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//! S-expression values including source location. use std::{io, iter, slice}; use crate::{ parse::{read, Options, Parser, Position, Result}, Cons, Value, }; /// Combines an S-expression value with location information. /// /// A `Datum` keeps, along with a plain `Value`, information about the text /// location the value was parsed from. For compound values, such as lists and /// vectors, that includes information for all contained values, recursively. /// /// A `Datum` can be obtained by using the [`parse_datum`] and [`expect_datum`] /// methods on `Parser`. /// /// [`parse_datum`]: Parser::parse_datum /// [`expect_datum`]: Parser::expect_datum #[derive(Debug, Clone, PartialEq)] pub struct Datum { value: Value, info: SpanInfo, } impl Datum { pub(crate) fn into_inner(self) -> (Value, SpanInfo) { (self.value, self.info) } /// Returns a reference to the contained value. pub fn value(&self) -> &Value { &self.value } /// Returns the span for the compelete value. pub fn span(&self) -> Span { self.info.span() } /// Returns a reference to the datum. pub fn as_ref(&self) -> Ref<'_> { Ref { value: &self.value, info: &self.info, } } /// Returns an iterator over the elements of a list. /// /// If the value contained in the datum is not either a cons cell or `Null`, `None` is /// returned. /// /// Note that the returned iterator has special behavior for improper lists, yielding the /// element after the dot after returning `None` the first time. /// /// ``` /// use lexpr::sexp; /// /// let datum = lexpr::datum::from_str("(1 2 . 3)").unwrap(); /// let mut iter = datum.list_iter().unwrap(); /// let one = iter.next().unwrap(); /// assert_eq!(one.value(), &sexp!(1)); /// let two = iter.next().unwrap(); /// assert_eq!(two.value(), &sexp!(2)); /// assert_eq!(iter.next(), None); /// let three = iter.next().unwrap(); /// assert_eq!(three.value(), &sexp!(3)); /// assert_eq!(iter.next(), None); /// ``` pub fn list_iter(&self) -> Option<ListIter<'_>> { self.as_ref().list_iter() } /// Returns an iterator over the elements of a vector. /// /// If the value contained in the datum is not a vector, `None` is returned. pub fn vector_iter(&self) -> Option<VectorIter<'_>> { self.as_ref().vector_iter() } pub(crate) fn primitive(value: Value, start: Position, end: Position) -> Self { Datum { value, info: SpanInfo::Prim(Span { start, end }), } } pub(crate) fn vec( elements: Vec<Value>, element_info: Vec<SpanInfo>, start: Position, end: Position, ) -> Self { Datum { value: Value::Vector(elements.into()), info: SpanInfo::Vec(Span { start, end }, element_info), } } pub(crate) fn cons(cell: Cons, meta: [SpanInfo; 2], start: Position, end: Position) -> Self { Datum { value: Value::Cons(cell), info: SpanInfo::Cons(Span::new(start, end), Box::new(meta)), } } pub(crate) fn quotation(name: &str, quoted: Datum, quote_span: Span) -> Self { let (quoted_value, quoted_info) = quoted.into_inner(); let quoted_end = quoted_info.span().end(); let null_span = Span::new(quoted_end, quoted_end); Datum { value: Value::list(vec![Value::symbol(name), quoted_value]), info: SpanInfo::Cons( Span::new(quote_span.start(), quoted_end), Box::new([ SpanInfo::Prim(quote_span), SpanInfo::Cons( quoted_info.span(), Box::new([quoted_info, SpanInfo::Prim(null_span)]), ), ]), ), } } } impl From<Datum> for Value { fn from(datum: Datum) -> Self { datum.value } } /// A reference to a value and corresponding location information. /// /// A `Ref` is the generalized version of `&Datum`; it can not only refer a top-level, owned `Datum` /// value, but also to values recursively contained therein. #[derive(Debug, Clone, Copy, PartialEq)] pub struct Ref<'a> { value: &'a Value, info: &'a SpanInfo, } impl<'a> AsRef<Value> for Ref<'a> { fn as_ref(&self) -> &Value { &self.value } } impl<'a> From<Ref<'a>> for Datum { /// Turns a reference into an owned `Datum`, by cloning the referenced value and location /// information. fn from(r: Ref<'a>) -> Self { Datum { value: r.value.clone(), info: r.info.clone(), } } } impl<'a> Ref<'a> { fn new(value: &'a Value, info: &'a SpanInfo) -> Self { Ref { value, info } } /// Returns the span of the referenced value. pub fn span(&self) -> Span { self.info.span() } /// Returns a reference to the contained value. pub fn value(&self) -> &'a Value { self.value } /// If the value referenced is not either a cons cell or `Null`, `None` is returned. /// /// Note that the returned iterator has special behavior for improper lists, yielding the /// element after the dot after returning `None` the first time; see [`Datum::list_iter`] for an /// example. pub fn list_iter(&self) -> Option<ListIter<'a>> { match (self.value, self.info) { (Value::Cons(cell), SpanInfo::Cons(_, meta)) => Some(ListIter::cons(cell, meta)), (Value::Null, _) => Some(ListIter::empty()), _ => None, } } /// Returns an iterator over the elements of a vector. /// /// If the value referenced is not a vector, `None` is returned. pub fn vector_iter(&self) -> Option<VectorIter<'a>> { match (self.value, self.info) { (Value::Vector(elements), SpanInfo::Vec(_, element_meta)) => { Some(VectorIter(elements.iter().zip(element_meta))) } _ => None, } } /// Returns a pair of references to the fields of a cons cell. /// /// If the value referenced is not a cons cell, `None` is returned. pub fn as_pair(&self) -> Option<(Ref<'a>, Ref<'a>)> { let (car, cdr) = self.value.as_pair()?; match &self.info { SpanInfo::Cons(_, inner) if inner.len() == 2 => { Some((Ref::new(car, &inner[0]), Ref::new(cdr, &inner[1]))) } _ => unreachable!("badly shaped pair span information"), } } } impl<'a> std::ops::Deref for Ref<'a> { type Target = Value; fn deref(&self) -> &Self::Target { self.value } } /// The start and end for a span of text. #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)] pub struct Span { start: Position, end: Position, } impl Span { pub(crate) fn new(start: Position, end: Position) -> Self { Span { start, end } } pub(crate) fn empty() -> Self { Span { start: Position::new(0, 0), end: Position::new(0, 0), } } /// Get the starting line/column in the source file for this span. pub fn start(&self) -> Position { self.start } /// Get the ending line/column in the source file for this span. pub fn end(&self) -> Position { self.end } } #[derive(Debug, Clone, PartialEq)] pub(crate) enum SpanInfo { Prim(Span), Cons(Span, Box<[SpanInfo; 2]>), Vec(Span, Vec<SpanInfo>), } impl SpanInfo { fn span(&self) -> Span { match self { SpanInfo::Prim(span) => *span, SpanInfo::Cons(span, _) => *span, SpanInfo::Vec(span, _) => *span, } } pub(crate) fn cons_mut(&mut self) -> Option<&mut [SpanInfo; 2]> { match self { SpanInfo::Cons(_, info) => Some(info), _ => None, } } } /// An iterator over the elements #[derive(Debug, Clone)] pub struct VectorIter<'a>(iter::Zip<slice::Iter<'a, Value>, slice::Iter<'a, SpanInfo>>); impl<'a> Iterator for VectorIter<'a> { type Item = Ref<'a>; fn next(&mut self) -> Option<Self::Item> { self.0.next().map(|(value, info)| Ref { value, info }) } } /// An iterator yielding the `car` field of a chain of cons cells. /// /// # Improper lists /// /// Since in Lisp, lists can be "improper", i.e., terminated by a value other than `Null`, this /// iterator type takes advantage of the fact that Rust's iterators can produce multiple sequences /// of values, each terminated by `None`. For an improper list, the terminating value is produced /// after the sequence of elements, as a singleton element, again followed by `None`. /// /// For example, while the list `(1 2 3)` will produce the three expected `Some` values, followed by /// `None`, the list `(1 2 . 3)` will produce `Some` values for `1` and `2`, then a `None`, followed /// by a some value for `3`, and then the final `None`. #[derive(Debug, Clone)] pub struct ListIter<'a>(ListCursor<'a>); impl<'a> ListIter<'a> { /// Returns true when the iterator is completely exhausted. /// /// For an improper list, true will only be returned after the terminating value has been /// consumed. pub fn is_empty(&self) -> bool { match &self.0 { ListCursor::Exhausted => true, _ => false, } } /// Returns a peek at the value that would be returned by a call to `next`. /// /// For improper lists, this implies that after the last regular element, `None` will be /// returned, while `is_empty` still returns false at that point. pub fn peek(&self) -> Option<Ref<'_>> { match &self.0 { ListCursor::Cons(cell, info) => Some(Ref { value: cell.car(), info: &info[0], }), ListCursor::Dot(_, _) => None, ListCursor::Rest(value, info) => Some(Ref { value, info }), ListCursor::Exhausted => None, } } fn empty() -> Self { ListIter(ListCursor::Exhausted) } fn cons(cell: &'a Cons, meta: &'a [SpanInfo; 2]) -> Self { ListIter(ListCursor::Cons(cell, meta)) } } #[derive(Debug, Clone)] enum ListCursor<'a> { Cons(&'a Cons, &'a [SpanInfo; 2]), Dot(&'a Value, &'a SpanInfo), Rest(&'a Value, &'a SpanInfo), Exhausted, } impl<'a> Iterator for ListIter<'a> { type Item = Ref<'a>; fn next(&mut self) -> Option<Self::Item> { match self.0 { ListCursor::Cons(cell, [car_meta, cdr_meta]) => { let car = cell.car(); match cdr_meta { SpanInfo::Cons(_, next) => { let cell = cell .cdr() .as_cons() .expect("badly shaped list span information"); self.0 = ListCursor::Cons(cell, next); } SpanInfo::Prim(_) if cell.cdr().is_null() => { self.0 = ListCursor::Exhausted; } _ => { self.0 = ListCursor::Dot(cell.cdr(), cdr_meta); } } Some(Ref { value: car, info: car_meta, }) } ListCursor::Dot(value, info) => { self.0 = ListCursor::Rest(value, info); None } ListCursor::Rest(value, info) => { self.0 = ListCursor::Exhausted; Some(Ref { value, info }) } ListCursor::Exhausted => None, } } } fn from_trait<'de, R>(read: R, options: Options) -> Result<Datum> where R: read::Read<'de>, { let mut parser = Parser::with_options(read, options); let datum = parser.expect_datum()?; parser.expect_end()?; Ok(datum) } /// Parse a datum from an IO stream containing a single S-expression. /// /// The content of the IO stream is parsed directly from the stream /// without being buffered in memory. /// /// When reading from a source against which short reads are not efficient, such /// as a [`File`], you will want to apply your own buffering, e.g. using /// [`std::io::BufReader`]. /// /// ```no_run /// use std::error::Error; /// use std::fs::File; /// use std::io::BufReader; /// use std::path::Path; /// /// fn read_datum_from_file<P: AsRef<Path>>(path: P) -> Result<lexpr::Datum, Box<dyn Error>> { /// // Open the file in read-only mode with buffer. /// let file = File::open(path)?; /// let reader = BufReader::new(file); /// /// // Read an arbitrary S-expression, using parser options suitable for Emacs Lisp. /// let datum = lexpr::datum::from_reader_custom(reader, lexpr::parse::Options::elisp())?; /// /// // Return the datum. /// Ok(datum) /// } /// /// let datum = read_datum_from_file("test.el").unwrap(); /// println!("{:?}", datum); /// ``` /// /// [`File`]: https://doc.rust-lang.org/std/fs/struct.File.html /// [`BufReader`]: https://doc.rust-lang.org/std/io/struct.BufReader.html pub fn from_reader_custom(rdr: impl io::Read, options: Options) -> Result<Datum> { from_trait(read::IoRead::new(rdr), options) } /// Parse a datum from an IO stream of S-expressions, using the default parser /// options. /// /// See [`from_reader_custom`] for more information. /// /// [`from_reader_custom`]: fn.from_reader_custom.html pub fn from_reader(rdr: impl io::Read) -> Result<Datum> { from_reader_custom(rdr, Options::default()) } /// Parse a datum from an IO stream of S-expressions, using the parser /// options suitable for parsing Emacs Lisp. /// /// See [`from_reader_custom`] for more information. /// /// [`from_reader_custom`]: fn.from_reader_custom.html pub fn from_reader_elisp(rdr: impl io::Read) -> Result<Datum> { from_reader_custom(rdr, Options::elisp()) } /// Parse a datum from bytes representing a single S-expression. /// /// ``` /// let datum = lexpr::from_slice_custom(b"(a (nested) list)", lexpr::parse::Options::new()); /// println!("{:?}", datum); /// ``` pub fn from_slice_custom(bytes: &[u8], options: Options) -> Result<Datum> { // TODO: the use of SliceRead is most probably not a good idea, since it calculates position // information on-demand, leading to O(n^2) complexity. from_trait(read::SliceRead::new(bytes), options) } /// Parse a datum from bytes representing a single S-expressions, using the /// default parser options. /// /// See [`from_slice_custom`] for more information. /// /// [`from_slice_custom`]: fn.from_slice_custom.html pub fn from_slice(bytes: &[u8]) -> Result<Datum> { from_slice_custom(bytes, Options::default()) } /// Parse a datum from bytes representing a single S-expressions, using parser /// options suitable for Emacs Lisp. /// /// See [`from_slice_custom`] for more information. /// /// [`from_slice_custom`]: fn.from_slice_custom.html pub fn from_slice_elisp(bytes: &[u8]) -> Result<Datum> { from_slice_custom(bytes, Options::elisp()) } /// Parse a datum from a string slice representing a single S-expression. /// /// ``` /// let datum = lexpr::from_str_custom("(a (nested) list)", lexpr::parse::Options::new()); /// println!("{:?}", datum); /// ``` pub fn from_str_custom(s: &str, options: Options) -> Result<Datum> { // TODO: the use of StrRead (which delegates to SliceRead) is most probably not a good idea, // since it calculates position information on-demand, leading to O(n^2) complexity. from_trait(read::StrRead::new(s), options) } /// Parse a datum from a string slice representing a single S-expressions, using /// the default parser options. /// /// See [`from_str_custom`] for more information. /// /// [`from_str_custom`]: fn.from_str_custom.html pub fn from_str(s: &str) -> Result<Datum> { from_str_custom(s, Options::default()) } /// Parse a datum from a string slice representing a single S-expression, using /// parser options suitable for Emacs Lisp. /// /// See [`from_str_custom`] for more information. /// /// [`from_str_custom`]: fn.from_str_custom.html pub fn from_str_elisp(s: &str) -> Result<Datum> { from_str_custom(s, Options::elisp()) }