Add even and odd functions

src/library/mod.rs

@@ -129,6 +129,8 @@ pub fn new() -> Scope {
     std.def_func("abs", abs);
     std.def_func("min", min);
     std.def_func("max", max);
+    std.def_func("even", even);
+    std.def_func("odd", odd);
     std.def_func("range", range);
     std.def_func("rgb", rgb);
     std.def_func("lower", lower);

src/library/shape.rs

@@ -22,7 +22,7 @@ impl<S: ShapeKind> ShapeNode<S> {
     pub const STROKE: Smart<Option<Paint>> = Smart::Auto;
     /// The stroke's thickness.
     pub const THICKNESS: Length = Length::pt(1.0);
-    /// The How much to pad the shape's content.
+    /// How much to pad the shape's content.
     pub const PADDING: Linear = Linear::zero();
 
     fn construct(_: &mut EvalContext, args: &mut Args) -> TypResult<Node> {

src/library/utility.rs

@@ -135,6 +135,16 @@ pub fn max(_: &mut EvalContext, args: &mut Args) -> TypResult<Value> {
     minmax(args, Ordering::Greater)
 }
 
+/// Whether an integer is even.
+pub fn even(_: &mut EvalContext, args: &mut Args) -> TypResult<Value> {
+    Ok(Value::Bool(args.expect::<i64>("integer")? % 2 == 0))
+}
+
+/// Whether an integer is odd.
+pub fn odd(_: &mut EvalContext, args: &mut Args) -> TypResult<Value> {
+    Ok(Value::Bool(args.expect::<i64>("integer")? % 2 != 0))
+}
+
 /// Find the minimum or maximum of a sequence of values.
 fn minmax(args: &mut Args, goal: Ordering) -> TypResult<Value> {
     let mut extremum = args.expect::<Value>("value")?;

tests/typ/utility/math.typ

@@ -11,6 +11,13 @@
 #test(abs(-12pt), 12pt)
 #test(abs(50%), 50%)
 
+---
+// Test the `even` and `odd` functions.
+#test(even(2), true)
+#test(odd(2), false)
+#test(odd(-1), true)
+#test(even(-11), false)
+
 ---
 // Error: 6-16 cannot take absolute value of a linear
 #abs(10pt + 50%)