Make `Relative` generic

34 files changed, 305 insertions, 281 deletions

diff --git a/src/eval/layout.rs b/src/eval/layout.rs
index f541694c..9bf44194 100644
--- a/src/eval/layout.rs
+++ b/src/eval/layout.rs
@@ -8,7 +8,9 @@ use std::sync::Arc;
 use super::{Barrier, StyleChain};
 use crate::diag::TypResult;
 use crate::frame::{Element, Frame, Geometry, Shape, Stroke};
-use crate::geom::{Align, Length, Paint, Point, Relative, Sides, Size, Spec, Transform};
+use crate::geom::{
+    Align, Length, Numeric, Paint, Point, Relative, Sides, Size, Spec, Transform,
+};
 use crate::library::graphics::MoveNode;
 use crate::library::layout::{AlignNode, PadNode};
 use crate::util::Prehashed;
@@ -161,7 +163,7 @@ impl LayoutNode {
     }
 
     /// Force a size for this node.
-    pub fn sized(self, sizing: Spec<Option<Relative>>) -> Self {
+    pub fn sized(self, sizing: Spec<Option<Relative<Length>>>) -> Self {
         if sizing.any(Option::is_some) {
             SizedNode { sizing, child: self }.pack()
         } else {
@@ -189,7 +191,7 @@ impl LayoutNode {
     }
 
     /// Pad this node at the sides.
-    pub fn padded(self, padding: Sides<Relative>) -> Self {
+    pub fn padded(self, padding: Sides<Relative<Length>>) -> Self {
         if !padding.left.is_zero()
             || !padding.top.is_zero()
             || !padding.right.is_zero()
@@ -205,7 +207,7 @@ impl LayoutNode {
     pub fn moved(self, offset: Point) -> Self {
         if !offset.is_zero() {
             MoveNode {
-                transform: Transform::translation(offset.x, offset.y),
+                transform: Transform::translate(offset.x, offset.y),
                 child: self,
             }
             .pack()
@@ -292,7 +294,7 @@ impl Layout for EmptyNode {
 #[derive(Debug, Hash)]
 struct SizedNode {
     /// How to size the node horizontally and vertically.
-    sizing: Spec<Option<Relative>>,
+    sizing: Spec<Option<Relative<Length>>>,
     /// The node to be sized.
     child: LayoutNode,
 }
diff --git a/src/eval/ops.rs b/src/eval/ops.rs
index 024de433..ff21d93f 100644
--- a/src/eval/ops.rs
+++ b/src/eval/ops.rs
@@ -2,7 +2,7 @@ use std::cmp::Ordering;
 
 use super::{Dynamic, StrExt, Value};
 use crate::diag::StrResult;
-use crate::geom::{Align, Spec, SpecAxis};
+use crate::geom::{Align, Numeric, Spec, SpecAxis};
 use Value::*;
 
 /// Bail with a type mismatch error.
@@ -66,12 +66,12 @@ pub fn add(lhs: Value, rhs: Value) -> StrResult<Value> {
         (Angle(a), Angle(b)) => Angle(a + b),
 
         (Length(a), Length(b)) => Length(a + b),
-        (Length(a), Ratio(b)) => Relative(a + b),
-        (Length(a), Relative(b)) => Relative(a + b),
+        (Length(a), Ratio(b)) => Relative(b + a),
+        (Length(a), Relative(b)) => Relative(b + a),
 
         (Ratio(a), Length(b)) => Relative(a + b),
         (Ratio(a), Ratio(b)) => Ratio(a + b),
-        (Ratio(a), Relative(b)) => Relative(a + b),
+        (Ratio(a), Relative(b)) => Relative(b + a),
 
         (Relative(a), Length(b)) => Relative(a + b),
         (Relative(a), Ratio(b)) => Relative(a + b),
@@ -123,15 +123,15 @@ pub fn sub(lhs: Value, rhs: Value) -> StrResult<Value> {
         (Angle(a), Angle(b)) => Angle(a - b),
 
         (Length(a), Length(b)) => Length(a - b),
-        (Length(a), Ratio(b)) => Relative(a - b),
-        (Length(a), Relative(b)) => Relative(a - b),
+        (Length(a), Ratio(b)) => Relative(-b + a),
+        (Length(a), Relative(b)) => Relative(-b + a),
 
-        (Ratio(a), Length(b)) => Relative(a - b),
+        (Ratio(a), Length(b)) => Relative(a + -b),
         (Ratio(a), Ratio(b)) => Ratio(a - b),
-        (Ratio(a), Relative(b)) => Relative(a - b),
+        (Ratio(a), Relative(b)) => Relative(-b + a),
 
-        (Relative(a), Length(b)) => Relative(a - b),
-        (Relative(a), Ratio(b)) => Relative(a - b),
+        (Relative(a), Length(b)) => Relative(a + -b),
+        (Relative(a), Ratio(b)) => Relative(a + -b),
         (Relative(a), Relative(b)) => Relative(a - b),
 
         (Fraction(a), Fraction(b)) => Fraction(a - b),
diff --git a/src/eval/value.rs b/src/eval/value.rs
index 774ae0b6..44df89e2 100644
--- a/src/eval/value.rs
+++ b/src/eval/value.rs
@@ -31,7 +31,7 @@ pub enum Value {
     /// A ratio: `50%`.
     Ratio(Ratio),
     /// A relative length, combination of a ratio and a length: `20% + 5cm`.
-    Relative(Relative),
+    Relative(Relative<Length>),
     /// A fraction: `1fr`.
     Fraction(Fraction),
     /// A color value: `#f79143ff`.
@@ -549,7 +549,7 @@ primitive! { f64: "float", Float, Int(v) => v as f64 }
 primitive! { Length: "length", Length }
 primitive! { Angle: "angle", Angle }
 primitive! { Ratio: "ratio", Ratio }
-primitive! { Relative: "relative length", Relative, Length(v) => v.into(), Ratio(v) => v.into() }
+primitive! { Relative<Length>: "relative length", Relative, Length(v) => v.into(), Ratio(v) => v.into() }
 primitive! { Fraction: "fraction", Fraction }
 primitive! { Color: "color", Color }
 primitive! { EcoString: "string", Str }
diff --git a/src/export/pdf.rs b/src/export/pdf.rs
index 2550519b..95d20c51 100644
--- a/src/export/pdf.rs
+++ b/src/export/pdf.rs
@@ -17,7 +17,7 @@ use ttf_parser::{name_id, GlyphId, Tag};
 use super::subset::subset;
 use crate::font::{find_name, FaceId, FontStore};
 use crate::frame::{Element, Frame, Geometry, Group, Shape, Stroke, Text};
-use crate::geom::{self, Color, Em, Length, Paint, Point, Size, Transform};
+use crate::geom::{self, Color, Em, Length, Numeric, Paint, Point, Size, Transform};
 use crate::image::{Image, ImageId, ImageStore, RasterImage};
 use crate::Context;
 
@@ -423,7 +423,7 @@ impl<'a> PageExporter<'a> {
     }
 
     fn write_group(&mut self, pos: Point, group: &Group) {
-        let translation = Transform::translation(pos.x, pos.y);
+        let translation = Transform::translate(pos.x, pos.y);
 
         self.save_state();
         self.transform(translation.pre_concat(group.transform));
diff --git a/src/font.rs b/src/font.rs
index 46d6b8d7..e1d0c4e6 100644
--- a/src/font.rs
+++ b/src/font.rs
@@ -415,7 +415,7 @@ pub enum VerticalFontMetric {
     Descender,
     /// An font-size dependent distance from the baseline (positive goes up, negative
     /// down).
-    Relative(Relative),
+    Relative(Relative<Length>),
 }
 
 /// Properties of a single font face.
diff --git a/src/frame.rs b/src/frame.rs
index 7cc564cc..3c747f0d 100644
--- a/src/frame.rs
+++ b/src/frame.rs
@@ -4,7 +4,9 @@ use std::fmt::{self, Debug, Formatter};
 use std::sync::Arc;
 
 use crate::font::FaceId;
-use crate::geom::{Align, Em, Length, Paint, Path, Point, Size, Spec, Transform};
+use crate::geom::{
+    Align, Em, Length, Numeric, Paint, Path, Point, Size, Spec, Transform,
+};
 use crate::image::ImageId;
 
 /// A finished layout with elements at fixed positions.
diff --git a/src/geom/angle.rs b/src/geom/angle.rs
index b64ec77e..a0900ce5 100644
--- a/src/geom/angle.rs
+++ b/src/geom/angle.rs
@@ -10,6 +10,16 @@ impl Angle {
         Self(Scalar(0.0))
     }
 
+    /// Create an angle from a number of raw units.
+    pub const fn raw(raw: f64) -> Self {
+        Self(Scalar(raw))
+    }
+
+    /// Create an angle from a value in a unit.
+    pub fn with_unit(val: f64, unit: AngularUnit) -> Self {
+        Self(Scalar(val * unit.raw_scale()))
+    }
+
     /// Create an angle from a number of radians.
     pub fn rad(rad: f64) -> Self {
         Self::with_unit(rad, AngularUnit::Rad)
@@ -20,9 +30,14 @@ impl Angle {
         Self::with_unit(deg, AngularUnit::Deg)
     }
 
-    /// Create an angle from a number of raw units.
-    pub const fn raw(raw: f64) -> Self {
-        Self(Scalar(raw))
+    /// Get the value of this angle in raw units.
+    pub const fn to_raw(self) -> f64 {
+        (self.0).0
+    }
+
+    /// Get the value of this length in unit.
+    pub fn to_unit(self, unit: AngularUnit) -> f64 {
+        self.to_raw() / unit.raw_scale()
     }
 
     /// Convert this to a number of radians.
@@ -35,9 +50,9 @@ impl Angle {
         self.to_unit(AngularUnit::Deg)
     }
 
-    /// Get the value of this angle in raw units.
-    pub const fn to_raw(self) -> f64 {
-        (self.0).0
+    /// The absolute value of the this angle.
+    pub fn abs(self) -> Self {
+        Self::raw(self.to_raw().abs())
     }
 
     /// Get the sine of this angle in radians.
@@ -49,20 +64,15 @@ impl Angle {
     pub fn cos(self) -> f64 {
         self.to_rad().cos()
     }
+}
 
-    /// Create an angle from a value in a unit.
-    pub fn with_unit(val: f64, unit: AngularUnit) -> Self {
-        Self(Scalar(val * unit.raw_scale()))
-    }
-
-    /// Get the value of this length in unit.
-    pub fn to_unit(self, unit: AngularUnit) -> f64 {
-        self.to_raw() / unit.raw_scale()
+impl Numeric for Angle {
+    fn zero() -> Self {
+        Self::zero()
     }
 
-    /// The absolute value of the this angle.
-    pub fn abs(self) -> Self {
-        Self::raw(self.to_raw().abs())
+    fn is_finite(self) -> bool {
+        self.0.is_finite()
     }
 }
 
@@ -132,6 +142,7 @@ impl Sum for Angle {
         Self(iter.map(|s| s.0).sum())
     }
 }
+
 /// Different units of angular measurement.
 #[derive(Copy, Clone, Eq, PartialEq, Hash)]
 pub enum AngularUnit {
diff --git a/src/geom/em.rs b/src/geom/em.rs
index d1e90e04..3c772d96 100644
--- a/src/geom/em.rs
+++ b/src/geom/em.rs
@@ -32,19 +32,24 @@ impl Em {
         Self(Scalar(length / font_size))
     }
 
+    /// The number of em units.
+    pub const fn get(self) -> f64 {
+        (self.0).0
+    }
+
     /// Convert to a length at the given font size.
     pub fn resolve(self, font_size: Length) -> Length {
         self.get() * font_size
     }
+}
 
-    /// The number of em units.
-    pub const fn get(self) -> f64 {
-        (self.0).0
+impl Numeric for Em {
+    fn zero() -> Self {
+        Self::zero()
     }
 
-    /// Whether the length is zero.
-    pub fn is_zero(self) -> bool {
-        self.0 == 0.0
+    fn is_finite(self) -> bool {
+        self.0.is_finite()
     }
 }
 
diff --git a/src/geom/fraction.rs b/src/geom/fraction.rs
index 7da85779..2f33a134 100644
--- a/src/geom/fraction.rs
+++ b/src/geom/fraction.rs
@@ -25,11 +25,6 @@ impl Fraction {
         (self.0).0
     }
 
-    /// Whether the fraction is zero.
-    pub fn is_zero(self) -> bool {
-        self.0 == 0.0
-    }
-
     /// The absolute value of the this fraction.
     pub fn abs(self) -> Self {
         Self::new(self.get().abs())
@@ -46,6 +41,16 @@ impl Fraction {
     }
 }
 
+impl Numeric for Fraction {
+    fn zero() -> Self {
+        Self::zero()
+    }
+
+    fn is_finite(self) -> bool {
+        self.0.is_finite()
+    }
+}
+
 impl Debug for Fraction {
     fn fmt(&self, f: &mut Formatter) -> fmt::Result {
         write!(f, "{}fr", round_2(self.get()))
diff --git a/src/geom/length.rs b/src/geom/length.rs
index c5fbfd76..838d33c0 100644
--- a/src/geom/length.rs
+++ b/src/geom/length.rs
@@ -15,6 +15,16 @@ impl Length {
         Self(Scalar(f64::INFINITY))
     }
 
+    /// Create a length from a number of raw units.
+    pub const fn raw(raw: f64) -> Self {
+        Self(Scalar(raw))
+    }
+
+    /// Create a length from a value in a unit.
+    pub fn with_unit(val: f64, unit: LengthUnit) -> Self {
+        Self(Scalar(val * unit.raw_scale()))
+    }
+
     /// Create a length from a number of points.
     pub fn pt(pt: f64) -> Self {
         Self::with_unit(pt, LengthUnit::Pt)
@@ -35,9 +45,14 @@ impl Length {
         Self::with_unit(inches, LengthUnit::In)
     }
 
-    /// Create a length from a number of raw units.
-    pub const fn raw(raw: f64) -> Self {
-        Self(Scalar(raw))
+    /// Get the value of this length in raw units.
+    pub const fn to_raw(self) -> f64 {
+        (self.0).0
+    }
+
+    /// Get the value of this length in unit.
+    pub fn to_unit(self, unit: LengthUnit) -> f64 {
+        self.to_raw() / unit.raw_scale()
     }
 
     /// Convert this to a number of points.
@@ -60,36 +75,6 @@ impl Length {
         self.to_unit(LengthUnit::In)
     }
 
-    /// Get the value of this length in raw units.
-    pub const fn to_raw(self) -> f64 {
-        (self.0).0
-    }
-
-    /// Create a length from a value in a unit.
-    pub fn with_unit(val: f64, unit: LengthUnit) -> Self {
-        Self(Scalar(val * unit.raw_scale()))
-    }
-
-    /// Get the value of this length in unit.
-    pub fn to_unit(self, unit: LengthUnit) -> f64 {
-        self.to_raw() / unit.raw_scale()
-    }
-
-    /// Whether the length is zero.
-    pub fn is_zero(self) -> bool {
-        self.to_raw() == 0.0
-    }
-
-    /// Whether the length is finite.
-    pub fn is_finite(self) -> bool {
-        self.to_raw().is_finite()
-    }
-
-    /// Whether the length is infinite.
-    pub fn is_infinite(self) -> bool {
-        self.to_raw().is_infinite()
-    }
-
     /// The absolute value of the this length.
     pub fn abs(self) -> Self {
         Self::raw(self.to_raw().abs())
@@ -137,6 +122,16 @@ impl Length {
     }
 }
 
+impl Numeric for Length {
+    fn zero() -> Self {
+        Self::zero()
+    }
+
+    fn is_finite(self) -> bool {
+        self.0.is_finite()
+    }
+}
+
 impl Debug for Length {
     fn fmt(&self, f: &mut Formatter) -> fmt::Result {
         write!(f, "{}pt", round_2(self.to_pt()))
diff --git a/src/geom/mod.rs b/src/geom/mod.rs
index 8d7759b4..bfb450a1 100644
--- a/src/geom/mod.rs
+++ b/src/geom/mod.rs
@@ -60,6 +60,30 @@ pub trait Get<Index> {
     }
 }
 
+/// A numeric type.
+pub trait Numeric:
+    Sized
+    + Debug
+    + Copy
+    + PartialEq
+    + Neg<Output = Self>
+    + Add<Output = Self>
+    + Sub<Output = Self>
+    + Mul<f64, Output = Self>
+    + Div<f64, Output = Self>
+{
+    /// The identity element.
+    fn zero() -> Self;
+
+    /// Whether `self` is the identity element.
+    fn is_zero(self) -> bool {
+        self == Self::zero()
+    }
+
+    /// Whether `self` contains only finite parts.
+    fn is_finite(self) -> bool;
+}
+
 /// Round a float to two decimal places.
 fn round_2(value: f64) -> f64 {
     (value * 100.0).round() / 100.0
diff --git a/src/geom/paint.rs b/src/geom/paint.rs
index 8dee363c..3660d528 100644
--- a/src/geom/paint.rs
+++ b/src/geom/paint.rs
@@ -1,4 +1,3 @@
-use std::fmt::Display;
 use std::str::FromStr;
 
 use syntect::highlighting::Color as SynColor;
@@ -103,7 +102,7 @@ impl RgbaColor {
 }
 
 impl FromStr for RgbaColor {
-    type Err = RgbaError;
+    type Err = &'static str;
 
     /// Constructs a new color from hex strings like the following:
     /// - `#aef` (shorthand, with leading hashtag),
@@ -113,8 +112,8 @@ impl FromStr for RgbaColor {
     /// The hashtag is optional and both lower and upper case are fine.
     fn from_str(hex_str: &str) -> Result<Self, Self::Err> {
         let hex_str = hex_str.strip_prefix('#').unwrap_or(hex_str);
-        if !hex_str.is_ascii() {
-            return Err(RgbaError);
+        if hex_str.chars().any(|c| !c.is_ascii_hexdigit()) {
+            return Err("string contains non-hexadecimal letters");
         }
 
         let len = hex_str.len();
@@ -123,7 +122,7 @@ impl FromStr for RgbaColor {
         let alpha = len == 4 || len == 8;
 
         if !long && !short {
-            return Err(RgbaError);
+            return Err("string has wrong length");
         }
 
         let mut values: [u8; 4] = [255; 4];
@@ -133,7 +132,7 @@ impl FromStr for RgbaColor {
             let pos = elem * item_len;
 
             let item = &hex_str[pos .. (pos + item_len)];
-            values[elem] = u8::from_str_radix(item, 16).map_err(|_| RgbaError)?;
+            values[elem] = u8::from_str_radix(item, 16).unwrap();
 
             if short {
                 // Duplicate number for shorthand notation, i.e. `a` -> `aa`
@@ -169,18 +168,6 @@ impl Debug for RgbaColor {
     }
 }
 
-/// The error when parsing an [`RgbaColor`] from a string fails.
-#[derive(Debug, Copy, Clone, Eq, PartialEq)]
-pub struct RgbaError;
-
-impl Display for RgbaError {
-    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-        f.pad("invalid hex string")
-    }
-}
-
-impl std::error::Error for RgbaError {}
-
 /// An 8-bit CMYK color.
 #[derive(Copy, Clone, Eq, PartialEq, Hash)]
 pub struct CmykColor {
@@ -268,13 +255,14 @@ mod tests {
     #[test]
     fn test_parse_invalid_colors() {
         #[track_caller]
-        fn test(hex: &str) {
-            assert_eq!(RgbaColor::from_str(hex), Err(RgbaError));
+        fn test(hex: &str, message: &str) {
+            assert_eq!(RgbaColor::from_str(hex), Err(message));
         }
 
-        test("12345");
-        test("a5");
-        test("14B2AH");
-        test("f075ff011");
+        test("a5", "string has wrong length");
+        test("12345", "string has wrong length");
+        test("f075ff011", "string has wrong length");
+        test("hmmm", "string contains non-hexadecimal letters");
+        test("14B2AH", "string contains non-hexadecimal letters");
     }
 }
diff --git a/src/geom/point.rs b/src/geom/point.rs
index 6d77507b..afce68ba 100644
--- a/src/geom/point.rs
+++ b/src/geom/point.rs
@@ -35,20 +35,25 @@ impl Point {
         Self { x: Length::zero(), y }
     }
 
-    /// Whether both components are zero.
-    pub fn is_zero(self) -> bool {
-        self.x.is_zero() && self.y.is_zero()
-    }
-
     /// Transform the point with the given transformation.
-    pub fn transform(self, transform: Transform) -> Self {
+    pub fn transform(self, ts: Transform) -> Self {
         Self::new(
-            transform.sx.resolve(self.x) + transform.kx.resolve(self.y) + transform.tx,
-            transform.ky.resolve(self.x) + transform.sy.resolve(self.y) + transform.ty,
+            ts.sx.resolve(self.x) + ts.kx.resolve(self.y) + ts.tx,
+            ts.ky.resolve(self.x) + ts.sy.resolve(self.y) + ts.ty,
         )
     }
 }
 
+impl Numeric for Point {
+    fn zero() -> Self {
+        Self::zero()
+    }
+
+    fn is_finite(self) -> bool {
+        self.x.is_finite() && self.y.is_finite()
+    }
+}
+
 impl Get<SpecAxis> for Point {
     type Component = Length;
 
diff --git a/src/geom/ratio.rs b/src/geom/ratio.rs
index d035c33e..7dca53c2 100644
--- a/src/geom/ratio.rs
+++ b/src/geom/ratio.rs
@@ -28,16 +28,6 @@ impl Ratio {
         (self.0).0
     }
 
-    /// Resolve this relative to the given `length`.
-    pub fn resolve(self, length: Length) -> Length {
-        // We don't want NaNs.
-        if length.is_infinite() {
-            Length::zero()
-        } else {
-            self.get() * length
-        }
-    }
-
     /// Whether the ratio is zero.
     pub fn is_zero(self) -> bool {
         self.0 == 0.0
@@ -52,6 +42,12 @@ impl Ratio {
     pub fn abs(self) -> Self {
         Self::new(self.get().abs())
     }
+
+    /// Resolve this relative to the given `whole`.
+    pub fn resolve<T: Numeric>(self, whole: T) -> T {
+        let resolved = whole * self.get();
+        if resolved.is_finite() { resolved } else { T::zero() }
+    }
 }
 
 impl Debug for Ratio {
diff --git a/src/geom/relative.rs b/src/geom/relative.rs
index fa2ec7fc..8e8897e7 100644
--- a/src/geom/relative.rs
+++ b/src/geom/relative.rs
@@ -1,65 +1,60 @@
 use super::*;
 
-/// A relative length.
+/// A value that is composed of a relative and an absolute part.
 #[derive(Default, Copy, Clone, Eq, PartialEq, Hash)]
-pub struct Relative {
+pub struct Relative<T: Numeric> {
     /// The relative part.
     pub rel: Ratio,
     /// The absolute part.
-    pub abs: Length,
+    pub abs: T,
 }
 
-impl Relative {
-    /// The zero relative length.
-    pub const fn zero() -> Self {
-        Self { rel: Ratio::zero(), abs: Length::zero() }
+impl<T: Numeric> Relative<T> {
+    /// The zero relative.
+    pub fn zero() -> Self {
+        Self { rel: Ratio::zero(), abs: T::zero() }
     }
 
-    /// A relative length with a ratio of `100%` and no absolute part.
-    pub const fn one() -> Self {
-        Self { rel: Ratio::one(), abs: Length::zero() }
+    /// A relative with a ratio of `100%` and no absolute part.
+    pub fn one() -> Self {
+        Self { rel: Ratio::one(), abs: T::zero() }
     }
 
-    /// Create a new relative length from its parts.
-    pub const fn new(rel: Ratio, abs: Length) -> Self {
+    /// Create a new relative from its parts.
+    pub fn new(rel: Ratio, abs: T) -> Self {
         Self { rel, abs }
     }
 
-    /// Resolve this length relative to the given `length`.
-    pub fn resolve(self, length: Length) -> Length {
-        self.rel.resolve(length) + self.abs
-    }
-
     /// Whether both parts are zero.
     pub fn is_zero(self) -> bool {
         self.rel.is_zero() && self.abs.is_zero()
     }
 
-    /// Whether there is a relative part.
-    pub fn is_relative(self) -> bool {
-        !self.rel.is_zero()
+    /// Resolve this relative to the given `whole`.
+    pub fn resolve(self, whole: T) -> T {
+        self.rel.resolve(whole) + self.abs
     }
 }
 
-impl Debug for Relative {
+impl<T: Numeric> Debug for Relative<T> {
     fn fmt(&self, f: &mut Formatter) -> fmt::Result {
         write!(f, "{:?} + {:?}", self.rel, self.abs)
     }
 }
 
-impl From<Length> for Relative {
-    fn from(abs: Length) -> Self {
+impl<T: Numeric> From<T> for Relative<T> {
+    fn from(abs: T) -> Self {
         Self { rel: Ratio::zero(), abs }
     }
 }
 
-impl From<Ratio> for Relative {
+impl<T: Numeric> From<Ratio> for Relative<T> {
     fn from(rel: Ratio) -> Self {
-        Self { rel, abs: Length::zero() }
+        Self { rel, abs: T::zero() }
     }
 }
 
-impl Neg for Relative {
+impl<T: Numeric> Neg for Relative<T> {
     type Output = Self;
 
     fn neg(self) -> Self {
@@ -67,10 +62,10 @@ impl Neg for Relative {
     }
 }
 
-impl Add for Relative {
+impl<T: Numeric> Add for Relative<T> {
     type Output = Self;
 
-    fn add(self, other: Self) -> Self {
+    fn add(self, other: Self) -> Self::Output {
         Self {
             rel: self.rel + other.rel,
             abs: self.abs + other.abs,
@@ -78,97 +73,88 @@ impl Add for Relative {
     }
 }
 
-impl Add<Ratio> for Length {
-    type Output = Relative;
+impl<T: Numeric> Sub for Relative<T> {
+    type Output = Self;
 
-    fn add(self, other: Ratio) -> Relative {
-        Relative { rel: other, abs: self }
+    fn sub(self, other: Self) -> Self::Output {
+        self + -other
     }
 }
 
-impl Add<Length> for Ratio {
-    type Output = Relative;
+impl<T: Numeric> Mul<f64> for Relative<T> {
+    type Output = Self;
 
-    fn add(self, other: Length) -> Relative {
-        other + self
+    fn mul(self, other: f64) -> Self::Output {
+        Self {
+            rel: self.rel * other,
+            abs: self.abs * other,
+        }
     }
 }
 
-impl Add<Length> for Relative {
-    type Output = Self;
+impl<T: Numeric> Mul<Relative<T>> for f64 {
+    type Output = Relative<T>;
 
-    fn add(self, other: Length) -> Self {
-        Self { rel: self.rel, abs: self.abs + other }
+    fn mul(self, other: Relative<T>) -> Self::Output {
+        other * self
     }
 }
 
-impl Add<Relative> for Length {
-    type Output = Relative;
+impl<T: Numeric> Div<f64> for Relative<T> {
+    type Output = Self;
 
-    fn add(self, other: Relative) -> Relative {
-        other + self
+    fn div(self, other: f64) -> Self::Output {
+        Self {
+            rel: self.rel / other,
+            abs: self.abs / other,
+        }
     }
 }
 
-impl Add<Ratio> for Relative {
-    type Output = Self;
-
-    fn add(self, other: Ratio) -> Self {
-        Self { rel: self.rel + other, abs: self.abs }
+impl<T: Numeric> AddAssign for Relative<T> {
+    fn add_assign(&mut self, other: Self) {
+        *self = *self + other;
     }
 }
 
-impl Add<Relative> for Ratio {
-    type Output = Relative;
+impl<T: Numeric> SubAssign for Relative<T> {
+    fn sub_assign(&mut self, other: Self) {
+        *self = *self - other;
+    }
+}
 
-    fn add(self, other: Relative) -> Relative {
-        other + self
+impl<T: Numeric> MulAssign<f64> for Relative<T> {
+    fn mul_assign(&mut self, other: f64) {
+        *self = *self * other;
     }
 }
 
-sub_impl!(Relative - Relative -> Relative);
-sub_impl!(Length - Ratio -> Relative);
-sub_impl!(Ratio - Length -> Relative);
-sub_impl!(Relative - Length -> Relative);
-sub_impl!(Length - Relative -> Relative);
-sub_impl!(Relative - Ratio -> Relative);
-sub_impl!(Ratio - Relative -> Relative);
+impl<T: Numeric> DivAssign<f64> for Relative<T> {
+    fn div_assign(&mut self, other: f64) {
+        *self = *self * other;
+    }
+}
 
-impl Mul<f64> for Relative {
-    type Output = Self;
+impl<T: Numeric> Add<T> for Ratio {
+    type Output = Relative<T>;
 
-    fn mul(self, other: f64) -> Self {
-        Self {
-            rel: self.rel * other,
-            abs: self.abs * other,
-        }
+    fn add(self, other: T) -> Self::Output {
+        Relative::from(self) + Relative::from(other)
     }
 }
 
-impl Mul<Relative> for f64 {
-    type Output = Relative;
+impl<T: Numeric> Add<T> for Relative<T> {
+    type Output = Self;
 
-    fn mul(self, other: Relative) -> Relative {
-        other * self
+    fn add(self, other: T) -> Self::Output {
+        self + Relative::from(other)
     }
 }
 
-impl Div<f64> for Relative {
+impl<T: Numeric> Add<Ratio> for Relative<T> {
     type Output = Self;
 
-    fn div(self, other: f64) -> Self {
-        Self {
-            rel: self.rel / other,
-            abs: self.abs / other,
-        }
+    fn add(self, other: Ratio) -> Self::Output {
+        self + Relative::from(other)
     }
 }
-
-assign_impl!(Relative += Relative);
-assign_impl!(Relative += Length);
-assign_impl!(Relative += Ratio);
-assign_impl!(Relative -= Relative);
-assign_impl!(Relative -= Length);
-assign_impl!(Relative -= Ratio);
-assign_impl!(Relative *= f64);
-assign_impl!(Relative /= f64);
diff --git a/src/geom/scalar.rs b/src/geom/scalar.rs
index 1435654d..91225a2b 100644
--- a/src/geom/scalar.rs
+++ b/src/geom/scalar.rs
@@ -6,6 +6,16 @@ use super::*;
 #[derive(Default, Copy, Clone)]
 pub struct Scalar(pub f64);
 
+impl Numeric for Scalar {
+    fn zero() -> Self {
+        Self(0.0)
+    }
+
+    fn is_finite(self) -> bool {
+        self.0.is_finite()
+    }
+}
+
 impl From<f64> for Scalar {
     fn from(float: f64) -> Self {
         Self(float)
diff --git a/src/geom/sides.rs b/src/geom/sides.rs
index 45420c18..4539728f 100644
--- a/src/geom/sides.rs
+++ b/src/geom/sides.rs
@@ -43,7 +43,7 @@ where
     }
 }
 
-impl Sides<Relative> {
+impl Sides<Relative<Length>> {
     /// Resolve the sides relative to the given `size`.
     pub fn resolve(self, size: Size) -> Sides<Length> {
         Sides {
diff --git a/src/geom/spec.rs b/src/geom/spec.rs
index 31f93a65..3fe1793a 100644
--- a/src/geom/spec.rs
+++ b/src/geom/spec.rs
@@ -201,7 +201,7 @@ pub type Size = Spec<Length>;
 
 impl Size {
     /// The zero value.
-    pub fn zero() -> Self {
+    pub const fn zero() -> Self {
         Self { x: Length::zero(), y: Length::zero() }
     }
 
@@ -210,24 +210,19 @@ impl Size {
         self.x.fits(other.x) && self.y.fits(other.y)
     }
 
-    /// Whether both components are zero.
-    pub fn is_zero(self) -> bool {
-        self.x.is_zero() && self.y.is_zero()
-    }
-
-    /// Whether both components are finite.
-    pub fn is_finite(self) -> bool {
-        self.x.is_finite() && self.y.is_finite()
+    /// Convert to a point.
+    pub fn to_point(self) -> Point {
+        Point::new(self.x, self.y)
     }
+}
 
-    /// Whether any of the two components is infinite.
-    pub fn is_infinite(self) -> bool {
-        self.x.is_infinite() || self.y.is_infinite()
+impl Numeric for Size {
+    fn zero() -> Self {
+        Self::zero()
     }
 
-    /// Convert to a point.
-    pub fn to_point(self) -> Point {
-        Point::new(self.x, self.y)
+    fn is_finite(self) -> bool {
+        self.x.is_finite() && self.y.is_finite()
     }
 }
 
diff --git a/src/geom/transform.rs b/src/geom/transform.rs
index 8d64ebcf..c0a06e33 100644
--- a/src/geom/transform.rs
+++ b/src/geom/transform.rs
@@ -24,18 +24,18 @@ impl Transform {
         }
     }
 
-    /// A translation transform.
-    pub const fn translation(tx: Length, ty: Length) -> Self {
+    /// A translate transform.
+    pub const fn translate(tx: Length, ty: Length) -> Self {
         Self { tx, ty, ..Self::identity() }
     }
 
-    /// A scaling transform.
+    /// A scale transform.
     pub const fn scale(sx: Ratio, sy: Ratio) -> Self {
         Self { sx, sy, ..Self::identity() }
     }
 
-    /// A rotation transform.
-    pub fn rotation(angle: Angle) -> Self {
+    /// A rotate transform.
+    pub fn rotate(angle: Angle) -> Self {
         let cos = Ratio::new(angle.cos());
         let sin = Ratio::new(angle.sin());
         Self {
diff --git a/src/library/graphics/line.rs b/src/library/graphics/line.rs
index 1ca25bd9..571506c1 100644
--- a/src/library/graphics/line.rs
+++ b/src/library/graphics/line.rs
@@ -3,8 +3,10 @@ use crate::library::prelude::*;
 /// Display a line without affecting the layout.
 #[derive(Debug, Hash)]
 pub struct LineNode {
-    origin: Spec<Relative>,
-    delta: Spec<Relative>,
+    /// Where the line starts.
+    origin: Spec<Relative<Length>>,
+    /// The offset from the `origin` where the line ends.
+    delta: Spec<Relative<Length>>,
 }
 
 #[node]
@@ -15,14 +17,15 @@ impl LineNode {
     pub const THICKNESS: Length = Length::pt(1.0);
 
     fn construct(_: &mut Context, args: &mut Args) -> TypResult<Content> {
-        let origin = args.named::<Spec<Relative>>("origin")?.unwrap_or_default();
-        let delta = match args.named::<Spec<Relative>>("to")? {
+        let origin = args.named("origin")?.unwrap_or_default();
+        let delta = match args.named::<Spec<Relative<Length>>>("to")? {
             Some(to) => to.zip(origin).map(|(to, from)| to - from),
             None => {
-                let length =
-                    args.named::<Relative>("length")?.unwrap_or(Length::cm(1.0).into());
-                let angle = args.named::<Angle>("angle")?.unwrap_or_default();
+                let length = args
+                    .named::<Relative<Length>>("length")?
+                    .unwrap_or(Length::cm(1.0).into());
 
+                let angle = args.named::<Angle>("angle")?.unwrap_or_default();
                 let x = angle.cos() * length;
                 let y = angle.sin() * length;
 
diff --git a/src/library/graphics/shape.rs b/src/library/graphics/shape.rs
index 3f338d1a..9faa4c52 100644
--- a/src/library/graphics/shape.rs
+++ b/src/library/graphics/shape.rs
@@ -28,7 +28,7 @@ impl<const S: ShapeKind> ShapeNode<S> {
     /// The stroke's thickness.
     pub const THICKNESS: Length = Length::pt(1.0);
     /// How much to pad the shape's content.
-    pub const PADDING: Relative = Relative::zero();
+    pub const PADDING: Relative<Length> = Relative::zero();
 
     fn construct(_: &mut Context, args: &mut Args) -> TypResult<Content> {
         let size = match S {
diff --git a/src/library/graphics/transform.rs b/src/library/graphics/transform.rs
index 1ce91f28..eb419a7e 100644
--- a/src/library/graphics/transform.rs
+++ b/src/library/graphics/transform.rs
@@ -29,11 +29,11 @@ impl<const T: TransformKind> TransformNode<T> {
             MOVE => {
                 let tx = args.named("x")?.unwrap_or_default();
                 let ty = args.named("y")?.unwrap_or_default();
-                Transform::translation(tx, ty)
+                Transform::translate(tx, ty)
             }
             ROTATE => {
                 let angle = args.named_or_find("angle")?.unwrap_or_default();
-                Transform::rotation(angle)
+                Transform::rotate(angle)
             }
             SCALE | _ => {
                 let all = args.find()?;
@@ -62,9 +62,9 @@ impl<const T: TransformKind> Layout for TransformNode<T> {
 
         for frame in &mut frames {
             let Spec { x, y } = origin.zip(frame.size).map(|(o, s)| o.resolve(s));
-            let transform = Transform::translation(x, y)
+            let transform = Transform::translate(x, y)
                 .pre_concat(self.transform)
-                .pre_concat(Transform::translation(-x, -y));
+                .pre_concat(Transform::translate(-x, -y));
 
             Arc::make_mut(frame).transform(transform);
         }
diff --git a/src/library/layout/columns.rs b/src/library/layout/columns.rs
index 56e55d57..1cb45c37 100644
--- a/src/library/layout/columns.rs
+++ b/src/library/layout/columns.rs
@@ -14,7 +14,7 @@ pub struct ColumnsNode {
 #[node]
 impl ColumnsNode {
     /// The size of the gutter space between each column.
-    pub const GUTTER: Relative = Ratio::new(0.04).into();
+    pub const GUTTER: Relative<Length> = Ratio::new(0.04).into();
 
     fn construct(_: &mut Context, args: &mut Args) -> TypResult<Content> {
         Ok(Content::block(Self {
@@ -33,7 +33,7 @@ impl Layout for ColumnsNode {
     ) -> TypResult<Vec<Arc<Frame>>> {
         // Separating the infinite space into infinite columns does not make
         // much sense.
-        if regions.first.x.is_infinite() {
+        if !regions.first.x.is_finite() {
             return self.child.layout(ctx, regions, styles);
         }
 
diff --git a/src/library/layout/grid.rs b/src/library/layout/grid.rs
index ee485bd2..b1e5e54c 100644
--- a/src/library/layout/grid.rs
+++ b/src/library/layout/grid.rs
@@ -58,7 +58,7 @@ pub enum TrackSizing {
     Auto,
     /// A track size specified in absolute terms and relative to the parent's
     /// size.
-    Relative(Relative),
+    Relative(Relative<Length>),
     /// A track size specified as a fraction of the remaining free space in the
     /// parent.
     Fractional(Fraction),
@@ -422,7 +422,7 @@ impl<'a> GridLayouter<'a> {
     fn layout_relative_row(
         &mut self,
         ctx: &mut Context,
-        v: Relative,
+        v: Relative<Length>,
         y: usize,
     ) -> TypResult<()> {
         let resolved = v.resolve(self.regions.base.y);
diff --git a/src/library/layout/pad.rs b/src/library/layout/pad.rs
index 1ec5f124..b7470540 100644
--- a/src/library/layout/pad.rs
+++ b/src/library/layout/pad.rs
@@ -4,7 +4,7 @@ use crate::library::prelude::*;
 #[derive(Debug, Hash)]
 pub struct PadNode {
     /// The amount of padding.
-    pub padding: Sides<Relative>,
+    pub padding: Sides<Relative<Length>>,
     /// The child node whose sides to pad.
     pub child: LayoutNode,
 }
@@ -54,7 +54,7 @@ impl Layout for PadNode {
 }
 
 /// Shrink a size by padding relative to the size itself.
-fn shrink(size: Size, padding: Sides<Relative>) -> Size {
+fn shrink(size: Size, padding: Sides<Relative<Length>>) -> Size {
     size - padding.resolve(size).sum_by_axis()
 }
 
@@ -77,7 +77,7 @@ fn shrink(size: Size, padding: Sides<Relative>) -> Size {
 ///   <=> w - p.rel * w - p.abs = s
 ///   <=> (1 - p.rel) * w = s + p.abs
 ///   <=> w = (s + p.abs) / (1 - p.rel)
-fn grow(size: Size, padding: Sides<Relative>) -> Size {
+fn grow(size: Size, padding: Sides<Relative<Length>>) -> Size {
     size.zip(padding.sum_by_axis())
         .map(|(s, p)| (s + p.abs).safe_div(1.0 - p.rel.get()))
 }
diff --git a/src/library/layout/page.rs b/src/library/layout/page.rs
index abe1786f..37a87ae2 100644
--- a/src/library/layout/page.rs
+++ b/src/library/layout/page.rs
@@ -16,13 +16,13 @@ impl PageNode {
     /// Whether the page is flipped into landscape orientation.
     pub const FLIPPED: bool = false;
     /// The left margin.
-    pub const LEFT: Smart<Relative> = Smart::Auto;
+    pub const LEFT: Smart<Relative<Length>> = Smart::Auto;
     /// The right margin.
-    pub const RIGHT: Smart<Relative> = Smart::Auto;
+    pub const RIGHT: Smart<Relative<Length>> = Smart::Auto;
     /// The top margin.
-    pub const TOP: Smart<Relative> = Smart::Auto;
+    pub const TOP: Smart<Relative<Length>> = Smart::Auto;
     /// The bottom margin.
-    pub const BOTTOM: Smart<Relative> = Smart::Auto;
+    pub const BOTTOM: Smart<Relative<Length>> = Smart::Auto;
     /// The page's background color.
     pub const FILL: Option<Paint> = None;
     /// How many columns the page has.
@@ -85,7 +85,7 @@ impl PageNode {
         }
 
         let mut min = width.min(height);
-        if min.is_infinite() {
+        if !min.is_finite() {
             min = Paper::A4.width();
         }
 
@@ -115,7 +115,7 @@ impl PageNode {
         }
 
         // Layout the child.
-        let regions = Regions::repeat(size, size, size.map(Length::is_finite));
+        let regions = Regions::repeat(size, size, size.map(Numeric::is_finite));
         let mut frames = child.layout(ctx, &regions, styles)?;
 
         let header = styles.get(Self::HEADER);
@@ -133,7 +133,7 @@ impl PageNode {
                     let pos = Point::new(padding.left, y);
                     let w = size.x - padding.left - padding.right;
                     let area = Size::new(w, h);
-                    let pod = Regions::one(area, area, area.map(Length::is_finite));
+                    let pod = Regions::one(area, area, area.map(Numeric::is_finite));
                     let sub = Layout::layout(&content, ctx, &pod, styles)?.remove(0);
                     Arc::make_mut(frame).push_frame(pos, sub);
                 }
diff --git a/src/library/layout/spacing.rs b/src/library/layout/spacing.rs
index 633093e9..e9837ef5 100644
--- a/src/library/layout/spacing.rs
+++ b/src/library/layout/spacing.rs
@@ -24,7 +24,7 @@ impl VNode {
 #[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
 pub enum Spacing {
     /// Spacing specified in absolute terms and relative to the parent's size.
-    Relative(Relative),
+    Relative(Relative<Length>),
     /// Spacing specified as a fraction of the remaining free space in the parent.
     Fractional(Fraction),
 }
diff --git a/src/library/mod.rs b/src/library/mod.rs
index af9ab575..7c5a519f 100644
--- a/src/library/mod.rs
+++ b/src/library/mod.rs
@@ -167,16 +167,13 @@ castable! {
 }
 
 castable! {
-    Spec<Relative>,
+    Spec<Relative<Length>>,
     Expected: "array of two relative lengths",
     Value::Array(array) => {
-        match array.as_slice() {
-            [a, b] => {
-                let a = a.clone().cast::<Relative>()?;
-                let b = b.clone().cast::<Relative>()?;
-                Spec::new(a, b)
-            },
-            _ => return Err("point array must contain exactly two entries".to_string()),
+        let mut iter = array.into_iter();
+        match (iter.next(), iter.next(), iter.next()) {
+            (Some(a), Some(b), None) => Spec::new(a.cast()?, b.cast()?),
+            _ => Err("point array must contain exactly two entries")?,
         }
     },
 }
diff --git a/src/library/structure/list.rs b/src/library/structure/list.rs
index 532ec625..c58e8648 100644
--- a/src/library/structure/list.rs
+++ b/src/library/structure/list.rs
@@ -34,11 +34,11 @@ impl<const L: ListKind> ListNode<L> {
     #[property(referenced)]
     pub const LABEL: Label = Label::Default;
     /// The spacing between the list items of a non-wide list.
-    pub const SPACING: Relative = Relative::zero();
+    pub const SPACING: Relative<Length> = Relative::zero();
     /// The indentation of each item's label.
-    pub const INDENT: Relative = Ratio::new(0.0).into();
+    pub const INDENT: Relative<Length> = Ratio::new(0.0).into();
     /// The space between the label and the body of each item.
-    pub const BODY_INDENT: Relative = Ratio::new(0.5).into();
+    pub const BODY_INDENT: Relative<Length> = Ratio::new(0.5).into();
     /// The extra padding above the list.
     pub const ABOVE: Length = Length::zero();
     /// The extra padding below the list.
diff --git a/src/library/structure/table.rs b/src/library/structure/table.rs
index 9317e43f..e01ae908 100644
--- a/src/library/structure/table.rs
+++ b/src/library/structure/table.rs
@@ -23,7 +23,7 @@ impl TableNode {
     /// The stroke's thickness.
     pub const THICKNESS: Length = Length::pt(1.0);
     /// How much to pad the cells's content.
-    pub const PADDING: Relative = Length::pt(5.0).into();
+    pub const PADDING: Relative<Length> = Length::pt(5.0).into();
 
     fn construct(_: &mut Context, args: &mut Args) -> TypResult<Content> {
         let columns = args.named("columns")?.unwrap_or_default();
diff --git a/src/library/text/deco.rs b/src/library/text/deco.rs
index a81f0374..da1a1141 100644
--- a/src/library/text/deco.rs
+++ b/src/library/text/deco.rs
@@ -26,13 +26,13 @@ impl<const L: DecoLine> DecoNode<L> {
     /// Thickness of the line's strokes (dependent on scaled font size), read
     /// from the font tables if `None`.
     #[property(shorthand)]
-    pub const THICKNESS: Option<Relative> = None;
+    pub const THICKNESS: Option<Relative<Length>> = None;
     /// Position of the line relative to the baseline (dependent on scaled font
     /// size), read from the font tables if `None`.
-    pub const OFFSET: Option<Relative> = None;
+    pub const OFFSET: Option<Relative<Length>> = None;
     /// Amount that the line will be longer or shorter than its associated text
     /// (dependent on scaled font size).
-    pub const EXTENT: Relative = Relative::zero();
+    pub const EXTENT: Relative<Length> = Relative::zero();
     /// Whether the line skips sections in which it would collide
     /// with the glyphs. Does not apply to strikethrough.
     pub const EVADE: bool = true;
@@ -66,9 +66,9 @@ impl<const L: DecoLine> Show for DecoNode<L> {
 pub struct Decoration {
     pub line: DecoLine,
     pub stroke: Option<Paint>,
-    pub thickness: Option<Relative>,
-    pub offset: Option<Relative>,
-    pub extent: Relative,
+    pub thickness: Option<Relative<Length>>,
+    pub offset: Option<Relative<Length>>,
+    pub extent: Relative<Length>,
     pub evade: bool,
 }
 
diff --git a/src/library/text/mod.rs b/src/library/text/mod.rs
index 975a4805..4a139fb3 100644
--- a/src/library/text/mod.rs
+++ b/src/library/text/mod.rs
@@ -188,7 +188,7 @@ castable! {
 
 /// The size of text.
 #[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
-pub struct FontSize(pub Relative);
+pub struct FontSize(pub Relative<Length>);
 
 impl Fold for FontSize {
     type Output = Length;
diff --git a/src/library/text/par.rs b/src/library/text/par.rs
index a05aff44..2d31cd11 100644
--- a/src/library/text/par.rs
+++ b/src/library/text/par.rs
@@ -42,11 +42,11 @@ impl ParNode {
     /// will will be hyphenated if and only if justification is enabled.
     pub const HYPHENATE: Smart<bool> = Smart::Auto;
     /// The spacing between lines (dependent on scaled font size).
-    pub const LEADING: Relative = Ratio::new(0.65).into();
+    pub const LEADING: Relative<Length> = Ratio::new(0.65).into();
     /// The extra spacing between paragraphs (dependent on scaled font size).
-    pub const SPACING: Relative = Ratio::new(0.55).into();
+    pub const SPACING: Relative<Length> = Ratio::new(0.55).into();
     /// The indent the first line of a consecutive paragraph should have.
-    pub const INDENT: Relative = Relative::zero();
+    pub const INDENT: Relative<Length> = Relative::zero();
 
     fn construct(_: &mut Context, args: &mut Args) -> TypResult<Content> {
         // The paragraph constructor is special: It doesn't create a paragraph
diff --git a/src/library/utility/color.rs b/src/library/utility/color.rs
index 409af177..75410380 100644
--- a/src/library/utility/color.rs
+++ b/src/library/utility/color.rs
@@ -8,7 +8,7 @@ pub fn rgb(_: &mut Context, args: &mut Args) -> TypResult<Value> {
         if let Some(string) = args.find::<Spanned<EcoString>>()? {
             match RgbaColor::from_str(&string.v) {
                 Ok(color) => color,
-                Err(_) => bail!(string.span, "invalid hex string"),
+                Err(msg) => bail!(string.span, msg),
             }
         } else {
             struct Component(u8);