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package peg
import (
Possible optimizations:
1 Thanks to the `switch' optimization, for the
first item of `case' sections it is already known what the
first character is. Otherwise the case branch would not have
been entered. This patch makes use of this information and
avoids testing for the same conditions again.
l Inline leaf rules, if they contain only one element of Dot, Char,
Class or Predicate type, or such an element embedded in a
expression out of + * ? ! &.
(p) When doing a peek for Dot, Char, Class, and Predicate,
don't modify position so that it doesn't have to be restored.
r If possible, try to avoid saving and restoring of
positions. For each rule two pairs of flags will be tracked,
which tell whether the reading position, or action thunk
position might advance in case the rule matches, and in case
it does not.
s if a sequence starts with one or more `!Char'
(PeekNot for Character), insert a switch expression
Flags that are shown within braces are less effective now than they used
to be, probably because of improvements of the Go compilers.
const (
AllOptimizations = "1:l:p:r:s"
type optiFlags struct {
peek bool
elimRestore bool
inlineLeafs bool
seqPeekNot bool
unorderedFirstItem bool
func parseOptiFlags(flags string) (o *optiFlags) {
o = new(optiFlags)
if flags == "all" {
flags = AllOptimizations
for _, f := range strings.Split(flags, ":") {
if len(f) == 0 {
switch f[0] {
case '1':
o.unorderedFirstItem = true
case 'p':
o.peek = true
case 'r':
o.elimRestore = true
case 'l':
o.inlineLeafs = true
case 's':
o.seqPeekNot = true