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//! Dynamic typesetting functions.
use std::any::Any;
use std::collections::HashMap;
use std::fmt::Debug;
use crate::syntax::{Token, FuncHeader, Expression};
use crate::parsing::ParseResult;
/// An optional iterator over the tokens of a function body.
pub type BodyTokens<'a> = Option<Box<dyn Iterator<Item=Token<'a>> + 'a>>;
/// Parser functions.
pub type ParseFunc = dyn Fn(&FuncHeader, BodyTokens<'_>, &Scope)
-> ParseResult<Box<dyn Function>>;
/// Types that act as functions.
///
/// 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 function.
fn parse(header: &FuncHeader, tokens: BodyTokens<'_>, scope: &Scope)
-> ParseResult<Self> where Self: Sized;
/// Execute the function and optionally yield a return value.
fn typeset(&self, header: &FuncHeader) -> Option<Expression>;
}
/// A map from identifiers to functions.
pub struct Scope {
parsers: HashMap<String, Box<ParseFunc>>,
}
impl Scope {
/// Create a new empty scope.
pub fn new() -> Scope {
Scope { parsers: HashMap::new() }
}
/// Add a function type to the scope with a given name.
pub fn add<F: Function + 'static>(&mut self, name: &str) {
self.parsers.insert(
name.to_owned(),
Box::new(|header, tokens, scope| match F::parse(header, tokens, scope) {
Ok(func) => Ok(Box::new(func)),
Err(err) => Err(err),
})
);
}
/// Return the parser with the given name if there is one.
pub fn get_parser(&self, name: &str) -> Option<&ParseFunc> {
self.parsers.get(name).map(|x| &**x)
}
}
/// 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
}
}
}
impl PartialEq for dyn Function {
fn eq(&self, other: &dyn Function) -> bool {
self.help_eq(other)
}
}
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