TODO

copy flag tests from mtail_test.sh

standard library, search path

refactor fs and notify into single interface

no trailing newline in parser test, requires changes to expr stmt

parse tree/ast testing?

mapping between progs and logs to reduce wasted processing

conversion in vm.compare() crashes on $var == "string" when $var is
    float (logical.mtail, input line "12.8") -- 

Using a const pattern fragment as the first or only in a pattern expr is a
    parse error.
	{"concat expr 1", `
/bar/ + X {
}`},
	{"concat expr 2", `
X {
}`},
	// 	{"match expression 3", `
	// $foo =~ X {
	// }
	// `},

Match against a variable requires simplifying binaryExpr grammar to elim the
    concat_expr branch, fixing the id_expr problem above
	{"match expr 2", `
/(?P<foo>.{6}) (?P<bar>.*)/ {
  $foo =~ $bar {
  }
}`},


bytecode like
[{push 1} {push 0} {cmp 1} {jm 6} {push 0} {jmp 7} {push 1} {jnm 13}
    {setmatched false} {mload 0} {dload 0} {inc <nil>} {setmatched true}]
can be expressed as
[{push 1} {push 0} {cmp 1} {jm 9} {setmatched false} {mload 0} {dload 0} {inc
    <nil>} {setmatched true}]
but jnm 13 is from the condExpr and the previous is from a comparison binary
    expr; an optimizer is needed to collapse the bytecode to undersand that
    cmp, jm, push, jump, push, jnm in sequence like so is the same as a cmp, jm
and we need to worry about the jump table too


count stack size and preallocate stack
-> counts of push/pop per instruction
-> test to keep p/p counts updated


Run and upload benchmarks to https://perfdata.golang.org/ from circleci


# Won't do

X Use capture group references to feed back to declaring regular expression,
X     noting unused caprefs,
X     possibly flipping back to noncapturing (and renumbering the caprefs?)
X -> unlikely to implement, probably won't impact regexp speed