Scala external DSL for the esoteric programming languages brainfuck and whitespace

PL assignment 5

Siddharth Kumar Eugene Ng Quinten McNamara

BR__NF_CK: a crossover language between the brainfuck and whitespace programming languages

For every program there exist two memory representations.
There is a stack that the programmer can use whitespace language to operate on.
There is also an array of cells that the programmer can use brainfuck language to operate on.
These two features exist separately and independently.

These structures and the syntax for these languages are not modified.

Brainfuck: 10 commands: > < + - . ! , ` [ ]
Whitespace: 5 Command Types: Stack Manipulation, Arithmetic, Heap Access, Flow Control, and I/O
These commands and their parameters consist of whitespace characters: Space, Tab, and LineFeed.

Visit http://compsoc.dur.ac.uk/whitespace/tutorial.html for a Whitespace tutorial.
Visit https://learnxinyminutes.com/docs/brainfuck/ for a Brainfuck tutorial. See bottom of this file to see our modifications to Brainfuck.

BR__NF_CK introduces three new commands that offer an ability to crossover between the two languages.

Crossover: The crossover command tells the interpreter to switch the interpretation of the code to the other language.

• I am coding in the brainfuck environment and want to switch to whitespace:

• • • _[SPACE][SPACE][SPACE][Tab][LF]

• This code increments the data pointer in brainfuck and increments that value in that cell by 3. Then it switches to whitespace and pushes 1 onto the stack. Note how there can be whitespace in the brainfuck code that is not interpreted as whitespace code.

The crossover command is done by using the underscore character: _

The two data structures, whitespace stack and brainfuck array, were independent. But it might be useful for the programmer to communicate between them.

Steal: The steal command reads the value in the inactive language and writes it to the location in the active language.

• If writing in brainfuck, the steal would take whatever is at the top of the stack and write it in the cell currently pointed to by the data pointer.
• If writing in whitespace, the steal would take whatever is at the cell currently pointed to by the data pointer and pushes it onto the stack.

The steal command is done by using the backslash character: \

Giveaway: The giveaway command is the opposite of the steal. It puts the current value into the current location in the other language.

• If writing in brainfuck, the giveaway would take whatever is at the cell currently pointed to by the data pointer and push it onto the stack.
• If writing in whitespace, the giveaway would take whatever is at the top of the stack and write it in the cell currently pointed to by the data pointer.

The giveaway command is done by using the forward slash character: /

Brainfuck modification: There is a slight alteration to the brainfuck language: , is used for single char input and ` is used for single int input. In traditional brainfuck implementations the each cell is the size of a byte. In our implementation, each cell is the size of an int to ensure safe transactions between brainfuck and whitespace data representations. Also, the whitespace language has two input methods read char and read int and the brainfuck language is edited to be consistent. There is a similar alteration for output. '.' is used to output a char, and ! is used to output an int.
Single char input is sometimes used by programs to receive a zero-terminated string of variable length from a user. It is difficult to properly prompt the user for input in these situations by reading in one character at a time, not only because this makes the process of writing in a long string tedious, but also because the user does not have an easy way to type a null character to terminate the input. One may attempt to terminate the input with a newline character instead, but this is not a complete solution because some programs accept the newline character as input. Currently, br__nf_ck reads character input in brainfuck mode from an Input.txt file that can be modified by the user. One possible problem may arise if a program attempts to ask the user for multiple strings of input. Then the same problem of providing a null character is encountered. One possible solution to this that could be implemented in the future is for br__nf_ck to interpret escape sequences in the input.