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|
//! Helper types and macros for creating custom functions.
use super::prelude::*;
use Expression::*;
/// Lets you implement the function trait more concisely.
#[macro_export]
macro_rules! function {
(data: $ident:ident, $($tts:tt)*) => (
#[allow(unused_imports)]
use $crate::func::prelude::*;
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 {
ArgParser::new(&header.args).done()?;
if body.is_some() {
perr!("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 = ArgParser::new(&header.args);
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() {
perr!("unexpected body");
}
};
(optional: $body:expr, $ctx:expr) => (
if let Some(body) = $body {
Some($crate::syntax::parse(body, $ctx)?)
} else {
None
}
);
(required: $body:expr, $ctx:expr) => (
if let Some(body) = $body {
$crate::syntax::parse(body, $ctx)?
} else {
perr!("expected body");
}
)
}
/// Early-return with a formatted parsing error or yield
/// an error expression without returning when prefixed with `@`.
#[macro_export]
macro_rules! perr {
(@$($tts:tt)*) => ($crate::syntax::ParseError::new(format!($($tts)*)));
($($tts:tt)*) => (return Err(perr!(@$($tts)*)););
}
/// Early-return with a formatted layouting error or yield
/// an error expression without returning when prefixed with `@`.
#[macro_export]
macro_rules! lerr {
(@$($tts:tt)*) => ($crate::layout::LayoutError::new(format!($($tts)*)));
($($tts:tt)*) => (return Err(lerr!(@$($tts)*)););
}
/// Easy parsing of function arguments.
pub struct ArgParser<'a> {
args: &'a FuncArgs,
positional_index: usize,
}
impl<'a> ArgParser<'a> {
pub fn new(args: &'a FuncArgs) -> ArgParser<'a> {
ArgParser {
args,
positional_index: 0,
}
}
/// Get the next positional argument of the given type.
///
/// If there are no more arguments or the type is wrong,
/// this will return an error.
pub fn get_pos<T>(&mut self) -> ParseResult<Spanned<T::Output>> where T: Argument<'a> {
self.get_pos_opt::<T>()?
.ok_or_else(|| perr!(@"expected {}", T::ERROR_MESSAGE))
}
/// Get the next positional argument if there is any.
///
/// If the argument is of the wrong type, this will return an error.
pub fn get_pos_opt<T>(&mut self) -> ParseResult<Option<Spanned<T::Output>>>
where T: Argument<'a> {
let arg = self.args.positional
.get(self.positional_index)
.map(T::from_expr)
.transpose();
if let Ok(Some(_)) = arg {
self.positional_index += 1;
}
arg
}
/// Get a keyword argument with the given key and type.
pub fn get_key<T>(&mut self, key: &str) -> ParseResult<Spanned<T::Output>>
where T: Argument<'a> {
self.get_key_opt::<T>(key)?
.ok_or_else(|| perr!(@"expected {}", T::ERROR_MESSAGE))
}
/// Get a keyword argument with the given key and type if it is present.
pub fn get_key_opt<T>(&mut self, key: &str) -> ParseResult<Option<Spanned<T::Output>>>
where T: Argument<'a> {
self.args.keyword.iter()
.find(|entry| entry.val.0.val == key)
.map(|entry| T::from_expr(&entry.val.1))
.transpose()
}
/// Assert that there are no positional arguments left. Returns an error, otherwise.
pub fn done(&self) -> ParseResult<()> {
if self.positional_index == self.args.positional.len() {
Ok(())
} else {
perr!("unexpected argument");
}
}
}
/// A kind of argument.
pub trait Argument<'a> {
type Output;
const ERROR_MESSAGE: &'static str;
fn from_expr(expr: &'a Spanned<Expression>) -> ParseResult<Spanned<Self::Output>>;
}
macro_rules! arg {
($type:ident, $err:expr, $doc:expr, $output:ty, $wanted:pat => $converted:expr) => (
#[doc = $doc]
#[doc = " argument for use with the [`ArgParser`]."]
pub struct $type;
impl<'a> Argument<'a> for $type {
type Output = $output;
const ERROR_MESSAGE: &'static str = $err;
fn from_expr(expr: &'a Spanned<Expression>) -> ParseResult<Spanned<Self::Output>> {
#[allow(unreachable_patterns)]
match &expr.val {
$wanted => Ok(Spanned::new($converted, expr.span)),
_ => perr!("expected {}", $err),
}
}
}
);
}
arg!(ArgExpr, "expression", "A generic expression", &'a Expression, expr => &expr);
arg!(ArgIdent, "identifier", "An identifier (e.g. `horizontal`)", &'a str, Ident(s) => s.as_str());
arg!(ArgStr, "string", "A string (e.g. `\"Hello\"`)", &'a str, Str(s) => s.as_str());
arg!(ArgNum, "number", "A number (e.g. `5.4`)", f64, Num(n) => *n);
arg!(ArgSize, "size", "A size (e.g. `12pt`)", crate::size::Size, Size(s) => *s);
arg!(ArgBool, "bool", "A boolean (`true` or `false`)", bool, Bool(b) => *b);
|
