Support tokenizing `.` wildcard operator.

* src/paca.mjs
  (isTransition): Add new function as an improved version of the raw
    usage of `stateTransitionOperators`, equivalent to `isAnchor()` and
    `isOperator()`.
  (operatorChars, isOperator): Add new static set `operatorChars` as
    backing data of `isOperator()`, instead of ad-hoc conditional in its
    implementation.  Also now add the `.` character as an operator by
    including it in the `operatorChars` set.
  (tokenizeRegexStep): Use the new `isTransition()` function instead of
    checking the set directly.  Also tweak ternary to fit in 80 columns.
  (PRECEDENCE): Add `.` operator with lowest precedence, as it is not
    really operating on anything, and is instead a target to be operated
    on.
* tests/paca.mjs
  (test_isTransition): Add obligatory test cases.
  (test_isOperator): Include test case for `.` wildcard operator.

1 files changed, 10 insertions, 5 deletions

diff --git a/src/paca.mjs b/src/paca.mjs
index 42c2f88..5d11b05 100644
--- a/src/paca.mjs
+++ b/src/paca.mjs
@@ -306,14 +306,16 @@ const ANCHOR_FNS = {
 };
 
 const anchors = new Set(Object.keys(ANCHOR_FNS));
-
 const isAnchor = char =>
 	anchors.has(char);
 
-const stateTransitionOperators = new Set(Object.keys(TRANSITION_FNS));
+const transitionChars = new Set(Object.keys(TRANSITION_FNS));
+const isTransition = char =>
+	transitionChars.has(char);
 
+const operatorChars = new Set([...nonConcatOperators, "(", "."]);
 const isOperator = char =>
-	nonConcatOperators.has(char) || char == "(";
+	operatorChars.has(char);
 
 const tokenizeRegexStep = chars => ({ out, state, context }, char, index) => {
 	const next = chars[index + 1];
@@ -327,7 +329,7 @@ const tokenizeRegexStep = chars => ({ out, state, context }, char, index) => {
 		);
 	}
 
-	if (stateTransitionOperators.has(char)) {
+	if (isTransition(char)) {
 		return TRANSITION_FNS[char](
 			{ out, state, context },
 			char,
@@ -349,7 +351,9 @@ const tokenizeRegexStep = chars => ({ out, state, context }, char, index) => {
 	return {
 		out: out.concat(
 			op,
-			shouldConcat(char, next) ? [{ operator: "concat" }] : [],
+			shouldConcat(char, next)
+				? [{ operator: "concat" }]
+				: [],
 		),
 		state,
 		context,
@@ -385,6 +389,7 @@ const PRECEDENCE = {
 	"concat": 2,
 	"|":      1,
 	"class":  1,
+	".":      1,
 };
 
 const shouldPush = (stack, token) =>