#+title: Half-Broken Car in Heavy Traffic
#&summary
An esoteric programming language with compiler/interpreter
#&
#+license: bysa, text
#+license: agpl 3+, program
#&toc

* Half-Broken Car in Heavy Traffic

Half-Broken Car in Heavy Traffic is a difficult programming language with only
5 combined operators and direction "signs" for 2D grids.

hbcht is a Python 3.1+ combined compiler/interpreter for the language.

** Example program

#+BEGIN_SRC
; Increment the first memory cell once without changing the other cells.

     >   ^ <
       >   v   <
         #
         ^< >
            ^
     ^      ^<>
              ^
           >  ^<
           ^  
   > v < o v
           v
           v
           < > v
     v   v
     v   v
     v   v
     v   v
         >  ^ <
#+END_SRC

When compiled, this can be called as
: ./test 51
which will return
: 0: 52
because 51 + 1 = 52.

** Language documentation

This is the official documentation of HBCHT.

HBCHT is a 2D grid-based programming language. You are a car fighting to get to
the exit of a very chaotic highway. You have to follow the signs, but whenever
you do that, you also change your memory. The value of your current memory cell
can be incremented or decremented and your memory cell index can change. You
can also find signs that tell you to turn either right or not turn at all,
depending on your memory.

The car can drive in four directions: up, right, down, and left. Because of the
chaos, you never know which direction the car is headed when the program
starts. This makes it easy to randomize the output.

To make things worse (actually, it's to make programming in HBCHT possible),
you cannot turn left because your car is half-broken. You can drive straight
ahead, you can turn right, and you can reverse.

*** Markers

: o car
: # exit, return/print

*** Operations

: > go right, next memory cell
: < go left, previous memory cell
: ^ go up, increment
: v go down, decrement
: / go right if the current memory cell has the same value as the previous
:   memory cell, else continue (if the previous memory cell does not exist,
:   its value is zero)

*** Rules

+ There can be only one car and only one exit
+ The car cannot turn left; any relative left turns will be ignored along with
  their memory effects
+ The program always starts at memory cell #0
+ All memory cells have the value 0 by default
+ Input values cannot be negative, but values returned by a program can
+ The car cannot go out of bound; if it exits to the right, it reenters to the
  left, etc.
+ Values cannot be input to memory cells below memory cell #0, but the program
  can set values in these
+ Values can be arbitrarily large. An interpreter or compiler without this
  feature is valid, but not perfect (note that hbcht's C translator uses
  32-bit ints and is thereby not perfect).

A semicolon denotes a comment. Anything from the semicolon to the end of the
line is ignored.

If a program file contains a line that starts with =@intext=, it will see
input as text and convert the text to ordinals before running the core
function.

If a program file contains a line that starts with =@outtext=, it will show
output as a text string instead of a list of numbers.


** Download

hbcht is released under the AGPLv3+.

[[hbcht-0.1.0.tar.gz][Download]].

hbcht can also be found in the [[http://pypi.python.org/pypi/hbcht][Python Package Index]]. hbcht has its code at
Gitorious; see [[http://gitorious.org/hbcht]].

