impl modulo (handle negative divisors how people expect)

src/lib/expr.test.ts

@@ -11,6 +11,11 @@ describe("expr", () => {
       ["1 * 2", "2"],
       ["1 / 2", "0.5"],
       ["1 // 2", "0"],
+      ["1 % 2", "1"],
+      ["3 % 2", "1"],
+      ["-1 % 2", "1"],
+      // TODO: might change this! negative dividend is weird no matter what, but positive modulo is arguably the better call?
+      ["1 % -2", "-1"],
       // TODO: operator precedence
       // TODO: parentheses
     ])("%s", (expression, result) => {