_,            
                    | |            
   __ _,  ___ ,_ __ | | __ _,  _,     /\___     
  / _` | / _ \| '__)| |/ /| | | |    (    @\___ 
 ( (_) |(  __/| |   |   ( | |_| |   /          )
  \_,  | \___)|_|   |_|\_\ \__,_|  /    (_____/ 
  __/  |                          (_____/    U  
 (____/ 

An interepreter for Concatenative Combinators as described in:

"The Theory of Concatenative Combinators by Brent Kerby" (link)

gerku started as sidekick project of mlatu to check if using stack based semantics would be equivalent to using rewriting rules. Given the type of rewriting rules mlatu is aiming to handle, the answer is NO!

mlatu is a project by Caden Haustein (carmysilna) (link)

gerku is now only aimed to be a tool for those wanting to explore the concatenative Combinatory Logic described in the Kerby's article.

Visit this channel on Discord to discuss and provide feedback.

Clone (or fork) the repository on Github.

In the src directory just type make (tested on linux and on Windos MSYS2)

   prj/gerku/src> make
   prj/gerku/src> ./gerku

All dependencies are in the src/libs directory, all libraries used are by me except linenoise, a small, fast, self-contained, MIT-licensed, replacement of readline.

If the terminal you're using has issues with linenoise, you can change the settings in the makefile comment the line:

LINENOISE=-DUSE_LINENOISE

and recompile. You will lose history and line editing features.

gerku has few options that can be specified on the command line:

prj/gerku/src> ./gerku -h
GERKU 0.0.6-beta (C) 2021 https://github.com/rdentato/gerku
Usage: gerku [OPTIONS] ...
   -d file      Load definitions from the specified file
   -r           Run mode (no REPL)
   -v           Version

All arguments after the options are considered to be source files to be loaded and executed before entering the REPL. The directory grk has some example.

The list of REPL commands is accessible within the REPL iteself:

prj/gerku/src> ./gerku
GERKU 0.0.6-beta (C) 2021 https://github.com/rdentato/gerku
Type ! for available commands.
|-> 
gerku> !
Available commands:
  !help              this help
  !list              list of defined words
  !load file         load definitions from file
  !save file         save definitions to file
  !print             print current stack
  !trace             toggle reduction tracing
  !quit              exit the repl
  !def ...           define a new word
  !del word | !all   delete a word [all words!]
  !wipe [auto]       wipe the stack [and toggles autowipe]
|-> 

A new combinator is defined through the "!def" command:

prj/gerku/src> ./gerku -h
./gerku -d
GERKU 0.0.6-beta (C) 2021 https://github.com/rdentato/gerku
Type ! for available commands.
|-> 
gerku> !def (@) (@) COMB = ((@1) @2)
|-> 
gerku> !list
        (@) (@) COMB = ((@1) @2)
|-> 
gerku> (x) (y) COMB
|-> ((x) y) 

By default gerku loads the definitions stored in grk/default.grk.

You can load a different definition file using the -d flag.

For example if you only want to load the primitive Kerby's combinators.

  prj/gerku/src> ./gerku -d grk/kerby.grk