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#![deny(missing_docs)] #![warn(rust_2018_idioms)] //! This crate provides facilities for parsing, printing and //! manipulating S-expression data. S-expressions are the format used //! to represent code and data in the Lisp language family. //! //! ```scheme //! ((name . "John Doe") //! (age . 43) //! (address //! (street "10 Downing Street") //! (city "London")) //! (phones "+44 1234567" "+44 2345678")) //! ``` //! //! `lexpr` also supports more complex types; including keywords and //! configurable tokens for `true`, `false` and `nil`, by default //! using Scheme syntax: //! //! ```scheme //! (define-class rectangle () //! (width //! #:init-value #nil ;; Nil value //! #:settable #t ;; true //! #:guard (> width 10) //! ) //! (height //! #:init-value 10 //! #:writable #f ;; false //! )) //! ``` //! //! Note that keywords, and the corresponding `#:` notation, is not //! part of standard Scheme, but is supported by `lexpr`'s default //! parser settings. //! //! There are three common ways that you might find yourself needing //! to work with S-expression data in Rust: //! //! - **As text data**. An unprocessed string of S-expression data //! that you receive from a Lisp program, read from a file, or //! prepare to send to a Lisp program. //! //! - **As an dynamically typed representation**. Maybe you want to check that //! some S-expression data is valid before passing it on, but without knowing //! the structure of what it contains. Or you want to handle arbirarily //! structured data, like Lisp code. //! //! - **As a statically typed Rust data structure**. When you expect all //! or most of your data to conform to a particular structure and //! want to get real work done without the dynamically typed nature //! of S-expressions tripping you up. //! //! Only the first two items of this list are handled by `lexpr`; for conversion //! from and to statically typed Rust data structures see the [`serde-lexpr`] //! crate. //! //! # Operating on dynamically typed S-expression data //! //! Any valid S-expression can be manipulated using the [`Value`] data //! structure. //! //! ## Constructing S-expression values //! //! ``` //! use lexpr::{Value, parse::Error}; //! //! # fn main() -> Result<(), Error> { //! // Some s-expressions a &str. //! let data = r#"((name . "John Doe") //! (age . 43) //! (phones "+44 1234567" "+44 2345678"))"#; //! //! // Parse the string of data into lexpr::Value. //! let v = lexpr::from_str(data)?; //! //! // Access parts of the data by indexing with square brackets. //! println!("Please call {} at the number {}", v["name"], v["phones"][1]); //! //! Ok(()) //! # } //! ``` //! //! # What are S-expressions? //! //! S-expressions, as mentioned above, are the notation used by various dialects //! of Lisp to represent data (and code). As a data format, it is roughly //! comparable to JSON (JavaScript Object Notation), but syntactically more //! lightweight. Also, JSON is designed for consumption and generation by //! machines, which is reflected by the fact that it does not specify a syntax //! for comments. S-expressions on the other hand, are intended to be written //! and read by humans as well as machines. In this respect, they are more like //! YAML, but have a simpler and less syntactically rigid structure. For //! example, indentation does not convey any information to the parser, but is //! used only to allow for easier digestion by humans. //! //! Different Lisp dialects have notational differences for some data types, and //! some may lack specific data types completely. This section tries to give an //! overview over the different types of values representable by the [`Value`] //! data type and how it relates to different Lisp dialects. All examples are //! given in the syntax used in [Guile](https://www.gnu.org/software/guile/) //! Scheme implementation. //! //! The parser and serializer implementation in `lexpr` can be //! tailored to parse and generate S-expression data in various //! "dialects" in use by different Lisp variants; the aim is to cover //! large parts of R6RS and R7RS Scheme with some Guile and Racket //! extensions, as well as Emacs Lisp. //! //! In the following, the S-expression values that are modeled by //! `lexpr` are introduced, In general, S-expression values can be //! split into the two categories primitive types and compound types. //! //! ## Primitive types //! //! Primitive, or non-compound types are those that can not //! recursively contain arbitrary other values. Numbers, //! strings and booleans fall into this category. //! //! ### Symbols and keywords //! //! Lisp has a data type not commonly found in other languages, namely //! "symbols". A symbol is conceptually similar to identifiers in other //! languages, but allow for a much richer set of characters than typically //! allowed for identifiers in other languages. Also, identifiers in other //! languages can usually not be used in data; Lisps expose them as a //! primitive data type, a result of the //! [homoiconicity](https://en.wikipedia.org/wiki/Homoiconicity) of the Lisp //! language family. //! //! //! ```scheme //! this-is-a-symbol ; A single symbol, dashes are allowed //! another.symbol ; Periods are allowed as well //! foo$bar!<_>? ; As are quite a few other characters //! ``` //! //! Another data type, present in some Lisp dialects, such as Emacs //! Lisp, Common Lisp, and several Scheme implementations, are //! keywords. These are also supported by `lexpr`. Keywords are very //! similiar to symbols, but are typically prefixed by `:` or `#:` and //! are used for different purposes in the language. //! //! ```lisp //! #:foo ; A keyword named "foo", written in Guile/Racket notation //! :bar ; A keyword named "bar", written in Emacs Lisp or Common Lisp notation //! ``` //! //! ### Booleans //! //! While Scheme has a primitive boolean data type, more traditional Lisps such //! as Emacs Lisp and Common Lisp do not; they instead use the symbols `t` and //! `nil` to represent boolean values. Using parser options, `lexpr` allows to //! parse these symbols as booleans, which may be desirable in some //! circumstances, as booleans are simpler to handle than symbols. //! //! ```scheme //! #t ; The literal representing true //! #f ; The literal representing false //! ``` //! //! ### The empty list and "nil" //! //! In traditional Lisps, the end of list is represented as by a //! special atom written as `nil`. In Scheme, the empty list is an //! atom written as `()`, and there `nil` is just a regular //! symbol. Both `nil` and the empty list are present and //! distinguishable in `lexpr`. //! //! ### Numbers //! //! Numbers are represented by the [`Number`] abstract data type. It can handle //! signed and unsigned integers, each up to 64 bit size, as well as floating //! point numbers. The Scheme syntax for hexadecimal, octal, and binary literals //! is supported. //! //! ```scheme //! 1 -4 3.14 ; A postive, negative, and a floating point number //! #xDEADBEEF ; An integer written using decimal notation //! #o0677 ; Octal //! #b10110 ; Binary //! ``` //! //! Scheme has an elaborate numerical type hierarchy (called "numeric tower"), //! which supports fractionals, numbers of arbitrary size, and complex //! numbers. These more advanced number types are not yet supported by `lexpr`. //! //! //! ### Characters //! //! Characters are unicode codepoints, represented by Rust's `char` data type //! embedded in the [`Value::Char`] variant. //! //! ### Strings //! //! ```scheme //! "Hello World!" //! ``` //! //! ## Lists //! //! Lists are a sequence of values, of either atoms or lists. In fact, //! Lisp does not have a "real" list data type, but instead lists are //! represented by chains of so-called "cons cells", which are used to //! form a singly-linked list, terminated by the empty list (or `nil` //! in tradional Lisps). It is also possible for the terminator to not //! be the empty list, but instead be af an arbitrary other data type. //! In this case, the list is refered to as an "improper" or "dotted" //! list. Here are some examples: //! //! ```scheme //! ("Hello" "World") ; A regular list //! ;; A list having with another, single-element, list as //! ;; its second item //! ("Hello" ("World")) //! (1 . 2) ; A cons cell, represented as an improper list by `lexpr` //! (1 2 . 3) ; A dotted (improper) list //! ``` //! //! Lists are not only used to represent sequences of values, but also //! associative arrays, also known as maps. A map is represented as a list //! containing cons cells, where the first field of each cons cell, called //! `car`, for obscure historical reasons, is the key, and the second field //! (`cdr`) of the cons cell is the associated value. //! //! ```scheme //! ;; An association list with the symbols `a` and `b` as keys //! ((a . 42) (b . 43)) //! ``` //! //! ## Vectors //! //! In contrast to lists, which are represented as singly-linked chains of "cons //! cells", vectors allow O(1) indexing, and thus are quite similar to Rusts //! `Vec` datatype. //! //! ```scheme //! #(1 2 "three") ; A vector in Scheme notation //! ``` //! //! ## Byte vectors //! //! Byte vectors are similar to regular vectors, but are uniform: each element //! only holds a single byte, i.e. an exact integer in the range of 0 to 255, //! inclusive. //! //! ```scheme //! #u8(41 42 43) ; A byte vector //! ``` //! //! [Serde]: https://crates.io/crates/serde //! [`serde-lexpr`]: https://docs.rs/serde-lexpr use proc_macro_hack::proc_macro_hack; /// Construct a [`Value`] using syntax similar to regular S-expressions. /// /// The macro is intended to have a feeling similiar to an implicitly /// quasiquoted Scheme expression. /// /// # Booleans /// /// ``` /// # use lexpr::sexp; /// /// let t = sexp!(#f); /// let f = sexp!(#t); /// ``` /// /// # Symbols and keywords /// /// Due to syntactic restrictions of Rust's macro system, to use /// kebab-case, you need to use the `#"..."` syntax. /// /// ``` /// # use lexpr::sexp; /// /// let sym = sexp!(symbol); /// let kw = sexp!(#:keyword); /// assert!(sym.is_symbol()); /// assert!(kw.is_keyword()); /// /// let kebab_sym = sexp!(#"kebab-symbol"); /// let kebab_kw = sexp!(#:"kebab-keyword"); /// assert!(kebab_sym.is_symbol()); /// assert!(kebab_kw.is_keyword()); /// ``` /// /// # Characters /// /// Characters can be written using Rust's character syntax: /// /// ``` /// # use lexpr::sexp; /// /// let ch = sexp!('λ'); /// assert!(ch.is_char()); /// assert_eq!(ch.as_char(), Some('λ')); /// ``` /// /// # Lists /// /// Lists can be formed by using the same syntax as in Lisp, including dot /// notation. /// /// ``` /// # use lexpr::sexp; /// /// let l1 = sexp!((1 2 3)); /// let l2 = sexp!((1 . (2 . (3 . ())))); /// let l3 = sexp!((1 2 . (3 . ()))); /// assert_eq!(l1, l2); /// assert_eq!(l2, l3); /// ``` /// /// Improper (aka dotted) lists are supported as well: /// /// ``` /// # use lexpr::sexp; /// let dotted = sexp!((1 2 . three)); /// assert!(dotted.is_dotted_list()); /// let tail = dotted.as_cons().unwrap().cdr(); /// assert!(tail.is_cons()); /// assert_eq!(tail, &sexp!((2 . three))); /// ``` /// /// # Vectors /// /// Vectors can be written using Scheme notation, e.g.: /// /// ``` /// # use lexpr::sexp; /// let v = sexp!(#(1 2 "three")); /// assert!(v.is_vector()); /// assert_eq!(v[2], sexp!("three")); /// ``` /// /// [`Value`]: enum.Value.html #[proc_macro_hack] pub use lexpr_macros::sexp; mod syntax; pub mod cons; pub mod datum; pub mod number; pub mod parse; pub mod print; pub mod value; #[doc(inline)] pub use self::parse::{ from_reader, from_reader_custom, from_slice, from_slice_custom, from_str, from_str_custom, Parser, }; #[doc(inline)] pub use self::print::{ to_string, to_string_custom, to_vec, to_vec_custom, to_writer, to_writer_custom, Printer, }; #[doc(inline)] pub use value::Value; #[doc(inline)] pub use datum::Datum; #[doc(inline)] pub use cons::Cons; #[doc(inline)] pub use value::Index; #[doc(inline)] pub use number::Number; #[cfg(test)] mod tests;