Introduce a set of macros for writing functions more concisely 🎁

1 files changed, 187 insertions, 0 deletions

diff --git a/src/func/mod.rs b/src/func/mod.rs
new file mode 100644
index 00000000..9a6fcbd1
--- /dev/null
+++ b/src/func/mod.rs
@@ -0,0 +1,187 @@
+//! Dynamic typesetting functions.
+
+use std::any::Any;
+use std::collections::HashMap;
+use std::fmt::{self, Debug, Formatter};
+
+use crate::layout::{Layout, LayoutContext, Alignment, LayoutResult, MultiLayout};
+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
+/// relevant information from the parsing to do their role in typesetting later.
+///
+/// The trait `FunctionBounds` is automatically implemented for types which can
+/// be used as functions, that is they fulfill the bounds `Debug + PartialEq +
+/// 'static`.
+pub trait Function: FunctionBounds {
+    /// Parse the header and body into this function given a context.
+    fn parse(header: &FuncHeader, body: Option<&str>, ctx: ParseContext) -> ParseResult<Self>
+    where Self: Sized;
+
+    /// Layout this function given a context.
+    ///
+    /// Returns optionally the resulting layout and a new context if changes to
+    /// the context should be made.
+    fn layout(&self, ctx: LayoutContext) -> LayoutResult<CommandList>;
+}
+
+impl PartialEq for dyn Function {
+    fn eq(&self, other: &dyn Function) -> bool {
+        self.help_eq(other)
+    }
+}
+
+/// A helper trait that describes requirements for types that can implement
+/// [`Function`].
+///
+/// Automatically implemented for all types which fulfill to the bounds `Debug +
+/// PartialEq + 'static`. There should be no need to implement this manually.
+pub trait FunctionBounds: Debug {
+    /// Cast self into `Any`.
+    fn help_cast_as_any(&self) -> &dyn Any;
+
+    /// Compare self with another function.
+    fn help_eq(&self, other: &dyn Function) -> bool;
+}
+
+impl<T> FunctionBounds for T
+where T: Debug + PartialEq + 'static
+{
+    fn help_cast_as_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn help_eq(&self, other: &dyn Function) -> bool {
+        if let Some(other) = other.help_cast_as_any().downcast_ref::<Self>() {
+            self == other
+        } else {
+            false
+        }
+    }
+}
+
+/// A sequence of commands requested for execution by a function.
+#[derive(Debug)]
+pub struct CommandList<'a> {
+    pub commands: Vec<Command<'a>>,
+}
+
+impl<'a> CommandList<'a> {
+    /// Create an empty command list.
+    pub fn new() -> CommandList<'a> {
+        CommandList { commands: vec![] }
+    }
+
+    /// Create a command list with commands from a vector.
+    pub fn from_vec(commands: Vec<Command<'a>>) -> CommandList<'a> {
+        CommandList { commands }
+    }
+
+    /// Add a command to the sequence.
+    pub fn add(&mut self, command: Command<'a>) {
+        self.commands.push(command);
+    }
+
+    /// Whether there are any commands in this sequence.
+    pub fn is_empty(&self) -> bool {
+        self.commands.is_empty()
+    }
+}
+
+impl<'a> IntoIterator for CommandList<'a> {
+    type Item = Command<'a>;
+    type IntoIter = std::vec::IntoIter<Command<'a>>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.commands.into_iter()
+    }
+}
+
+impl<'a> IntoIterator for &'a CommandList<'a> {
+    type Item = &'a Command<'a>;
+    type IntoIter = std::slice::Iter<'a, Command<'a>>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.commands.iter()
+    }
+}
+
+/// Commands requested for execution by functions.
+#[derive(Debug)]
+pub enum Command<'a> {
+    Layout(&'a SyntaxTree),
+    Add(Layout),
+    AddMany(MultiLayout),
+    AddFlex(Layout),
+    SetAlignment(Alignment),
+    SetStyle(TextStyle),
+    FinishLayout,
+    FinishFlexRun,
+}
+
+macro_rules! commands {
+    ($($x:expr),*$(,)*) => ({
+        $crate::func::CommandList::from_vec(vec![$($x,)*])
+    });
+}
+
+/// A map from identifiers to functions.
+pub struct Scope {
+    parsers: HashMap<String, Box<ParseFunc>>,
+}
+
+/// A function which parses a function invocation into a function type.
+type ParseFunc = dyn Fn(&FuncHeader, Option<&str>, ParseContext) -> ParseResult<Box<dyn Function>>;
+
+impl Scope {
+    /// Create a new empty scope.
+    pub fn new() -> Scope {
+        Scope {
+            parsers: HashMap::new(),
+        }
+    }
+
+    /// Create a new scope with the standard functions contained.
+    pub fn with_std() -> Scope {
+        crate::library::std()
+    }
+
+    /// Add a function type to the scope giving it a name.
+    pub fn add<F: Function + 'static>(&mut self, name: &str) {
+        self.parsers.insert(
+            name.to_owned(),
+            Box::new(|h, b, c| F::parse(h, b, c).map(|func| Box::new(func) as Box<dyn Function>)),
+        );
+    }
+
+    /// Return the parser with the given name if there is one.
+    pub(crate) fn get_parser(&self, name: &str) -> Option<&ParseFunc> {
+        self.parsers.get(name).map(|x| &**x)
+    }
+}
+
+impl Debug for Scope {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        write!(f, "Scope ")?;
+        write!(f, "{:?}", self.parsers.keys())
+    }
+}