skips a run of the inbetween grammar, and only where it is written
an action	becomes a node named after itself
a semvar	matches its longest member; ::first takes the earliest added
a scope	one bracket, and no pairing by position