diff --git a/src/func/helpers.rs b/src/func/helpers.rs
new file mode 100644
index 000000000..d562284f8
--- /dev/null
+++ b/src/func/helpers.rs
@@ -0,0 +1,129 @@
+use super::prelude::*;
+use std::iter::Peekable;
+use std::slice::Iter;
+
+/// Implement the function trait more concisely.
+#[macro_export]
+macro_rules! function {
+    (data: $ident:ident, $($tts:tt)*) => {
+        impl Function for $ident {
+            function!(@parse $ident, $($tts)*);
+        }
+    };
+
+    (@parse $ident:ident, parse: plain, $($tts:tt)*) => {
+        fn parse(header: &FuncHeader, body: Option<&str>, _: ParseContext)
+            -> ParseResult<Self> where Self: Sized
+        {
+            Arguments::new(header).done()?;
+            if body.is_some() {
+                err!("expected no body");
+            }
+            Ok($ident)
+        }
+        function!(@layout $($tts)*);
+    };
+
+    (
+        @parse $ident:ident,
+        parse($args:ident, $body:ident, $ctx:ident)
+        $block:block
+        $($tts:tt)*
+    ) => {
+        fn parse(header: &FuncHeader, body: Option<&str>, ctx: ParseContext)
+            -> ParseResult<Self> where Self: Sized
+        {
+            #[allow(unused_mut)] let mut $args = Arguments::new(header);
+            let $body = body;
+            let $ctx = ctx;
+            $block
+        }
+        function!(@layout $($tts)*);
+    };
+
+    (@layout layout($this:pat, $ctx:pat) $block:block) => {
+        fn layout(&self, ctx: LayoutContext) -> LayoutResult<CommandList> {
+            let $ctx = ctx;
+            let $this = self;
+            $block
+        }
+    };
+}
+
+/// Parse the body of a function.
+/// - If the function does not expect a body, use `forbidden`.
+/// - If the function can have a body, use `optional`.
+/// - If the function must have a body, use `required`.
+#[macro_export]
+macro_rules! parse {
+    (forbidden: $body:expr) => {
+        if $body.is_some() {
+            err!("unexpected body");
+        }
+    };
+
+    (optional: $body:expr, $ctx:expr) => {
+        if let Some(body) = $body {
+            Some($crate::parsing::parse(body, $ctx)?)
+        } else {
+            None
+        }
+    };
+
+    (required: $body:expr, $ctx:expr) => {
+        if let Some(body) = $body {
+            $crate::parsing::parse(body, $ctx)?
+        } else {
+            err!("expected body");
+        }
+    }
+}
+
+/// Return a formatted parsing error.
+#[macro_export]
+macro_rules! err {
+    ($($tts:tt)*) => {
+        return Err(ParseError::new(format!($($tts)*)));
+    };
+}
+
+/// Convenient interface for parsing function arguments.
+pub struct Arguments<'a> {
+    args: Peekable<Iter<'a, Expression>>,
+}
+
+impl<'a> Arguments<'a> {
+    pub fn new(header: &'a FuncHeader) -> Arguments<'a> {
+        Arguments {
+            args: header.args.iter().peekable()
+        }
+    }
+
+    pub fn get_expr(&mut self) -> ParseResult<&'a Expression> {
+        self.args.next()
+            .ok_or_else(|| ParseError::new("expected expression"))
+    }
+
+    pub fn get_ident(&mut self) -> ParseResult<&'a str> {
+        match self.get_expr()? {
+            Expression::Ident(s) => Ok(s.as_str()),
+            _ => Err(ParseError::new("expected identifier")),
+        }
+    }
+
+    pub fn get_ident_if_present(&mut self) -> ParseResult<Option<&'a str>> {
+        if self.args.peek().is_some() {
+            self.get_ident().map(|s| Some(s))
+        } else {
+            Ok(None)
+        }
+    }
+
+    pub fn done(&mut self) -> ParseResult<()> {
+        if self.args.peek().is_none() {
+            Ok(())
+        } else {
+            Err(ParseError::new("unexpected argument"))
+        }
+    }
+}
diff --git a/src/func.rs b/src/func/mod.rs
similarity index 89%
rename from src/func.rs
rename to src/func/mod.rs
index 05bbe83df..9a6fcbd14 100644
--- a/src/func.rs
+++ b/src/func/mod.rs
@@ -9,6 +9,21 @@ use crate::parsing::{ParseContext, ParseResult};
 use crate::style::TextStyle;
 use crate::syntax::{FuncHeader, SyntaxTree};
 
+#[macro_use]
+mod helpers;
+pub use helpers::Arguments;
+
+/// Useful imports for creating your own functions.
+pub mod prelude {
+    pub use crate::func::{Command, CommandList, Function};
+    pub use crate::layout::{layout_tree, Layout, LayoutContext, MultiLayout};
+    pub use crate::layout::{Flow, Alignment, LayoutError, LayoutResult};
+    pub use crate::parsing::{parse, ParseContext, ParseError, ParseResult};
+    pub use crate::syntax::{Expression, FuncHeader, SyntaxTree};
+    pub use crate::size::{Size, Size2D, SizeBox};
+    pub use super::helpers::*;
+}
+
 /// Typesetting function types.
 ///
 /// These types have to be able to parse tokens into themselves and store the
diff --git a/src/library/align.rs b/src/library/align.rs
deleted file mode 100644
index cc41f295d..000000000
--- a/src/library/align.rs
+++ /dev/null
@@ -1,49 +0,0 @@
-use super::prelude::*;
-use crate::layout::Alignment;
-
-/// Allows to align content in different ways.
-#[derive(Debug, PartialEq)]
-pub struct AlignFunc {
-    alignment: Alignment,
-    body: Option<SyntaxTree>,
-}
-
-impl Function for AlignFunc {
-    fn parse(header: &FuncHeader, body: Option<&str>, ctx: ParseContext) -> ParseResult<Self>
-    where Self: Sized {
-        if header.args.len() != 1 || !header.kwargs.is_empty() {
-            return err("align: expected exactly one positional argument");
-        }
-
-        let alignment = if let Expression::Ident(ident) = &header.args[0] {
-            match ident.as_str() {
-                "left" => Alignment::Left,
-                "right" => Alignment::Right,
-                "center" => Alignment::Center,
-                s => return err(format!("invalid alignment specifier: '{}'", s)),
-            }
-        } else {
-            return err(format!(
-                "expected alignment specifier, found: '{}'",
-                header.args[0]
-            ));
-        };
-
-        let body = parse_maybe_body(body, ctx)?;
-
-        Ok(AlignFunc { alignment, body })
-    }
-
-    fn layout(&self, ctx: LayoutContext) -> LayoutResult<CommandList> {
-        if let Some(body) = &self.body {
-            let layouts = layout_tree(body, LayoutContext {
-                alignment: self.alignment,
-                .. ctx
-            })?;
-
-            Ok(commands![Command::AddMany(layouts)])
-        } else {
-            Ok(commands![Command::SetAlignment(self.alignment)])
-        }
-    }
-}
diff --git a/src/library/boxed.rs b/src/library/boxed.rs
deleted file mode 100644
index 71a184a66..000000000
--- a/src/library/boxed.rs
+++ /dev/null
@@ -1,51 +0,0 @@
-use super::prelude::*;
-use crate::layout::Flow;
-
-/// Wraps content into a box.
-#[derive(Debug, PartialEq)]
-pub struct BoxFunc {
-    body: SyntaxTree,
-    flow: Flow,
-}
-
-impl Function for BoxFunc {
-    fn parse(header: &FuncHeader, body: Option<&str>, ctx: ParseContext) -> ParseResult<Self>
-    where Self: Sized {
-        let flow = if header.args.is_empty() {
-            Flow::Vertical
-        } else if header.args.len() == 1 {
-            if let Expression::Ident(ident) = &header.args[0] {
-                match ident.as_str() {
-                    "vertical" => Flow::Vertical,
-                    "horizontal" => Flow::Horizontal,
-                    f => return err(format!("invalid flow specifier: '{}'", f)),
-                }
-            } else {
-                return err(format!(
-                    "expected alignment specifier, found: '{}'",
-                    header.args[0]
-                ));
-            }
-        } else {
-            return err("box: expected flow specifier or no arguments");
-        };
-
-        if let Some(body) = body {
-            Ok(BoxFunc {
-                body: parse(body, ctx)?,
-                flow,
-            })
-        } else {
-            err("box: expected body")
-        }
-    }
-
-    fn layout(&self, ctx: LayoutContext) -> LayoutResult<CommandList> {
-        let layout = layout_tree(&self.body, LayoutContext {
-            flow: self.flow,
-            .. ctx
-        })?;
-
-        Ok(commands![Command::AddMany(layout)])
-    }
-}
diff --git a/src/library/breaks.rs b/src/library/breaks.rs
deleted file mode 100644
index a622350f2..000000000
--- a/src/library/breaks.rs
+++ /dev/null
@@ -1,47 +0,0 @@
-use super::prelude::*;
-
-/// Ends the current line.
-#[derive(Debug, PartialEq)]
-pub struct LinebreakFunc;
-
-impl Function for LinebreakFunc {
-    fn parse(header: &FuncHeader, body: Option<&str>, _: ParseContext) -> ParseResult<Self>
-    where Self: Sized {
-        if has_arguments(header) {
-            return err("linebreak: expected no arguments");
-        }
-
-        if body.is_some() {
-            return err("linebreak: expected no body");
-        }
-
-        Ok(LinebreakFunc)
-    }
-
-    fn layout(&self, _: LayoutContext) -> LayoutResult<CommandList> {
-        Ok(commands![Command::FinishFlexRun])
-    }
-}
-
-/// Ends the current page.
-#[derive(Debug, PartialEq)]
-pub struct PagebreakFunc;
-
-impl Function for PagebreakFunc {
-    fn parse(header: &FuncHeader, body: Option<&str>, _: ParseContext) -> ParseResult<Self>
-    where Self: Sized {
-        if has_arguments(header) {
-            return err("pagebreak: expected no arguments");
-        }
-
-        if body.is_some() {
-            return err("pagebreak: expected no body");
-        }
-
-        Ok(PagebreakFunc)
-    }
-
-    fn layout(&self, _: LayoutContext) -> LayoutResult<CommandList> {
-        Ok(commands![Command::FinishLayout])
-    }
-}
diff --git a/src/library/mod.rs b/src/library/mod.rs
index 784ef2041..74f77204d 100644
--- a/src/library/mod.rs
+++ b/src/library/mod.rs
@@ -2,64 +2,29 @@
 
 use crate::func::Scope;
 
-mod align;
-mod boxed;
-mod breaks;
-mod spacing;
-mod styles;
+mod structure;
+mod style;
 
-/// Useful imports for creating your own functions.
-pub mod prelude {
-    pub use crate::func::{Command, CommandList, Function};
-    pub use crate::layout::{layout_tree, Layout, LayoutContext, MultiLayout};
-    pub use crate::layout::{LayoutError, LayoutResult};
-    pub use crate::parsing::{parse, ParseContext, ParseError, ParseResult};
-    pub use crate::syntax::{Expression, FuncHeader, SyntaxTree};
-    pub use super::helpers::*;
-}
-
-pub use align::AlignFunc;
-pub use boxed::BoxFunc;
-pub use breaks::{LinebreakFunc, PagebreakFunc};
-pub use spacing::{HorizontalSpaceFunc, VerticalSpaceFunc};
-pub use styles::{BoldFunc, ItalicFunc, MonospaceFunc};
+pub use structure::*;
+pub use style::*;
 
 /// Create a scope with all standard functions.
 pub fn std() -> Scope {
     let mut std = Scope::new();
-    std.add::<AlignFunc>("align");
-    std.add::<BoxFunc>("box");
 
-    std.add::<LinebreakFunc>("line.break");
-    std.add::<LinebreakFunc>("n");
-    std.add::<PagebreakFunc>("page.break");
+    std.add::<Align>("align");
+    std.add::<Boxed>("box");
 
-    std.add::<HorizontalSpaceFunc>("h");
-    std.add::<VerticalSpaceFunc>("v");
+    std.add::<Linebreak>("line.break");
+    std.add::<Linebreak>("n");
+    std.add::<Pagebreak>("page.break");
+
+    std.add::<HorizontalSpace>("h");
+    std.add::<VerticalSpace>("v");
+
+    std.add::<Bold>("bold");
+    std.add::<Italic>("italic");
+    std.add::<Monospace>("mono");
 
-    std.add::<BoldFunc>("bold");
-    std.add::<ItalicFunc>("italic");
-    std.add::<MonospaceFunc>("mono");
     std
 }
-
-/// Helpers for writing custom functions.
-pub mod helpers {
-    use super::prelude::*;
-
-    pub fn has_arguments(header: &FuncHeader) -> bool {
-        !header.args.is_empty() || !header.kwargs.is_empty()
-    }
-
-    pub fn parse_maybe_body(body: Option<&str>, ctx: ParseContext) -> ParseResult<Option<SyntaxTree>> {
-        if let Some(body) = body {
-            Ok(Some(parse(body, ctx)?))
-        } else {
-            Ok(None)
-        }
-    }
-
-    pub fn err<S: Into<String>, T>(message: S) -> ParseResult<T> {
-        Err(ParseError::new(message))
-    }
-}
diff --git a/src/library/spacing.rs b/src/library/spacing.rs
deleted file mode 100644
index 91288edcb..000000000
--- a/src/library/spacing.rs
+++ /dev/null
@@ -1,76 +0,0 @@
-use std::marker::PhantomData;
-use super::prelude::*;
-use crate::size::Size;
-
-/// Adds vertical space.
-pub type VerticalSpaceFunc = SpaceFunc<SpaceVertical>;
-
-/// Adds horizontal space.
-pub type HorizontalSpaceFunc = SpaceFunc<SpaceHorizontal>;
-
-/// Adds generic space.
-#[derive(Debug, PartialEq)]
-pub struct SpaceFunc<F: SpaceFlow> {
-    spacing: Spacing,
-    _phantom: PhantomData<F>,
-}
-
-/// Absolute or font-relative spacing.
-#[derive(Debug, PartialEq)]
-enum Spacing {
-    Absolute(Size),
-    Relative(f32),
-}
-
-impl<F: SpaceFlow> Function for SpaceFunc<F> {
-    fn parse(header: &FuncHeader, body: Option<&str>, _: ParseContext) -> ParseResult<Self>
-    where Self: Sized {
-        if header.args.len() != 1 || !header.kwargs.is_empty() {
-            return err("align: expected exactly one positional argument");
-        }
-
-        let spacing = match header.args[0] {
-            Expression::Size(s) => Spacing::Absolute(s),
-            Expression::Number(f) => Spacing::Relative(f as f32),
-            _ => return err("space: expected size or number"),
-        };
-
-        if body.is_some() {
-            return err("space: expected no body");
-        }
-
-        Ok(SpaceFunc {
-            spacing,
-            _phantom: PhantomData,
-        })
-    }
-
-    fn layout(&self, ctx: LayoutContext) -> LayoutResult<CommandList> {
-        let space = match self.spacing {
-            Spacing::Absolute(s) => s,
-            Spacing::Relative(f) => Size::pt(f * ctx.style.font_size),
-        };
-
-        Ok(commands![F::cmd(space)])
-    }
-}
-
-pub trait SpaceFlow: std::fmt::Debug + PartialEq + 'static {
-    fn cmd(space: Size) -> Command<'static>;
-}
-
-#[derive(Debug, PartialEq)]
-pub struct SpaceVertical;
-impl SpaceFlow for SpaceVertical {
-    fn cmd(space: Size) -> Command<'static> {
-        Command::Add(Layout::empty(Size::zero(), space))
-    }
-}
-
-#[derive(Debug, PartialEq)]
-pub struct SpaceHorizontal;
-impl SpaceFlow for SpaceHorizontal {
-    fn cmd(space: Size) -> Command<'static> {
-        Command::AddFlex(Layout::empty(space, Size::zero()))
-    }
-}
diff --git a/src/library/structure.rs b/src/library/structure.rs
new file mode 100644
index 000000000..ae05a12be
--- /dev/null
+++ b/src/library/structure.rs
@@ -0,0 +1,148 @@
+use crate::func::prelude::*;
+
+/// Ends the current page.
+#[derive(Debug, PartialEq)]
+pub struct Pagebreak;
+
+function! {
+    data: Pagebreak,
+    parse: plain,
+
+    layout(_, _) {
+        Ok(commands![Command::FinishLayout])
+    }
+}
+
+/// Ends the current line.
+#[derive(Debug, PartialEq)]
+pub struct Linebreak;
+
+function! {
+    data: Linebreak,
+    parse: plain,
+
+    layout(_, _) {
+        Ok(commands![Command::FinishFlexRun])
+    }
+}
+
+/// Aligns content in different ways.
+#[derive(Debug, PartialEq)]
+pub struct Align {
+    body: Option<SyntaxTree>,
+    alignment: Alignment,
+}
+
+function! {
+    data: Align,
+
+    parse(args, body, ctx) {
+        let body = parse!(optional: body, ctx);
+        let alignment = match args.get_ident()? {
+            "left" => Alignment::Left,
+            "right" => Alignment::Right,
+            "center" => Alignment::Center,
+            s => err!("invalid alignment specifier: {}", s),
+        };
+        args.done()?;
+
+        Ok(Align {
+            body,
+            alignment,
+        })
+    }
+
+    layout(this, ctx) {
+        Ok(commands![match &this.body {
+            Some(body) => {
+                Command::AddMany(layout_tree(body, LayoutContext {
+                    alignment: this.alignment,
+                    .. ctx
+                })?)
+            }
+            None => Command::SetAlignment(this.alignment)
+        }])
+    }
+}
+
+/// Layouts content into a box.
+#[derive(Debug, PartialEq)]
+pub struct Boxed {
+    body: SyntaxTree,
+    flow: Flow,
+}
+
+function! {
+    data: Boxed,
+
+    parse(args, body, ctx) {
+        let body = parse!(required: body, ctx);
+
+        let mut flow = Flow::Vertical;
+        if let Some(ident) = args.get_ident_if_present()? {
+            flow = match ident {
+                "vertical" => Flow::Vertical,
+                "horizontal" => Flow::Horizontal,
+                f => err!("invalid flow specifier: {}", f),
+            };
+        }
+        args.done()?;
+
+        Ok(Boxed {
+            body,
+            flow,
+        })
+    }
+
+    layout(this, ctx) {
+        Ok(commands![
+            Command::AddMany(layout_tree(&this.body, LayoutContext {
+                flow: this.flow,
+                .. ctx
+            })?)
+        ])
+    }
+}
+
+macro_rules! spacefunc {
+    ($ident:ident, $name:expr, $var:ident => $command:expr) => {
+        /// Adds whitespace.
+        #[derive(Debug, PartialEq)]
+        pub struct $ident(Spacing);
+
+        function! {
+            data: $ident,
+
+            parse(args, body, _ctx) {
+                parse!(forbidden: body);
+
+                let spacing = match args.get_expr()? {
+                    Expression::Size(s) => Spacing::Absolute(*s),
+                    Expression::Number(f) => Spacing::Relative(*f as f32),
+                    _ => err!("invalid spacing, expected size or number"),
+                };
+
+                Ok($ident(spacing))
+            }
+
+            layout(this, ctx) {
+                let $var = match this.0 {
+                    Spacing::Absolute(s) => s,
+                    Spacing::Relative(f) => Size::pt(f * ctx.style.font_size),
+                };
+
+                Ok(commands![$command])
+            }
+        }
+    };
+}
+
+/// Absolute or font-relative spacing.
+#[derive(Debug, PartialEq)]
+enum Spacing {
+    Absolute(Size),
+    Relative(f32),
+}
+
+spacefunc!(HorizontalSpace, "h", space => Command::AddFlex(Layout::empty(space, Size::zero())));
+spacefunc!(VerticalSpace, "v", space => Command::Add(Layout::empty(Size::zero(), space)));
diff --git a/src/library/style.rs b/src/library/style.rs
new file mode 100644
index 000000000..397375a48
--- /dev/null
+++ b/src/library/style.rs
@@ -0,0 +1,39 @@
+use crate::func::prelude::*;
+use toddle::query::FontClass;
+
+macro_rules! stylefunc {
+    ($ident:ident) => {
+        /// Styles text.
+        #[derive(Debug, PartialEq)]
+        pub struct $ident {
+            body: Option<SyntaxTree>
+        }
+
+        function! {
+            data: $ident,
+
+            parse(args, body, ctx) {
+                args.done()?;
+                Ok($ident { body: parse!(optional: body, ctx) })
+            }
+
+            layout(this, ctx) {
+                let mut new_style = ctx.style.clone();
+                new_style.toggle_class(FontClass::$ident);
+
+                Ok(match &this.body {
+                    Some(body) => commands![
+                        Command::SetStyle(new_style),
+                        Command::Layout(body),
+                        Command::SetStyle(ctx.style.clone()),
+                    ],
+                    None => commands![Command::SetStyle(new_style)]
+                })
+            }
+        }
+    };
+}
+
+stylefunc!(Italic);
+stylefunc!(Bold);
+stylefunc!(Monospace);
diff --git a/src/library/styles.rs b/src/library/styles.rs
deleted file mode 100644
index bc84ac3b4..000000000
--- a/src/library/styles.rs
+++ /dev/null
@@ -1,65 +0,0 @@
-use toddle::query::FontClass;
-
-use super::prelude::*;
-
-macro_rules! style_func {
-    (
-        $(#[$outer:meta])*
-        pub struct $struct:ident { $name:expr },
-        $style:ident => $class:ident
-    ) => {
-        $(#[$outer])*
-        #[derive(Debug, PartialEq)]
-        pub struct $struct {
-            body: Option<SyntaxTree>
-        }
-
-        impl Function for $struct {
-            fn parse(header: &FuncHeader, body: Option<&str>, ctx: ParseContext)
-                -> ParseResult<Self> where Self: Sized {
-                // Accept only invocations without arguments and with body.
-                if has_arguments(header) {
-                    return err(format!("{}: expected no arguments", $name));
-                }
-
-                let body = parse_maybe_body(body, ctx)?;
-
-                Ok($struct { body })
-            }
-
-            fn layout(&self, ctx: LayoutContext) -> LayoutResult<CommandList> {
-                let mut new_style = ctx.style.clone();
-                new_style.toggle_class(FontClass::$class);
-
-                if let Some(body) = &self.body {
-                    let saved_style = ctx.style.clone();
-                    Ok(commands![
-                        Command::SetStyle(new_style),
-                        Command::Layout(body),
-                        Command::SetStyle(saved_style),
-                    ])
-                } else {
-                    Ok(commands![Command::SetStyle(new_style)])
-                }
-            }
-        }
-    };
-}
-
-style_func! {
-    /// Typesets text in bold.
-    pub struct BoldFunc { "bold" },
-    style => Bold
-}
-
-style_func! {
-    /// Typesets text in italics.
-    pub struct ItalicFunc { "italic" },
-    style => Italic
-}
-
-style_func! {
-    /// Typesets text in monospace.
-    pub struct MonospaceFunc { "mono" },
-    style => Monospace
-}