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Insert units and constants into source code, with GNU Emacs
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cdominik/constants-for-Emacs
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Commentary: When I write small programs to calculate something, I often need the values of some physical constants and units. I could of course always link a big module with all those definitions. But often I want the program to run stand-alone, so I prefer to define variables for these constants directly. This package provides the command `constants-insert'. It prompts for one or more variable names and inserts definition statements for numerical constants into source code. It does this in the appropriate syntax for many different programming languages. There are also the commands `constants-get' and `constants-replace' which just display the value of a constant in the echo area, or replace the name of a constant in a buffer with its value. The package knows many constants and units, both in the SI and in the cgs unit system. It also understands the usual unit prefixes (like "M" for Mega=10^6 or "m" for milli=10^-3). So the built-in constant "pc" (parsec, an astronomical distance), can also be used in kpc (1000 pc), Mpc (10^6 pc) etc. For a full list of all available constants, units, and prefixes, use `M-x constants-help', or press "?" while the command is prompting for names. The unit system (SI or cgs) can be selected using the option `constants-unit-system'. Additional constants or units can be defined by customizing `constants-user-defined'. You can tell the package to use different names for some of the constants (option `constants-rename'), and you may also specify a different variable name on the fly (see "Mlunar" in the example below). The code inserted into the buffer is mode dependent. Constants.el has defaults for some programming languages: FORTRAN, C, IDL, MATLAB, OCTAVE, PERL, EMACS-LISP, GP. You can change these defaults and add definitions for other languages with the variable `constants-languages'. INSTALLATION ------------ Put this file on your load path, byte compile it, and copy the following code into your .emacs file. Change the key definitions, variable name aliasing and the unit system to your liking. (autoload 'constants-insert "constants" "Insert constants into source." t) (autoload 'constants-get "constants" "Get the value of a constant." t) (autoload 'constants-replace "constants" "Replace name of a constant." t) (define-key global-map "\C-cci" 'constants-insert) (define-key global-map "\C-ccg" 'constants-get) (define-key global-map "\C-ccr" 'constants-replace) (setq constants-unit-system 'SI) ; this is the default ;; Use "cc" as the standard variable name for speed of light, ;; "bk" for Boltzmann's constant, and "hp" for Planck's constant (setq constants-rename '(("cc" . "c") ("bk" . "k") ("hp" . "h"))) ;; A default list of constants to insert when none are specified (setq constants-default-list "cc,bk,hp") USAGE ----- In a programming mode, call the function and at the prompt enter for example Name[, Name2...}: cc,k,Mlunar=Mmoon,Mpc In a FORTRAN buffer, this would insert doubleprecision cc=2.99792458d8 ! Speed of light [SI] doubleprecision k=1.3806503d-23 ! Boltzmann's constant [SI] doubleprecision Mlunar=7.35d22 ! Moon mass [SI] doubleprecision Mpc=3.085677582d+22 ! Mega-Parsec [SI] while in a C buffer you would get double cc=2.99792458e8; /* Speed of light [SI] */ double k=1.3806503e-23; /* Boltzmann's constant [SI] */ double Mlunar=7.35e22; /* Moon mass [SI] */ double Mpc=3.085677582e+22; /* Mega-Parsec [SI] */ When entering the names, you can optionally precede a name with "varname=", in order to change the variable name that will be used for the definition. While entering the name of a constant, you can use completion. Press `?' during completion to display a detailed list of all available constants. You can scroll the Help window with S-TAB while entering text in the minibuffer. If you add "si" or "cgs" to the comma-separated list of constant/unit names, this will switch the unit system for the burrent buffer and editing session. CUSTOMIZATION ------------- The following customization variables are available: constants-unit-system The unit system to be used for the constants (`cgs' or `SI'). constants-rename Alist with additional names for some existing constants. constants-user-defined User defined constants. constants-default-list Default constants to insert if none are specified. constants-languages Format descriptions for different major programming modes. constants-indent-code Non-nil means, indent the newly inserted code according to mode. constants-allow-prefixes Non-nil means, interpret prefixes like M (mega) etc. constants-prefixes Allowed prefixes for constants and units. CONTEXT SENSITIVITY ------------------- For some languages, it might be usefull to adapt the inserted code to context. For example, in Emacs Lisp mode, the default settings insert "(VARIABLE VALUE)" with surrounding parenthesis for a `let' form. However, if you'd like to use this in a `setq' form, the parenthesis are incorrect. To customize for such a case, set the variable `constants-language-function' to a function which returns, after checking the context, the correct language entry of the form (MAJOR-MODE FORMAT EXP-STRING PREFIX-EXPRESSION). For the above example, you could do this: (defun my-constants-elisp-function () "Check context for constants insertion." (save-excursion (condition-case nil (progn (up-list -1) (if (looking-at "(setq\\>") '(emacs-lisp-mode "%n %v%t; %d %u" "e" "(* %p %v)") '(emacs-lisp-mode "(%n %v)%t; %d %u" "e" "(* %p %v)"))) (error nil)))) ; return value nil means use default ;; The variable is buffer-local and must be set in the mode hook. (add-hook 'emacs-lisp-mode-hook (lambda () (setq constants-language-function 'my-constants-elisp-function))) BUGS ---- - Completion does not consider prefixes. For example, you cannot complete "MGa" to "MGauss" (meaning "Mega-Gauss"). This was not implemented because it would cause too many matches during completion. But you can still use completion for this by separating the prefix from the unit with a star: After typing "M*Ga", completion will work and result in "M*Gauss". Both "MGauss" and "M*Gauss" will result in a variable "MGauss" being defined. - When using cgs units, be very careful with the electric constants and units. This library uses E.S.U., not E.M.U. Note that the *equations* involving charges, currents and magnetism are all different for SI, CGS/ESU and CGS/EMU. So when switching to a different system, you must make sure to use the right equations. - I have tried to implement the cgs units correctly, but I have some doubt about the electrical and radiation units. Double-check before blindly using these. AUTHOR ------ Carsten Dominik <carsten.dominik@gmail.com> Let me know if you are missing a constant in the default setup, if you notice that a value of a constant is not correct, or if you would like to see support for another language mode. ACKNOWLEDGEMENTS ---------------- Thanks to Kees Dullemond. Watching him writing programs has inspired this package. Thanks to the following people for reporting bugs and/or suggesting features/constants/languages: Bruce Ignalis, Dave Pearson, Jacques L'helgoualc'h, Federico Beffa CHANGES ------- Version 2.10 - Ready for becoming an ELPA package Version 2.8 - Allow the interactive prompt to change the unit system. That change will be stored locally for the current buffer and editing session. Version 2.7 - Add support for Python Version 2.5 - Better Lisp indentation (patch by Federico Beffa <beffa@ieee.org>) Version 2.3 - Add a few more constants Version 2.0 - New commands `constants-get' and `constants-replace'. Version 1.8 - Completion now preserves up/downcase as typed. - Completion with prefixes can be done, by adding a star as in "M*Gauss". - A different variable name may be specified directly at the prompt with the syntax "varname=const". - Support for shell-like modes like idlwave-shell-mode. - XEmacs support (fixed a small bug) TO DO ----- - Support more programming languages. - Add expression values tcl and others. - Add calc mode? - add these units? - g[u]age, - (circular) mill - ampere-turn - add a command to get info about a certain variable. Only useful if the variable name really is the constant name. Not sure if this will be used at all, so until someones asks for it, this will not be done. ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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