translate


* Introduction

  =TRANSLATE= is a thin abstraction layer over the ordinary strings
  which allows the creation of a seamless translation for your
  project. The code is written in a plain Common Lisp without any
  dependencies. A system definition is provided in =ASD= format,
  although =ASDF= isn't required to run this software.

  This library is licensed under =LLGPLv2=, which means that it may be
  used in any project for any purpose although any significant
  modifications to the library should be published. It doesn't impose
  it's license on software depending on it.

  To illustrate library usage some imaginary functions are used:
  =MAKE-BUTTON= and =MAKE-LABEL=. The following sample code convention
  is used:

  - lines preceded with ==> indicate *reader* input
  - all other lines represent *printer* output

* Description

** Basic usage

   The library pollutes =*READTABLE*= with dispatch macro character
   =#t=, where "t" is abbreviation of "translate". Instead of writing
   ordinary constant strings in his/her application, the user instead
   precedes them with =#t=:

   #+BEGIN_SRC lisp
     ==> #t"dum dum dum, piję rum"
     "la la la, I drink in the spa"
   #+END_SRC

   If =TRANSLATE:*LANGUAGE*= is bound to =NIL= and
   =TRANSLATE:*RESOLUTION-TIME*= to =:LOAD-TIME=, then =#t="hello"
   will resolve to the string "hello" and the translation will have no
   effect. It is convenient, because programmer can put =#t="strings"
   for the future translation with no functional consequences at
   run-time while keeping application innards visually separated from
   the messages meant to be presented to user.

   #+BEGIN_SRC lisp
     ==> (setf translate:*language* nil)
     NIL

     ==> (make-button :label #t"hello")
     #<button "hello">
   #+END_SRC

   Binding =TRANSLATE:*LANGUAGE*= to a non-NIL value enables string
   translation. If no translation exists it will be temporarily
   translated to the same value enclosed in a curly brackets:

   #+BEGIN_SRC lisp
     ==> (translate:define-language :pl)
     (#<hash-table 00000000054323c0> NIL #<compiled-function 0000000005fe08c0>)

     ==> (setf translate:*language* :pl)
     :PL

     ==> (make-label :text #t"Greetings, programs")
     ;;; Warning: phrase "Greetings, programs" isn't defined for language :PL.
     #<label "{Greetings, programs}">

     ==> (make-label :text #t"Leave the grid")
     ;;; Warning: phrase "Leave the grid" isn't defined for language :PL.
     #<label "{Leave the grid}">
   #+END_SRC

   Using a string that has not been translated will cause a warning at
   resolution time and string will be added to the special list of
   phrases not yet translated (which may be evaluated for future
   processing, like adding the missing translations). If a language
   put in the =TRANSLATE:*LANGUAGE*= isn't defined yet, =CERROR= will
   be signaled with a restart allowing language creation.

   To distinguish dictionaries, the predicate =EQL= is used and
   phrases are distinguished using the predicate =EQUAL=, so the most
   convenient is using symbols as the language designators. It also
   implies, that phrases meant for translation are case sensitive.

** Adding translation

   To add translations, two interfaces are provided. The
   =ADD-SINGLE-TRANSLATION= function takes three arguments, where the
   first is the language for which we provide translation, the second
   is a translated phrase and the third is an actual
   translation. Phrase type must be a string, but the translation
   might be any kind of object (although it is advised to use strings,
   the user is free to shoot himself in the foot by abusing the
   translation mechanism).

   #+BEGIN_SRC lisp
     ==> (translate:add-single-translation 'pl "hello" "Witaj!")
     ;;; Warning: Implicitly creating language PL.
     [PL] hello -> Witaj!
     "Witaj!"

     ==> (translate:add-single-translation 'en "hello" "Welcome!")
     ;;; Warning: Implicitly creating language EN.
     [EN] hello -> Welcome!
     "Welcome!"

     ==> (translate:add-single-translation
          'pl "bang"
          (let ((i 1))
            (lambda ()
              (format nil "bah ~A" (incf i)))))
     bang -> #<bytecompiled-closure #<bytecompiled-function 00000000067d9f50>> (PL)
     #<bytecompiled-closure #<bytecompiled-function 00000000067d9f50>>
   #+END_SRC

   =ADD-TRANSLATIONS= is a simple wrapper around
   =ADD-SINGLE-TRANSLATION= that allows the translation of multiple
   phrases in one form. The first argument is once again the
   translation language, while all further arguments are alternately
   phrases and translations.

   #+BEGIN_SRC lisp
     ==> (translate:add-translations 'pl
            "header-about"   "O firmie"
            "header-offer"   "Oferta"
            "header-blog"    "Blog"
            "header-pricing" "Cennik"
            "header-contact" "Kontakt")
     [PL] header-about -> O firmie
     [PL] header-offer -> Oferta
     [PL] header-blog -> Blog
     [PL] header-pricing -> Cennik
     [PL] header-contact -> Kontakt
     T

     ==> (translate:add-translations 'en
            "header-about"   "About"
            "header-offer"   "Offer"
            "header-blog"    "Blog"
            "header-pricing" "Prices"
            "header-contact" "Contact")
     [EN] header-about -> About
     [EN] header-offer -> Offer
     [EN] header-blog -> Blog
     [EN] header-pricing -> Prices
     [EN] header-contact -> Contact
     T
   #+END_SRC

   Generally it is advised to use symbolic and meaningful names for
   phrases to be translated, not the final phrases written in English.
   Providing "translation-tags" of concise form is easier to
   comprehend for people who will translate the application.

** Interactive fixing of the missing phrases

   Loading the code is enough to catch all not yet translated phrases
   for the active language (bound to =TRANSLATE:*LANGUAGE*=) if
   resolution is performed at load time. Otherwise, an untranslated
   phrase is saved after it's first evaluation. To list saved phrases
   without translations, the function =MISSING-TRANSLATIONS= is
   available. It returns a list of the form ={((LANG (PHRASES*))*)}=.

   #+BEGIN_SRC lisp
     ==> (translate:missing-translations)
     ((PL ("phrase-1" "phrase-2" "phrase-3"))
      (BG ("phrase-1" "phrase-3")))
   #+END_SRC

   Such output means, that language =PL= doesn't have translations for
   "phrase-1", "phrase-2" and "phrase-3", while =BG= doesn't have
   translations for "phrase-1" and "phrase-3". Languages which have
   all translations are filtered and they don't appear in the result.

** Different times of the resolution

   The library may work in two different modes which dictate the time
   when the actual translation is performed. Strings may be translated
   at load-time, or at run-time.

   The first approach is faster, because it doesn't require any
   processing at run-time, while the second is much more flexible
   allowing the change of dictionaries and translations when the
   program is running or depending on lexically scoped value of the
   parameter =TRANSLATE:*LANGUAGE*=.

   It is important to remember that, when translations are done at
   run-time, strings preceded by =#t= are transformed to the function
   calls and they may work not as expected in the context where
   enclosing macro prevents their evaluation.

   #+BEGIN_SRC lisp
     ==> (setf translate:*resolution-time* :run-time)
     :RUN-TIME

     ==> (setf translate:*language* :en)
     :EN

     ==> (translate:add-single-translation :en "hello" "Hello")
     [EN] hello -> Hello

     ==> (translate:add-single-translation :pl "hello" "Cześć")
     [PL] hello -> Cześć

     ==> (let ((translate:*language* :en))
           #t"hello")
     "Hello"

     ==> (let ((translate:*language* :pl))
           #t"hello")
     "Cześć"

     ==> (quote #t"hello")
     (TRANSLATE:TRANSLATE "hello")
   #+END_SRC

   When translation is performed at load-time, the translation has to
   be present before the actual phrase is used (e.g. in a lambda
   expression), because phrases are resolved to their translations
   immediately. That also means that changing =TRANSLATE:*LANGUAGE*=
   in the future won't affect translations resolved earlier.

   #+BEGIN_SRC lisp
     ==> (setf translate:*resolution-time* :load-time)
     :LOAD-TIME

     ==> (setf translate:*language* :en)
     :EN

     ==> (defparameter *my-function-1*
           (lambda () #t"hello"))
     ;;; Warning: phrase "hello" isn't defined for language EN.
     *MY-FUNCTION-1*

     ==> (translate:add-single-translation :en "hello" "Hello")
     hello -> Hello (EN)

     ==> (translate:add-single-translation :pl "hello" "Cześć")
     hello -> Cześć (PL)

     ==> (let ((translate:*language* :en))
           #t"hello")
     "Hello"

     ==> (let ((translate:*language* :pl))              ; lexical scope is ignored
           #t"hello")
     "Hello"

     ==> (defparameter *my-function-2*
           (lambda () #t"hello"))
     *MY-FUNCTION-2*

     ==> (funcall *my-function-1*) ; phrase wasn't translated when function was created
     "{hello}"

     ==> (funcall *my-function-2*)
     "Hello"

     ==> (quote #t"hello")
     "Hello"
   #+END_SRC

   Translation at run-time is better when the programmer wants to add
   translations ad-hoc or wants to switch languages when the
   application is running. Load-time translation is more suitable for
   static translations for deployed applications or where macros
   prevent necessary evaluation of the expressions. Also when the
   programmer wants to add translations in future (if language is
   bound to nil and resolution is performed at load-time the
   expression =#t="hello world" means the same as the "hello world").

* Reference
** Parameters
*** =*LANGUAGE*=
    #+BEGIN_SRC text
      This variable holds the current language designator (the predicate
      used for comparison is EQL). If bound to NIL, translation works the
      same way as the IDENTITY function.
    #+END_SRC

*** =*RESOLUTION-TIME*=
    #+BEGIN_SRC text
      Applicable values are :LOAD-TIME and :RUN-TIME (the latter is the
      default). The variable controls time of actual resolution.

      If it's the :LOAD-TIME, then resolution is performed when the reader
      encounters the #t dispatch macro character, while setting the variable
      to :RUN-TIME translates #t"string" to the form (TRANSLATE "string")
      and resolution takes place at the time of the form evaluation.
    #+END_SRC

** Functions
*** DEFINE-LANGUAGE
    #+BEGIN_SRC text
      DEFINE-LANGUAGE - external symbol in TRANSLATE package
      -----------------------------------------------------------------------------
      DEFINE-LANGUAGE (NAME &REST TRANSLATIONS)                          [Function]
      Define language NAME with provided TRANSLATIONS

      If LANGUAGE exists, a continuable error is signalled, which allows either
      dropping the operation or superseding the language which is already defined.
      TRANSLATIONS are alternating phrases and their corresponding objects.
      -----------------------------------------------------------------------------
    #+END_SRC

*** ADD-SINGLE-TRANSLATION
    #+BEGIN_SRC text
      ADD-SINGLE-TRANSLATION - external symbol in TRANSLATE package
      -----------------------------------------------------------------------------
      ADD-SINGLE-TRANSLATION (LANGUAGE PHRASE TRANSLATION)               [Function]
      Add TRANSLATION of PHRASE for given LANGUAGE

      If LANGUAGE doesn't exist, it is implicitly created and a warning is
      emmited.
      -----------------------------------------------------------------------------
    #+END_SRC

*** ADD-TRANSLATIONS
    #+BEGIN_SRC text
      ADD-TRANSLATIONS - external symbol in TRANSLATE package
      -----------------------------------------------------------------------------
      ADD-TRANSLATIONS (LANGUAGE &REST TRANSLATIONS)                     [Function]
      Add any number of TRANSLATIONS for the given LANGUAGE
      -----------------------------------------------------------------------------
    #+END_SRC

*** TRANSLATE
    #+BEGIN_SRC text
      TRANSLATE - external symbol in TRANSLATE package
      -----------------------------------------------------------------------------
      TRANSLATE (PHRASE &OPTIONAL (LANGUAGE *LANGUAGE*))                 [Function]
      Find the translation of PHRASE in the store associated with LANGUAGE

      If LANGUAGE is NIL, then this is the same as the IDENTITY function. If
      the provided LANGUAGE isn't defined, the store is explicitly
      created. If no PHRASE is defined for a given language, it is stored
      for later translation and replaced by PHRASE surrunded by curly
      brackets.
      -----------------------------------------------------------------------------
    #+END_SRC

*** MISSING-TRANSLATIONS
    #+BEGIN_SRC text
      MISSING-TRANSLATIONS - external symbol in TRANSLATE package
      -----------------------------------------------------------------------------
      MISSING-TRANSLATIONS                                               [Function]
      Creates a list of phrases which aren't translated for the defined
      languages. Returns a list of form: ({(LANG ({PHRASE}*))}*)
      -----------------------------------------------------------------------------
    #+END_SRC


translate

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translate

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