Hyperpolyglot Lisp: Common Lisp, Racket, Clojure, Emacs Lisp

grammar and execution | variables and expressions | arithmetic and logic | strings | regular expressions | dates and time | lists | fixed-length arrays | dictionaries | user-defined types | functions | execution control | exceptions | streams | emacs buffers | files | directories | processes and environment | libraries and namespaces | objects | lisp macros | reflection | java interop Versions used to verify examples in the reference sheet. Compiling a.ss creates the byte-code compiled file a_ss.zo, which will be used by mzscheme in preference to the source code if it encounters In order for code to be compiled as a standalone executable, it must be packaged as a module. This can be accomplished by putting the #lang scheme shorthand the top of the file. All functions that are defined in the module will be executed in order. Here is a simple example: #lang scheme (define hello (printf "Hello world!~n")) emacs How to have a script run by the interpreter automatically. Replace the given path with the path to the interpreter on your system. To run some lisp code from within emacs, use M-x load or M-x load-file. The first command will use the list of strings in load-path to search for the file. It is not necessary to specify the .el or .elc suffix if the file has one. The following snippet is an emacs lisp shebang script implementation of cat: #!/usr/bin/env emacs --script (condition-case nil (let (line) (while (setq line (read-from-minibuffer "")) (princ line) (princ "\n"))) (error nil)) An implementation of echo: #!/usr/bin/env emacs --script (condition-case nil (progn (dotimes (i (length argv) nil) (princ (nth i argv)) (princ " ")) (princ "\n")) (error nil)) How to invoke the repl from the command line. Racket also provides a GUI repl environment called DrRacket. The clojure repl saves the result of each evaluation in the variables *1, *2, … and the last exception in *e. How to pass in a program to be executed on the command line. What is used to separate the operator and data of a S-expression. In lisps other than clojure, any character can be used in a symbol. Some characters are special to the reader and must be escaped to include them in a symbol. The reader will interpret a sequence of characters starting with a digit as a number instead of a symbol, so escaping must be used to create such a symbol. Common Lisp is case insensitive, and the reader converts all letters to upper case. A symbol consisting of just periods "." must be escaped. Symbols that start and end with an asterisk "*" may conflict with system defined special variables. # is only disallowed by the reader at the beginning of symbols. A symbol consisting of a single period must be escaped. #| |# delimited comments in Common Lisp and Scheme can span multiple lines, and thus can be used to comment out code. Code with balanced parens can be commented out in the following manner: Are identifiers case sensitive; which characters can be used in identifers. In Lisp, identifiers are called symbols. How to quote or escape characters in identifiers which are otherwise prohibited. nil and the empty list '() are identical. null and the empty list '() are identical. nil and the empty list '() are distinct. nil and the empty list '() are identical. In Lisp, identifiers are first class values and can be stored in variables. When used as an argument, the Lisp interpreter will treat an identifier as the value of the variable associated with the identifier unless special syntax is used. How to test whether a value is an identifier. A non-referential identifier is an identifier whose value is itself. Non-referential identifiers are called keywords in Lisp. They also appear in Prolog, where they are called atoms, and Ruby, where they are called symbols. A non-referential identifier can be convenient to use as a key in a dictionary, since it doesn't have to single quote escaped. Strings are an alternative to non-referential identifiers; some languages have string interning which makes the use of strings just as efficient as non-referential identifiers. In Common Lisp, there is a dictionary of attributes associated with each identifier called a property list. Clojure metadata is stored with a value which is an instance of clojure.lang.IObj. Many types are subclasses of clojure.lang.IObj, but integers, floats, and strings are not. Clojure metadata is immutable: all keys must be set at once and there is no way to remove keys. The different cell types. A lisp-1 only stores a single entity under a symbol in a given environment. A lisp-2 stores multiple entities, and which entity a symbol will resolve to depends on how the symbol is used. In particular, a value and a function can be stored under the same symbol without collision. (eq nil ()) is true in common lisp and emacs lisp. Keywords are pre-defined symbols that evaluate to their printed representation. The reader recognizes them by the initial colon, or in the case of Scheme

Hyperpolyglot Lisp: Common Lisp, Racket, Clojure, Emacs Lisp

Key takeaways

More in computer-science