4 files changed, 186 insertions, 3 deletions
diff --git a/src/eval/mod.rs b/src/eval/mod.rs
index 65fc71c4..d21fbc7f 100644
--- a/src/eval/mod.rs
+++ b/src/eval/mod.rs
@@ -2,8 +2,10 @@
 
 mod dict;
 mod scope;
+mod state;
 mod value;
 
 pub use dict::*;
 pub use scope::*;
+pub use state::*;
 pub use value::*;
diff --git a/src/eval/scope.rs b/src/eval/scope.rs
index 8e6576d1..d4b24880 100644
--- a/src/eval/scope.rs
+++ b/src/eval/scope.rs
@@ -6,6 +6,7 @@ use std::fmt::{self, Debug, Formatter};
 use super::value::FuncValue;
 
 /// A map from identifiers to functions.
+#[derive(Clone, PartialEq)]
 pub struct Scope {
     functions: HashMap<String, FuncValue>,
 }
diff --git a/src/eval/state.rs b/src/eval/state.rs
new file mode 100644
index 00000000..d6e0b195
--- /dev/null
+++ b/src/eval/state.rs
@@ -0,0 +1,180 @@
+//! State.
+
+use fontdock::{fallback, FallbackTree, FontStretch, FontStyle, FontVariant, FontWeight};
+
+use super::Scope;
+use crate::geom::{Insets, Linear, Sides, Size};
+use crate::layout::{Dir, GenAlign, LayoutAlign, LayoutSystem};
+use crate::length::Length;
+use crate::paper::{Paper, PaperClass, PAPER_A4};
+
+/// The active evaluation state.
+#[derive(Debug, Clone, PartialEq)]
+pub struct State {
+    /// The scope that contains function definitions.
+    pub scope: Scope,
+    /// The text state.
+    pub text: TextState,
+    /// The page state.
+    pub page: PageState,
+    /// The active layouting system.
+    pub sys: LayoutSystem,
+    /// The active alignments.
+    pub align: LayoutAlign,
+}
+
+impl Default for State {
+    fn default() -> Self {
+        Self {
+            scope: crate::library::_std(),
+            text: TextState::default(),
+            page: PageState::default(),
+            sys: LayoutSystem::new(Dir::LTR, Dir::TTB),
+            align: LayoutAlign::new(GenAlign::Start, GenAlign::Start),
+        }
+    }
+}
+
+/// Defines which fonts to use and how to space text.
+#[derive(Debug, Clone, PartialEq)]
+pub struct TextState {
+    /// A tree of font family names and generic class names.
+    pub fallback: FallbackTree,
+    /// The selected font variant.
+    pub variant: FontVariant,
+    /// Whether the strong toggle is active or inactive. This determines
+    /// whether the next `*` adds or removes font weight.
+    pub strong: bool,
+    /// Whether the emphasis toggle is active or inactive. This determines
+    /// whether the next `_` makes italic or non-italic.
+    pub emph: bool,
+    /// The font size.
+    pub font_size: FontSize,
+    /// The word spacing (relative to the the font size).
+    pub word_spacing: Linear,
+    /// The line spacing (relative to the the font size).
+    pub line_spacing: Linear,
+    /// The paragraphs spacing (relative to the the font size).
+    pub par_spacing: Linear,
+}
+
+impl TextState {
+    /// The absolute font size.
+    pub fn font_size(&self) -> f64 {
+        self.font_size.eval()
+    }
+
+    /// The absolute word spacing.
+    pub fn word_spacing(&self) -> f64 {
+        self.word_spacing.eval(self.font_size())
+    }
+
+    /// The absolute line spacing.
+    pub fn line_spacing(&self) -> f64 {
+        self.line_spacing.eval(self.font_size())
+    }
+
+    /// The absolute paragraph spacing.
+    pub fn paragraph_spacing(&self) -> f64 {
+        self.par_spacing.eval(self.font_size())
+    }
+}
+
+impl Default for TextState {
+    fn default() -> Self {
+        Self {
+            fallback: fallback! {
+                list: ["sans-serif"],
+                classes: {
+                    "serif" => ["source serif pro", "noto serif"],
+                    "sans-serif" => ["source sans pro", "noto sans"],
+                    "monospace" => ["source code pro", "noto sans mono"],
+                    "math" => ["latin modern math", "serif"],
+                },
+                base: [
+                    "source sans pro", "noto sans", "segoe ui emoji",
+                    "noto emoji", "latin modern math",
+                ],
+            },
+            variant: FontVariant {
+                style: FontStyle::Normal,
+                weight: FontWeight::REGULAR,
+                stretch: FontStretch::Normal,
+            },
+            strong: false,
+            emph: false,
+            font_size: FontSize::abs(Length::pt(11.0).as_raw()),
+            word_spacing: Linear::rel(0.25),
+            line_spacing: Linear::rel(0.2),
+            par_spacing: Linear::rel(0.5),
+        }
+    }
+}
+
+/// The font size, defined by base and scale.
+#[derive(Debug, Clone, PartialEq)]
+pub struct FontSize {
+    /// The base font size, updated whenever the font size is set absolutely.
+    pub base: f64,
+    /// The scale to apply on the base font size, updated when the font size
+    /// is set relatively.
+    pub scale: Linear,
+}
+
+impl FontSize {
+    /// Create a new font size.
+    pub fn new(base: f64, scale: Linear) -> Self {
+        Self { base, scale }
+    }
+
+    /// Create a new font size with the given `base` and a scale of `1.0`.
+    pub fn abs(base: f64) -> Self {
+        Self::new(base, Linear::rel(1.0))
+    }
+
+    /// Compute the absolute font size.
+    pub fn eval(&self) -> f64 {
+        self.scale.eval(self.base)
+    }
+}
+
+/// Defines the size and margins of a page.
+#[derive(Debug, Copy, Clone, PartialEq)]
+pub struct PageState {
+    /// The class of this page.
+    pub class: PaperClass,
+    /// The width and height of the page.
+    pub size: Size,
+    /// The amount of white space in the order [left, top, right, bottom]. If a
+    /// side is set to `None`, the default for the paper class is used.
+    pub margins: Sides<Option<Linear>>,
+}
+
+impl PageState {
+    /// The default page style for the given paper.
+    pub fn new(paper: Paper) -> Self {
+        Self {
+            class: paper.class,
+            size: paper.size(),
+            margins: Sides::uniform(None),
+        }
+    }
+
+    /// The absolute insets.
+    pub fn insets(&self) -> Insets {
+        let Size { width, height } = self.size;
+        let default = self.class.default_margins();
+        Insets {
+            x0: -self.margins.left.unwrap_or(default.left).eval(width),
+            y0: -self.margins.top.unwrap_or(default.top).eval(height),
+            x1: -self.margins.right.unwrap_or(default.right).eval(width),
+            y1: -self.margins.bottom.unwrap_or(default.bottom).eval(height),
+        }
+    }
+}
+
+impl Default for PageState {
+    fn default() -> Self {
+        Self::new(PAPER_A4)
+    }
+}
diff --git a/src/eval/value.rs b/src/eval/value.rs
index f6c1fcd7..f88c0704 100644
--- a/src/eval/value.rs
+++ b/src/eval/value.rs
@@ -12,7 +12,7 @@ use crate::geom::Linear;
 use crate::layout::{Command, Commands, Dir, LayoutContext, SpecAlign};
 use crate::paper::Paper;
 use crate::syntax::{Ident, Span, SpanWith, Spanned, SynNode, SynTree};
-use crate::{DynFuture, Feedback, Pass};
+use crate::{DynFuture, Feedback};
 
 /// A computational value.
 #[derive(Clone, PartialEq)]
@@ -149,13 +149,13 @@ impl Debug for Value {
 pub struct FuncValue(pub Rc<FuncType>);
 
 /// The signature of executable functions.
-type FuncType = dyn Fn(Span, DictValue, LayoutContext<'_>) -> DynFuture<Pass<Value>>;
+type FuncType = dyn Fn(DictValue, &mut LayoutContext) -> DynFuture<Value>;
 
 impl FuncValue {
     /// Create a new function value from a rust function or closure.
     pub fn new<F: 'static>(f: F) -> Self
     where
-        F: Fn(Span, DictValue, LayoutContext<'_>) -> DynFuture<Pass<Value>>,
+        F: Fn(DictValue, &mut LayoutContext) -> DynFuture<Value>,
     {
         Self(Rc::new(f))
     }