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use std::fmt::{self, Debug, Formatter};
use std::ops::Deref;
use std::rc::Rc;
use super::{Cast, EvalContext, Value};
use crate::diag::{At, TypResult};
use crate::syntax::{Span, Spanned};
use crate::util::EcoString;
/// An evaluatable function.
#[derive(Clone)]
pub struct Function(Rc<Repr<Func>>);
/// The unsized representation behind the [`Rc`].
struct Repr<T: ?Sized> {
name: Option<EcoString>,
func: T,
}
type Func = dyn Fn(&mut EvalContext, &mut FuncArgs) -> TypResult<Value>;
impl Function {
/// Create a new function from a rust closure.
pub fn new<F>(name: Option<EcoString>, func: F) -> Self
where
F: Fn(&mut EvalContext, &mut FuncArgs) -> TypResult<Value> + 'static,
{
Self(Rc::new(Repr { name, func }))
}
/// The name of the function.
pub fn name(&self) -> Option<&EcoString> {
self.0.name.as_ref()
}
}
impl Deref for Function {
type Target = Func;
fn deref(&self) -> &Self::Target {
&self.0.func
}
}
impl Debug for Function {
fn fmt(&self, f: &mut Formatter) -> fmt::Result {
f.debug_struct("ValueFunc").field("name", &self.0.name).finish()
}
}
impl PartialEq for Function {
fn eq(&self, other: &Self) -> bool {
// We cast to thin pointers for comparison.
Rc::as_ptr(&self.0) as *const () == Rc::as_ptr(&other.0) as *const ()
}
}
/// Evaluated arguments to a function.
#[derive(Debug, Clone, PartialEq)]
pub struct FuncArgs {
/// The span of the whole argument list.
pub span: Span,
/// The positional arguments.
pub items: Vec<FuncArg>,
}
/// An argument to a function call: `12` or `draw: false`.
#[derive(Debug, Clone, PartialEq)]
pub struct FuncArg {
/// The span of the whole argument.
pub span: Span,
/// The name of the argument (`None` for positional arguments).
pub name: Option<EcoString>,
/// The value of the argument.
pub value: Spanned<Value>,
}
impl FuncArgs {
/// Find and consume the first castable positional argument.
pub fn eat<T>(&mut self) -> Option<T>
where
T: Cast<Spanned<Value>>,
{
for (i, slot) in self.items.iter().enumerate() {
if slot.name.is_none() {
if T::is(&slot.value) {
let value = self.items.remove(i).value;
return T::cast(value).ok();
}
}
}
None
}
/// Find and consume the first castable positional argument, returning a
/// `missing argument: {what}` error if no match was found.
pub fn expect<T>(&mut self, what: &str) -> TypResult<T>
where
T: Cast<Spanned<Value>>,
{
match self.eat() {
Some(found) => Ok(found),
None => bail!(self.span, "missing argument: {}", what),
}
}
/// Find and consume all castable positional arguments.
pub fn all<T>(&mut self) -> impl Iterator<Item = T> + '_
where
T: Cast<Spanned<Value>>,
{
std::iter::from_fn(move || self.eat())
}
/// Cast and remove the value for the given named argument, returning an
/// error if the conversion fails.
pub fn named<T>(&mut self, name: &str) -> TypResult<Option<T>>
where
T: Cast<Spanned<Value>>,
{
let index = match self
.items
.iter()
.filter_map(|arg| arg.name.as_deref())
.position(|other| name == other)
{
Some(index) => index,
None => return Ok(None),
};
let value = self.items.remove(index).value;
let span = value.span;
T::cast(value).map(Some).at(span)
}
/// Return an "unexpected argument" error if there is any remaining
/// argument.
pub fn finish(self) -> TypResult<()> {
if let Some(arg) = self.items.first() {
bail!(arg.span, "unexpected argument");
}
Ok(())
}
}
impl FuncArgs {
/// Reinterpret these arguments as actually being an array index.
pub fn into_index(self) -> TypResult<i64> {
self.into_castable("index")
}
/// Reinterpret these arguments as actually being a dictionary key.
pub fn into_key(self) -> TypResult<EcoString> {
self.into_castable("key")
}
/// Reinterpret these arguments as actually being a single castable thing.
fn into_castable<T>(self, what: &str) -> TypResult<T>
where
T: Cast<Value>,
{
let mut iter = self.items.into_iter();
let value = match iter.next() {
Some(FuncArg { name: None, value, .. }) => value.v.cast().at(value.span)?,
None => {
bail!(self.span, "missing {}", what);
}
Some(FuncArg { name: Some(_), span, .. }) => {
bail!(span, "named pair is not allowed here");
}
};
if let Some(arg) = iter.next() {
bail!(arg.span, "only one {} is allowed", what);
}
Ok(value)
}
}
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