tweak fn parsing

src/internal/parser.ts

@@ -450,7 +450,7 @@ export const language = P.createLanguage({
 			P.regexp(/[a-z0-9_]+/i),
 			P.seq([
 				P.str('='),
-				P.regexp(/[a-z0-9_.]+/i),
+				P.regexp(/[a-z0-9_.-]+/i),
 			], 1).option(),
 		]).map(result => {
 			return {

test/parser.ts

@@ -1199,6 +1199,16 @@ hoge`;
 			assert.deepStrictEqual(mfm.parse(input), output);
 		});
 
+		it('with a string argument 2', () => {
+			const input = '$[position.x=-3 a]';
+			const output = [
+				FN('position', { x: '-3' }, [
+					TEXT('a')
+				])
+			];
+			assert.deepStrictEqual(mfm.parse(input), output);
+		});
+
 		it('invalid fn name', () => {
 			const input = '$[関数 text]';
 			const output = [