#+title: LangEvolve-rs
#+author: Lucien Cartier-Tilet

* Introduction
  LangEvolve-rs is a Rust rewrite of  the original [[https://github.com/ceronyon/LangEvolve/][LangEvolve project]] written by
  [[https://github.com/ceronyon/LangEvolve/][Ceronyon]]. This tool is  a conlanging tool used to apply  sound change rules on
  words or text.

* Differences with the original project
  The main  difference with  the main  project resides  in its  settings format:
  while  the  original project  only  supports  the  JSON format,  this  project
  supports both the JSON and the Yaml formats. The settings are also represented
  differently in  JSON between the  original project  and this one.  Lastly, the
  regex crate used  in this project does not allow  certain expressions, such as
  look-ahead and look-behind searches, and  backreferences. To get a better idea
  of what  I am talking about,  here is the  example json given by  the original
  project for Latin to Portugese:
  #+BEGIN_SRC json
    {
      "version" : "1",
      "categories" : {
        "V" : "aeiou",
        "L" : "āēīōū",
        "C" : "ptcqbdgmnlrhs",
        "F" : "ie",
        "B" : "ou",
        "S" : "ptc",
        "Z" : "bdg"
      },
      "rules" : [
        { "[sm]$" : "" },
        { "i(%V)" : "j\\1" },
        { "%L" : "%V" },
        { "(%Vr)e$" : "\\1" },
        { "(%V)v(%V)" : "\\1\\2" },
        { "u$" : "o" },
        { "gn" : "nh" },
        { "(%V)p(?=%V)" : "\\1b" },
        { "(%V)t(?=%V)" : "\\1d" },
        { "(%V)c(?=%V)" : "\\1g" },
        { "(%F)ct" : "\\1it" },
        { "(%B)ct" : "\\1ut" },
        { "(%V)pt" : "\\1t" },
        { "ii" : "i" },
        { "(%C)er(%V)" : "\\1r\\2" },
        { "lj" : "lh" }
      ]
    }
  #+END_SRC

  As you  can see, backreferences have  their syntax modified from  ~\1~ to ~$1~
  (or ~${1}~ if it is followed by  other stuff) for instance, and look-ahead and
  look-behind expressions must be incorporated into the expression.

  And here is the JSON generated by this project (beautified, the original is on
  one line only without unnecessary whitespace):
  #+BEGIN_SRC json
    {
        "version": "1",
        "categories": {
            "S": "ptc",
            "L": "āēīōū",
            "V": "aeiou",
            "Z": "bgd",
            "F": "ie",
            "C": "ptcqbdgmnlrhs",
            "B": "ou"
        },
        "rules": [
            ["[sm]$", ""],
            ["i(%V)", "j$1"],
            ["%L", "%V"],
            ["(%Vr)e$", "$1"],
            ["(%V)v(%V)", "${1}$2"],
            ["u$", "o"],
            ["gn", "nh"],
            ["(%V)p(%V)", "${1}b$2"],
            ["(%V)t(%V)", "${1}d$2"],
            ["(%V)c(%V)", "${1}g$2"],
            ["(%F)ct", "${1}it"],
            ["(%B)ct", "${1}ut"],
            ["(%V)pt", "${1}t"],
            ["ii", "i"],
            ["(%C)er(%V)", "${1}r$2"],
            ["lj", "lh"]
        ]
    }
  #+END_SRC

  By the way, here is the Yaml equivalent generated by this project:
  #+BEGIN_SRC yaml
    ---
    version: "1"
    categories:
      B: ou
      S: ptc
      L: āēīōū
      Z: bgd
      C: ptcqbdgmnlrhs
      F: ie
      V: aeiou
    rules:
      - - "[sm]$"
        - ""
      - - i(%V)
        - j$1
      - - "%L"
        - "%V"
      - - (%Vr)e$
        - $1
      - - (%V)v(%V)
        - "${1}$2"
      - - u$
        - o
      - - gn
        - nh
      - - (%V)p(%V)
        - "${1}b$2"
      - - (%V)t(%V)
        - "${1}d$2"
      - - (%V)c(%V)
        - "${1}g$2"
      - - (%F)ct
        - "${1}it"
      - - (%B)ct
        - "${1}ut"
      - - (%V)pt
        - "${1}t"
      - - ii
        - i
      - - (%C)er(%V)
        - "${1}r$2"
      - - lj
        - lh
  #+END_SRC

  Although most of the rules are not  between double quotes, it is preferable to
  write them as follows in order to avoid any issues with LangEvolveRs:
  #+BEGIN_SRC yaml
    ---
    version: "1"
    categories:
      B: ou
      S: ptc
      L: āēīōū
      Z: bgd
      C: ptcqbdgmnlrhs
      F: ie
      V: aeiou
    rules:
      - - "[sm]$"
        - ""
      - - "i(%V)"
        - "j$1"
      - - "%L"
        - "%V"
      - - "(%Vr)e$"
        - "$1"
      - - "(%V)v(%V)"
        - "${1}$2"
      - - "u$"
        - "o"
      - - "gn"
        - "nh"
      - - "(%V)p(%V)"
        - "${1}b$2"
      - - "(%V)t(%V)"
        - "${1}d$2"
      - - "(%V)c(%V)"
        - "${1}g$2"
      - - "(%F)ct"
        - "${1}it"
      - - "(%B)ct"
        - "${1}ut"
      - - "(%V)pt"
        - "${1}t"
      - - "ii"
        - "i"
      - - "(%C)er(%V)"
        - "${1}r$2"
      - - "lj"
        - "lh"
  #+END_SRC

  You can  find more  information on  how to use  regular expressions  with this
  project in the documentation of the regex crate [[https://docs.rs/regex/1.3.6/regex/][here]].

  The settings schema is set to  be fully backward-compatible. This means if the
  version number goes  up in the settings file, older  settings file will remain
  compatible with newer versions of the software. However, forward compatibility
  cannot be  ensured unless  someone invents time  travel, hence  settings files
  with  a higher  version  than  the running  software’s  will be  automatically
  rejected.

* License
  LangEvolveRs is  licensed under the  AGPLv3 license.  The full license  can be
  found [[file:agpl-3.0.txt][here]].