diff --git a/src/lib/expr.test.ts b/src/lib/expr.test.ts
index 3ed361f..fbb0edb 100644
--- a/src/lib/expr.test.ts
+++ b/src/lib/expr.test.ts
@@ -10,12 +10,24 @@ describe("expr", () => {
       ["1 - 2", "-1"],
       ["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"],
+      // floored division
+      ["1 // 5", "0"],
+      ["6 // 5", "1"],
+      ["-1 // 5", "-1"],
+      ["-6 // 5", "-2"],
+      ["1 // -5", "-1"],
+      ["6 // -5", "-2"],
+      ["-1 // -5", "0"],
+      ["-6 // -5", "1"],
+      // floored modulo
+      ["1 % 5", "1"],
+      ["6 % 5", "1"],
+      ["-6 % 5", "4"],
+      ["-1 % 5", "4"],
+      ["1 % -5", "-4"],
+      ["6 % -5", "-4"],
+      ["-6 % -5", "-1"],
+      ["-1 % -5", "-1"],
       // TODO: operator precedence
       // TODO: parentheses
     ])("%s", (expression, result) => {
diff --git a/src/lib/expr.ts b/src/lib/expr.ts
index 9d6afb2..81df33e 100644
--- a/src/lib/expr.ts
+++ b/src/lib/expr.ts
@@ -12,8 +12,8 @@ export function Expr({}, argv: TextPiece[]): ProcResult {
   const parser = new ExpressionParser(expression);
   const result = parser.parseSubExpression(0);
 
-  if(parser.pos != expression.length) {
-    return {error: "Couldn't parse full expression"}
+  if (parser.pos != expression.length) {
+    return { error: "Couldn't parse full expression" };
   }
 
   if ("value" in result) {
@@ -59,13 +59,20 @@ function map(
   }
 }
 
-function makeInfixOp(token:RegExp, leftBindingPower: number,rightBindingPower: number, op: (left: number, right: number) => Value | ErrorResult):TokenHandler {
+function makeInfixOp(
+  token: RegExp,
+  leftBindingPower: number,
+  rightBindingPower: number,
+  op: (left: number, right: number) => Value | ErrorResult
+): TokenHandler {
   return {
     leftBindingPower,
     token,
     parse: ({ value: left }, matched, parser) =>
-      map(parser.parseSubExpression(rightBindingPower), (right) => op(left, right)),
-  }
+      map(parser.parseSubExpression(rightBindingPower), (right) =>
+        op(left, right)
+      ),
+  };
 }
 
 const Operators: TokenHandler[] = [
@@ -78,14 +85,18 @@ const Operators: TokenHandler[] = [
     leftBindingPower: -1,
     token: MINUS_TOKEN,
     parse: (left, matched, parser) =>
-      map(parser.parseSubExpression(99), (right) => ({value: -right})),
+      map(parser.parseSubExpression(99), (right) => ({ value: -right })),
   },
   makeInfixOp(PLUS_TOKEN, 10, 11, (left, right) => ({ value: left + right })),
   makeInfixOp(MINUS_TOKEN, 10, 11, (left, right) => ({ value: left - right })),
   makeInfixOp(TIMES_TOKEN, 20, 21, (left, right) => ({ value: left * right })),
-  makeInfixOp(FLOOR_TOKEN, 20, 21, (left, right) => ({ value: Math.floor(left / right) })),
+  makeInfixOp(FLOOR_TOKEN, 20, 21, (left, right) => ({
+    value: Math.floor(left / right),
+  })),
   makeInfixOp(DIV_TOKEN, 20, 21, (left, right) => ({ value: left / right })),
-  makeInfixOp(MOD_TOKEN, 20, 21, (left, right) => ({ value: ((left % right) + right) % right })),
+  makeInfixOp(MOD_TOKEN, 20, 21, (left, right) => ({
+    value: ((left % right) + right) % right,
+  })),
 ];
 
 const ZERO = { value: 0 };