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//! The Value enum, a dynamically typed way of representing any valid S-expression value. //! //! # Constructing S-Expressions //! //! Lexpr provides a [`sexp!` macro][macro] to build `lexpr::Value` //! objects with very natural S-expression syntax. //! //! ``` //! use lexpr::sexp; //! //! // The type of `john` is `lexpr::Value` //! let john = sexp!(( //! (name . "John Doe") //! (age . 43) //! (phones "+44 1234567" "+44 2345678") //! )); //! //! println!("first phone number: {}", john["phones"][0]); //! //! // Convert to a string of S-expression data and print it out //! println!("{}", john.to_string()); //! ``` //! //! The `Value::to_string()` function converts a `lexpr::Value` into a //! `String` of S-expression text. //! //! One neat thing about the `sexp!` macro is that variables and //! expressions can be interpolated directly into the S-expression //! value as you are building it. The macro will check at compile time //! that the value you are interpolating is able to be represented as //! S-expression data. //! //! To interpolate, use the comma (`,`, also known as "unqote" in //! Lisp). The interpolated expression must either be a single token, //! or surrounded by round or curly braces. //! //! ``` //! # use lexpr::sexp; //! # //! # fn random_phone() -> u16 { 0 } //! # //! let full_name = "John Doe"; //! let age_last_year = 42; //! //! // The type of `john` is `lexpr::Value` //! let john = sexp!(( //! (name . ,full_name) //! (age . ,(age_last_year + 1)) //! (phones ,{ format!("+44 {}", random_phone()) }) //! )); //! ``` //! //! A string of S-expression data can be parsed into a `lexpr::Value` by the //! [`lexpr::from_str`][from_str] function. There is also //! [`from_slice`][from_slice] for parsing from a byte slice `&[u8]` and //! [`from_reader`][from_reader] for parsing from any `io::Read` like a file or //! a TCP stream. For all these functions there also is a `_custom` variant //! which allows for specifying parser options, in case the input deviates from //! the `lexpr` default behavior. //! //! ``` //! use lexpr::{sexp, parse::Error, Value}; //! //! # fn main() -> Result<(), Error> { //! // Some S-expression input data as a &str. Maybe this comes from the user. //! let data = r#"( //! (name . "John Doe") //! (age . 43) //! (phones . ( //! "+44 1234567" //! "+44 2345678" //! )) //! )"#; //! //! // Parse the string of data into lexpr::Value. //! let v: Value = lexpr::from_str(data)?; //! //! // Access parts of the data by indexing with square brackets. //! println!("Please call {} at the number {}", v["name"], v["phones"][0]); //! # Ok(()) //! # } //! ``` //! //! [macro]: ../macro.sexp.html //! [from_str]: ../parse/fn.from_str.html //! [from_slice]: ../parse/fn.from_slice.html //! [from_reader]: ../parse/fn.from_reader.html use std::fmt; use std::io; use std::str; use crate::cons::{self, Cons}; use crate::number::Number; pub use self::index::Index; /// Represents an S-expression value. /// /// See the [`lexpr::value`] module documentation for usage examples. /// /// [`lexpr::value`]: index.html #[derive(Debug, PartialEq, Clone)] pub enum Value { /// The special "nil" value. /// /// This is kind of an oddball value. In traditional Lisps (e.g., Common /// Lisp or Emacs Lisp) the empty list can be written as the symbol `nil`, /// while in Scheme, `nil` is just a regular symbol. Furthermore, /// traditional Lisps don't have a separate boolean data type, and represent /// true and false by the symbols `t` and `nil` instead. The `lexpr` parser /// can be instructed to parse the `nil` symbol as the `Nil` value (see /// [`NilSymbol::Special`]), allowing to choose its representation when /// converting to text again (see [`NilSyntax`]). Note that the empty list, /// when written as `()` or implicitly constructed as a list terminator, is /// always parsed as [`Value::Null`], not `Value::Nil`. /// /// In addition to being useful for conversions between S-expression /// variants, this value is also potentially returned when using the square /// bracket indexing operator on `Value`. /// /// [`NilSymbol::Special`]: crate::parse::NilSymbol::Special /// [`NilSyntax`]: ../print/enum.NilSyntax.html Nil, /// The empty list. /// /// This value terminates a chain of cons cells forming a proper list. Null, /// A boolean value. Bool(bool), /// A number. Number(Number), /// A character. Char(char), /// A string. String(Box<str>), /// A symbol. Symbol(Box<str>), /// A keyword. Keyword(Box<str>), /// A byte vector. Bytes(Box<[u8]>), /// Represents a Lisp "cons cell". /// /// Cons cells are often used to form singly-linked lists. /// ``` /// # use lexpr::sexp; /// let v = sexp!((a list 1 2 3)); /// assert!(v.is_cons()); /// assert_eq!(v[4], sexp!(3)); /// ``` Cons(Cons), /// A Lisp vector. Vector(Box<[Value]>), } impl Value { /// Construct a symbol, given its name. pub fn symbol(name: impl Into<Box<str>>) -> Self { Value::Symbol(name.into()) } /// Construct a keyword, given its name. /// /// ``` /// # use lexpr::Value; /// let value = Value::keyword("foo"); /// assert!(value.is_keyword()); /// assert_eq!(value.as_keyword().unwrap(), "foo"); /// ``` pub fn keyword(name: impl Into<Box<str>>) -> Self { Value::Keyword(name.into()) } /// Construct a string. /// /// ``` /// # use lexpr::Value; /// let value = Value::string("foo"); /// assert!(value.is_string()); /// assert_eq!(value.as_str().unwrap(), "foo"); /// ``` pub fn string(s: impl Into<Box<str>>) -> Self { Value::String(s.into()) } /// Construct a byte vector. /// /// ``` /// # use lexpr::Value; /// let value = Value::bytes(b"foo" as &[u8]); /// assert!(value.is_bytes()); /// assert_eq!(value.as_bytes().unwrap(), b"foo"); /// ``` pub fn bytes(bv: impl Into<Box<[u8]>>) -> Self { Value::Bytes(bv.into()) } /// Create a cons cell given its `car` and `cdr` fields. /// /// ``` /// # use lexpr::Value; /// let value = Value::cons(1, Value::Null); /// assert!(value.is_cons()); /// assert_eq!(value.as_pair().unwrap(), (&Value::from(1), &Value::Null)); /// ``` /// /// Note that you can also construct a cons cell from a Rust pair via the /// `From` trait: /// /// ``` /// # use lexpr::Value; /// let value = Value::from((42, "answer")); /// assert!(value.is_cons()); /// assert_eq!(value.as_pair().unwrap(), (&Value::from(42), &Value::string("answer"))); /// ``` pub fn cons<T, U>(car: T, cdr: U) -> Self where T: Into<Value>, U: Into<Value>, { Value::Cons(Cons::new(car, cdr)) } /// Create a list value from elements convertible into `Value`. /// /// ``` /// # use lexpr::{sexp, Value}; /// assert_eq!(Value::list(vec![1, 2, 3]), sexp!((1 2 3))); /// ``` pub fn list<I>(elements: I) -> Self where I: IntoIterator, I::Item: Into<Value>, { Self::append(elements, Value::Null) } /// Returns true if the value is a (proper) list. pub fn is_list(&self) -> bool { match self { Value::Null => true, Value::Cons(pair) => pair.iter().all(|p| match p.cdr() { Value::Null | Value::Cons(_) => true, _ => false, }), _ => false, } } /// Returns true if the value is a dotted (improper) list. /// /// Note that all values that are not pairs are considered dotted lists. /// /// ``` /// # use lexpr::{sexp, Value}; /// let list = sexp!((1 2 3)); /// assert!(!list.is_dotted_list()); /// let dotted = sexp!((1 2 . 3)); /// assert!(dotted.is_dotted_list()); /// ``` pub fn is_dotted_list(&self) -> bool { match self { Value::Null => false, Value::Cons(pair) => pair.iter().all(|p| match p.cdr() { Value::Null => false, _ => true, }), _ => true, } } /// Create a list value from elements convertible into `Value`, using a /// given value as a tail. /// /// ``` /// # use lexpr::{sexp, Value}; /// assert_eq!(Value::append(vec![1u32, 2], 3), sexp!((1 2 . 3))); /// assert_eq!(Value::append(vec![1u32, 2, 3], sexp!((4 5))), sexp!((1 2 3 4 5))); /// ``` pub fn append<I, T>(elements: I, tail: T) -> Self where I: IntoIterator, I::Item: Into<Value>, T: Into<Value>, { let mut list = Cons::new(Value::Nil, Value::Null); let mut pair = &mut list; let mut have_value = false; for item in elements { if have_value { pair.set_cdr(Value::from((Value::Nil, Value::Null))); pair = pair.cdr_mut().as_cons_mut().unwrap(); } pair.set_car(item.into()); have_value = true; } if have_value { pair.set_cdr(tail.into()); Value::Cons(list) } else { tail.into() } } /// Create a vector value from elements convertible into `Value`. /// /// ``` /// # use lexpr::{sexp, Value}; /// assert_eq!(Value::vector(vec![1u32, 2, 3]), sexp!(#(1 2 3))); /// ``` pub fn vector<I>(elements: I) -> Self where I: IntoIterator, I::Item: Into<Value>, { let v: Vec<_> = elements.into_iter().map(Into::into).collect(); Value::Vector(v.into_boxed_slice()) } /// Returns true if the value is a String. Returns false otherwise. /// /// For any Value on which `is_string` returns true, `as_str` is guaranteed /// to return the string slice. /// /// ``` /// # use lexpr::sexp; /// # /// let v = sexp!(((a . "some string") (b . #f))); /// /// assert!(v["a"].is_string()); /// /// // The boolean `false` is not a string. /// assert!(!v["b"].is_string()); /// ``` pub fn is_string(&self) -> bool { self.as_str().is_some() } /// If the value is a String, returns the associated str. Returns `None` /// otherwise. /// /// ``` /// # use lexpr::sexp; /// # /// let v = sexp!(((a . "some string") (b . #f))); /// /// assert_eq!(v["a"].as_str(), Some("some string")); /// /// // The boolean `false` is not a string. /// assert_eq!(v["b"].as_str(), None); /// /// // S-expression values are printed in S-expression /// // representation, so strings are in quotes. /// // The value is: "some string" /// println!("The value is: {}", v["a"]); /// /// // Rust strings are printed without quotes. /// // /// // The value is: some string /// println!("The value is: {}", v["a"].as_str().unwrap()); /// ``` pub fn as_str(&self) -> Option<&str> { match self { Value::String(s) => Some(s), _ => None, } } /// Returns true if the value is a symbol. Returns false otherwise. /// /// For any Value on which `is_symbol` returns true, `as_symbol` is guaranteed /// to return the string slice. /// /// ``` /// # use lexpr::sexp; /// # /// let v = sexp!((#:foo bar "baz")); /// /// assert!(v[1].is_symbol()); /// /// // Keywords and strings are not symbols. /// assert!(!v[0].is_symbol()); /// assert!(!v[2].is_symbol()); /// ``` pub fn is_symbol(&self) -> bool { self.as_symbol().is_some() } /// If the value is a symbol, returns the associated str. Returns `None` /// otherwise. /// /// ``` /// # use lexpr::sexp; /// # /// let v = sexp!(foo); /// /// assert_eq!(v.as_symbol(), Some("foo")); /// ``` pub fn as_symbol(&self) -> Option<&str> { match self { Value::Symbol(s) => Some(s), _ => None, } } /// Returns true if the value is a keyword. Returns false otherwise. /// /// For any Value on which `is_keyword` returns true, `as_keyword` is guaranteed /// to return the string slice. /// /// ``` /// # use lexpr::sexp; /// # /// let v = sexp!((#:foo bar "baz")); /// /// assert!(v[0].is_keyword()); /// /// // Symbols and strings are not keywords. /// assert!(!v[1].is_keyword()); /// assert!(!v[2].is_keyword()); /// ``` pub fn is_keyword(&self) -> bool { self.as_keyword().is_some() } /// If the value is a keyword, returns the associated str. Returns `None` /// otherwise. /// /// ``` /// # use lexpr::sexp; /// # /// let v = sexp!(#:foo); /// /// assert_eq!(v.as_keyword(), Some("foo")); /// ``` pub fn as_keyword(&self) -> Option<&str> { match self { Value::Keyword(s) => Some(s), _ => None, } } /// Get the name of a symbol or keyword, or the value of a string. /// /// This is useful if symbols, keywords and strings need to be treated /// equivalently in some context. /// /// ``` /// # use lexpr::sexp; /// # /// let kw = sexp!(#:foo); /// assert_eq!(kw.as_name(), Some("foo")); /// /// let sym = sexp!(bar); /// assert_eq!(sym.as_name(), Some("bar")); /// /// let s = sexp!("baz"); /// assert_eq!(s.as_name(), Some("baz")); /// ``` pub fn as_name(&self) -> Option<&str> { match self { Value::Symbol(s) => Some(s), Value::Keyword(s) => Some(s), Value::String(s) => Some(s), _ => None, } } /// Returns true if the value is a byte vector. Returns false otherwise. /// /// For any Value on which `is_bytes` returns true, `as_bytes` is guaranteed /// to return the byte slice. /// /// ``` /// # use lexpr::sexp; /// # /// let v = sexp!(((a . ,(b"some bytes" as &[u8])) (b . "string"))); /// /// assert!(v["a"].is_bytes()); /// /// // A string is not a byte vector. /// assert!(!v["b"].is_bytes()); /// ``` pub fn is_bytes(&self) -> bool { self.as_bytes().is_some() } /// If the value is a byte vector, returns the associated byte /// slice. Returns `None` otherwise. /// /// ``` /// # use lexpr::sexp; /// # /// let v = sexp!(((a . ,(b"some bytes" as &[u8])) (b . "string"))); /// /// assert_eq!(v["a"].as_bytes(), Some(b"some bytes" as &[u8])); /// /// // A string is not a byte vector. /// assert_eq!(v["b"].as_bytes(), None); /// ``` pub fn as_bytes(&self) -> Option<&[u8]> { match self { Value::Bytes(s) => Some(s), _ => None, } } /// Return `true` if the value is a number. pub fn is_number(&self) -> bool { self.as_number().is_some() } /// For numbers, return a reference to them. For other values, return /// `None`. pub fn as_number(&self) -> Option<&Number> { match self { Value::Number(n) => Some(n), _ => None, } } /// Returns true if the value is an integer between `i64::MIN` and /// `i64::MAX`. /// /// For any Value on which `is_i64` returns true, `as_i64` is guaranteed to /// return the integer value. /// /// ``` /// # use lexpr::sexp; /// # /// let big = i64::max_value() as u64 + 10; /// let v = sexp!(((a . 64) (b . ,big) (c . 256.0))); /// /// assert!(v["a"].is_i64()); /// /// // Greater than i64::MAX. /// assert!(!v["b"].is_i64()); /// /// // Numbers with a decimal point are not considered integers. /// assert!(!v["c"].is_i64()); /// ``` pub fn is_i64(&self) -> bool { match self.as_number() { Some(n) => n.is_i64(), _ => false, } } /// Returns true if the value is an integer between zero and `u64::MAX`. /// /// For any Value on which `is_u64` returns true, `as_u64` is guaranteed to /// return the integer value. /// /// ``` /// # use lexpr::sexp; /// # /// let v = sexp!(((a . 64) (b . -64) (c . 256.0))); /// /// assert!(v["a"].is_u64()); /// /// // Negative integer. /// assert!(!v["b"].is_u64()); /// /// // Numbers with a decimal point are not considered integers. /// assert!(!v["c"].is_u64()); /// ``` pub fn is_u64(&self) -> bool { match self.as_number() { Some(n) => n.is_u64(), _ => false, } } /// Returns true if the value is a number that can be represented by f64. /// /// For any Value on which `is_f64` returns true, `as_f64` is guaranteed to /// return the floating point value. /// /// Currently this function returns true if and only if both `is_i64` and /// `is_u64` return false but this is not a guarantee in the future. /// /// ``` /// # use lexpr::sexp; /// # /// let v = sexp!(((a . 256.0) (b . 64) (c . -64))); /// /// assert!(v["a"].is_f64()); /// /// // Integers. /// assert!(!v["b"].is_f64()); /// assert!(!v["c"].is_f64()); /// ``` #[inline] pub fn is_f64(&self) -> bool { match self.as_number() { Some(n) => n.is_f64(), _ => false, } } /// If the value is an integer, represent it as i64 if possible. Returns /// None otherwise. /// /// ``` /// # use lexpr::sexp; /// # /// let big = i64::max_value() as u64 + 10; /// let v = sexp!(((a . 64) (b . ,big) (c . 256.0))); /// /// assert_eq!(v["a"].as_i64(), Some(64)); /// assert_eq!(v["b"].as_i64(), None); /// assert_eq!(v["c"].as_i64(), None); /// ``` #[inline] pub fn as_i64(&self) -> Option<i64> { self.as_number().and_then(Number::as_i64) } /// If the value is an integer, represent it as u64 if possible. Returns /// None otherwise. /// /// ``` /// # use lexpr::sexp; /// # /// let v = sexp!(((a . 64) (b . -64) (c . 256.0))); /// /// assert_eq!(v["a"].as_u64(), Some(64)); /// assert_eq!(v["b"].as_u64(), None); /// assert_eq!(v["c"].as_u64(), None); /// ``` pub fn as_u64(&self) -> Option<u64> { self.as_number().and_then(Number::as_u64) } /// If the value is a number, represent it as f64 if possible. Returns /// None otherwise. /// /// ``` /// # use lexpr::sexp; /// # /// let v = sexp!(((a . 256.0) (b . 64) (c . -64))); /// /// assert_eq!(v["a"].as_f64(), Some(256.0)); /// assert_eq!(v["b"].as_f64(), Some(64.0)); /// assert_eq!(v["c"].as_f64(), Some(-64.0)); /// ``` pub fn as_f64(&self) -> Option<f64> { self.as_number().and_then(Number::as_f64) } /// Returns true if the value is a Boolean. Returns false otherwise. /// /// For any Value on which `is_boolean` returns true, `as_bool` is /// guaranteed to return the boolean value. /// /// ``` /// # use lexpr::sexp; /// # /// let v = sexp!(((a . #f) (b . #nil))); /// /// assert!(v["a"].is_boolean()); /// /// // The nil value is special, and not a boolean. /// assert!(!v["b"].is_boolean()); /// ``` pub fn is_boolean(&self) -> bool { self.as_bool().is_some() } /// If the value is a `Boolean`, returns the associated bool. Returns None /// otherwise. /// /// ``` /// # use lexpr::sexp; /// # /// let v = sexp!(((a . #f) (b . "false"))); /// /// assert_eq!(v["a"].as_bool(), Some(false)); /// /// // The string `"false"` is a string, not a boolean. /// assert_eq!(v["b"].as_bool(), None); /// ``` pub fn as_bool(&self) -> Option<bool> { match self { Value::Bool(b) => Some(*b), _ => None, } } /// Returns true if the value is a character. Returns false otherwise. pub fn is_char(&self) -> bool { self.as_char().is_some() } /// If the value is a character, returns the associated `char`. Returns None /// otherwise. /// /// ``` /// # use lexpr::sexp; /// # /// let v = sexp!(((a . 'c') (b . "c"))); /// /// assert_eq!(v["a"].as_char(), Some('c')); /// /// // The string `"c"` is a single-character string, not a character. /// assert_eq!(v["b"].as_char(), None); /// ``` pub fn as_char(&self) -> Option<char> { match self { Value::Char(c) => Some(*c), _ => None, } } /// Returns true if the value is `Nil`. Returns false otherwise. /// /// For any Value on which `is_nil` returns true, `as_nil` is guaranteed /// to return `Some(())`. /// /// ``` /// # use lexpr::sexp; /// # /// let v = sexp!(((a . #nil) (b . #f))); /// /// assert!(v["a"].is_nil()); /// /// // The boolean `false` is not nil. /// assert!(!v["b"].is_nil()); /// ``` pub fn is_nil(&self) -> bool { self.as_nil().is_some() } /// If the value is `Nil`, returns `()`. Returns `None` otherwise. /// /// ``` /// # use lexpr::sexp; /// # /// let v = sexp!(((a . #nil) (b . #f) (c . ()))); /// /// assert_eq!(v["a"].as_nil(), Some(())); /// /// // The boolean `false` is not nil. /// assert_eq!(v["b"].as_nil(), None); /// // Neither is the empty list. /// assert_eq!(v["c"].as_nil(), None); /// ``` pub fn as_nil(&self) -> Option<()> { match self { Value::Nil => Some(()), _ => None, } } /// Returns true if the value is `Null`. Returns false otherwise. pub fn is_null(&self) -> bool { self.as_null().is_some() } /// If the value is `Null`, returns `()`. Returns `None` otherwise. pub fn as_null(&self) -> Option<()> { match self { Value::Null => Some(()), _ => None, } } /// Returns true if the value is a cons cell. Returns `False` otherwise. pub fn is_cons(&self) -> bool { match self { Value::Cons(_) => true, _ => false, } } /// If the value is a cons cell, returns a reference to it. Returns `None` /// otherwise. pub fn as_cons(&self) -> Option<&Cons> { match self { Value::Cons(pair) => Some(pair), _ => None, } } /// If the value is a cons cell, returns a mutable reference to it. Returns /// `None` otherwise. pub fn as_cons_mut(&mut self) -> Option<&mut Cons> { match self { Value::Cons(pair) => Some(pair), _ => None, } } /// If the value is a cons cell, return references to its `car` and `cdr` /// fields. /// /// ``` /// # use lexpr::sexp; /// let cell = sexp!((foo . bar)); /// assert_eq!(cell.as_pair(), Some((&sexp!(foo), &sexp!(bar)))); /// assert_eq!(sexp!("not-a-pair").as_pair(), None); /// ``` pub fn as_pair(&self) -> Option<(&Value, &Value)> { self.as_cons().map(Cons::as_pair) } /// Returns true if the value is a vector. pub fn is_vector(&self) -> bool { match self { Value::Vector(_) => true, _ => false, } } /// If the value is a vector, return a reference to its elements. /// /// ``` /// # use lexpr::{sexp, Value}; /// let v = sexp!(#(1 2 "three")); /// let slice: &[Value] = &[sexp!(1), sexp!(2), sexp!("three")]; /// assert_eq!(v.as_slice(), Some(slice)); /// ``` pub fn as_slice(&self) -> Option<&[Value]> { match self { Value::Vector(elements) => Some(elements), _ => None, } } /// If the value is a vector, return a mutable reference to its elements. /// /// ``` /// # use lexpr::{sexp, Value}; /// let mut v = sexp!(#(1 2 "three")); /// v.as_slice_mut().unwrap()[2] = sexp!(3); /// let slice: &[Value] = &[sexp!(1), sexp!(2), sexp!(3)]; /// assert_eq!(v.as_slice(), Some(slice)); /// ``` pub fn as_slice_mut(&mut self) -> Option<&mut [Value]> { match self { Value::Vector(elements) => Some(elements), _ => None, } } /// If the value is a list, return an iterator over the list elements. /// /// If the value 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 value = lexpr::from_str("(1 2 . 3)").unwrap(); /// let mut iter = value.list_iter().unwrap(); /// assert_eq!(iter.next(), Some(&sexp!(1))); /// assert_eq!(iter.next(), Some(&sexp!(2))); /// assert_eq!(iter.next(), None); /// assert_eq!(iter.next(), Some(&sexp!(3))); /// assert_eq!(iter.next(), None); /// ``` pub fn list_iter(&self) -> Option<cons::ListIter<'_>> { match self { Value::Cons(cell) => Some(cons::ListIter::cons(cell)), Value::Null => Some(cons::ListIter::empty()), _ => None, } } /// Attempts conversion to a vector, cloning the values. /// /// For proper lists (including `Value::Null`), this returns a vector of /// values. If you want to handle improper list in a similar way, combine /// [`as_cons`] and the [`Cons::to_vec`] method. /// /// ``` /// # use lexpr::{sexp, Value}; /// assert_eq!(sexp!((1 2 3)).to_vec(), Some(vec![sexp!(1), sexp!(2), sexp!(3)])); /// assert_eq!(sexp!(()).to_vec(), Some(vec![])); /// assert_eq!(sexp!((1 2 . 3)).to_vec(), None); /// ``` /// [`as_cons`]: Value::as_cons pub fn to_vec(&self) -> Option<Vec<Value>> { match self { Value::Null => Some(Vec::new()), Value::Cons(pair) => { let (vec, rest) = pair.to_ref_vec(); if rest.is_null() { Some(vec.into_iter().cloned().collect()) } else { None } } _ => None, } } /// Attempts conversion to a vector, taking references to the values. /// /// For proper lists (including `Value::Null`), this returns a vector of /// value references. If you want to handle improper list in a similar way, /// combine [`as_cons`] and the [`Cons::to_ref_vec`] method. /// /// ``` /// # use lexpr::{sexp, Value}; /// assert_eq!(sexp!((1 2 3)).to_ref_vec(), Some(vec![&sexp!(1), &sexp!(2), &sexp!(3)])); /// assert_eq!(sexp!(()).to_ref_vec(), Some(vec![])); /// assert_eq!(sexp!((1 2 . 3)).to_ref_vec(), None); /// ``` /// /// [`as_cons`]: Value::as_cons pub fn to_ref_vec(&self) -> Option<Vec<&Value>> { match self { Value::Null => Some(Vec::new()), Value::Cons(pair) => { let (vec, rest) = pair.to_ref_vec(); if rest.is_null() { Some(vec) } else { None } } _ => None, } } /// Index into a S-expression list. A string or `Value` value can /// be used to access a value in an association list, and a usize /// index can be used to access the n-th element of a list. /// /// For indexing into association lists, the given string will /// match strings, symbols and keywords. /// /// Returns `None` if the type of `self` does not match the type /// of the index, for example if the index is a string and `self` /// is not an association list. Also returns `None` if the given /// key does not exist in the map or the given index is not within /// the bounds of the list; note that the tail of an improper list /// is also considered out-of-bounds. /// /// In Scheme terms, this method can be thought of a combination /// of `assoc-ref` and `list-ref`, depending on the argument type. If /// you want to look up a number in an association list, use an /// `Value` value containing that number. /// /// ``` /// # use lexpr::sexp; /// # /// let alist = sexp!((("A" . 65) (B . 66) (#:C . 67) (42 . "The answer"))); /// assert_eq!(alist.get("A").unwrap(), &sexp!(65)); /// assert_eq!(alist.get("B").unwrap(), &sexp!(66)); /// assert_eq!(alist.get("C").unwrap(), &sexp!(67)); /// assert_eq!(alist.get(sexp!(42)).unwrap(), &sexp!("The answer")); /// /// let list = sexp!(("A" "B" "C")); /// assert_eq!(*list.get(2).unwrap(), sexp!("C")); /// /// assert_eq!(list.get("A"), None); /// ``` /// /// Square brackets can also be used to index into a value in a /// more concise way. This returns the nil value in cases where /// `get` would have returned `None`. See [`Index`] for details. /// /// ``` /// # use lexpr::sexp; /// # /// let alist = sexp!(( /// ("A" . ("a" "á" "à")) /// ("B" . ((b . 42) (c . 23))) /// ("C" . ("c" "ć" "ć̣" "ḉ")) /// )); /// assert_eq!(alist["B"][0], sexp!((b . 42))); /// assert_eq!(alist["C"][1], sexp!("ć")); /// /// assert_eq!(alist["D"], sexp!(#nil)); /// assert_eq!(alist[0]["x"]["y"]["z"], sexp!(#nil)); /// ``` /// /// [`Index`]: trait.Index.html pub fn get<I: Index>(&self, index: I) -> Option<&Value> { index.index_into(self) } } struct WriterFormatter<'a, 'b> { inner: &'a mut fmt::Formatter<'b>, } impl<'a, 'b> io::Write for WriterFormatter<'a, 'b> { fn write(&mut self, buf: &[u8]) -> io::Result<usize> { fn io_error<E>(_: E) -> io::Error { // Sexp does not matter because fmt::Debug and fmt::Display impls // below just map it to fmt::Error io::Error::new(io::ErrorKind::Other, "fmt error") } let s = str::from_utf8(buf).map_err(io_error)?; self.inner.write_str(s).map_err(io_error)?; Ok(buf.len()) } fn flush(&mut self) -> io::Result<()> { Ok(()) } } impl fmt::Display for Value { /// Display an S-expression value as a string. /// /// ``` /// # use lexpr::sexp; /// # /// let value = sexp!(((city "London") (street "10 Downing Street"))); /// /// // Compact format: /// // /// // ((city "London") (street "10 Downing Street")) /// let compact = format!("{}", value); /// assert_eq!(compact, /// r#"((city "London") (street "10 Downing Street"))"#); /// ``` fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { let mut wr = WriterFormatter { inner: f }; crate::print::to_writer(&mut wr, self).map_err(|_| fmt::Error) } } impl str::FromStr for Value { /// Parse an S-expression value from a string. type Err = crate::parse::Error; fn from_str(s: &str) -> Result<Self, Self::Err> { crate::parse::from_str(s) } } mod from; mod index; mod partial_eq; #[cfg(test)] mod tests;