As no one has stepped up with a solution that would allow the module to keep using let or lexical let without breaking them for the rest of emacs, i am accepting stefans answer, which states that the above macro is the way to do it. Newest lexicalscoping questions emacs stack exchange. I asked rms when he was implementing emacs lisp why it was dynamically scoped and his exact reply was that lexical scope was too inefficient. Returning a deferred object in the deferred tasks, the returned task is executed before the next deferred one that is statically connected on the source code. Forcing lexical scope in the middle of dynamic scope today i ran head first into lexical vs dynamic scope in emacs lisp. Before emacs 24 introduced closures, i found lexical let useful for making closures when necessary i. Feb 28, 2016 this is because every iteration itself is a new block scope. It enables the compilation of existing programs written in emacs lisp into more modern programming languages using lexical scoping. I suspect that in this case that there isnt much difference, but i dont.
This happens by default if a suitable support library is found at build time, like libacl on gnulinux. Lexical scope, closures, function scope and block scope. Dynamic scope means to use the environment where the function is called. Closure is the mechanism of a function remembering its lexical scope even when the functions is referenced elsewhere and even after the parent function has returned. After all, a picture is worth five hundred hello worlds. Dynamic scope analysis is a new variant of a class of known analysis techniques called constraintbased flow. In most of the modern programming languages only lexical scope is supported. This is the scope you will be using in clojure the vast majority of the time.
While this was never hugely popular among elisp programmers, it did work, creating real and efficient closures, as long as you remembered to wrap them in lexical let, as in this. Citeseerx document details isaac councill, lee giles, pradeep teregowda. Scope rules define the visibility rules for names in a programming language. Abstract dynamic scope analysis is a static analysis for emacs lisp programs. In addition to that, the answer improves on my code by using boundandtruep and adding an elegant declaration for edebug and lispindent. With lexical scope we can access variables defined in. To use it, set the bufferlocal variable lexicalbinding to a nonnil value. Manuals written in the gnu texinfo system can also be converted to info files suitable for reading online with emacs or stand. Consequently, a good idiomatic translation of emacs lisp into, say, scheme, should convert these binding constructs into the corresponding lexical binding constructs of the target substrate. Lexical binding is sometimes called static binding. Can anybody explain me how eval works with emacs24. If you write a code of deferred tasks without lexical scope macros, you should be careful with the scopes of each variables. Using lexical binding gnu emacs lisp reference manual.
Jan 17, 2015 well, if you just dig deeper into how a compiler works, you will see how js scope is defined, leading you to understand not just scope, but also hoisting and closures without the mystery or magic. As no one has stepped up with a solution that would allow the module to keep using let or lexicallet without breaking them for the rest of emacs, i am accepting stefans answer, which states that the above macro is the way to do it. For many lets and other binding constructs in real emacs lisp code, dynamic scope and lexical scope are identical. Im worried that if i started using emacs, id start hacking the elisp which id be terribly good at, and hate the lack of lexical scope, etc. For a discussion, see dynamicbindingvslexicalbinding emacs 24 has optional lexical binding, which can be enabled on a perbuffer basis. In languages with lexical scope also called static scope, name resolution depends on the location in the source code and the lexical context, which is defined by where the. It is possible to translate code written in emacs lisp or another lisp dialect which uses dynamic scoping to a more modern programming language with lexical scoping while largely preserving structure and readability of the code. Using dynamic vars also breaks referential transparency, which greatly reduces code readability and testability. I am also glad that emacs now supports lexical scoping and closures as an optin feature on filebyfile basis, although special variables. Before emacs 24, the easiest way to get closures was by using the lexical let form defined in clmacs, which emulated lexical scope with some clever macro trickery. Also note that in lisp, a symbols binding has lexical scope, not the mapping from an identifier to a symbol. However, special variables are still dynamically bound. Contribute to kiwanami emacs deferred development by creating an account on github.
A lexical binding has lexical scope, meaning that any reference to the variable must be located textually within the binding construct 1. Emacs stack exchange is a question and answer site for those using, extending or developing emacs. Today ill be looking at closures and lexical scoping. The word lexical means, in a broad sense relating to text, and clearly we have defined scope as being a relationship involving text, so is this kind of scoping also called lexical scoping. Forcing lexicalscope in the middle of dynamicscope today i ran head first into lexical vs dynamic scope in emacs lisp. Semantic is an infrastructure for parser based text analysis in emacs. Lexical vs dynamic scope in clojure the data point. Only when you exactly know how scoping works in yo. The important scope and extent rules in common lisp follow. A private variable is a variable declared in a manner compatible with this definition. Download relevant zip file and unzip in some nice dir. Variable bindings for which there is a dynamicextent declaration also have lexical scope and indefinite extent, but objects that are the values of such bindings may have dynamic extent. As one of the more overused jargon terms in programming languages, i get a lot of questions about it.1145 1098 491 1554 1144 50 460 815 1558 1271 200 593 1287 941 609 40 389 194 189 826 1511 1083 1387 783 920 1482 193 1072 623 621 1488 722 995 389 919 514 658 837 1421 1255 913 971