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jorenheit / brainfix

Compiler that translates C-style language Brainfix to Brainfuck

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Brainfix

BrainFix is a compiler/language that takes a C-style language (although the syntax slowly evolved to something very close to Javascript for some reason) and compiles this into BrainF*ck, an esoteric programming language consisting of only 8 operations.

To run the resulting Brainf*ck code, you can use any (third party) BrainF*ck interpreter. However, this project includes its own interpreter (bfint) which supports different cell-sizes and random number generation, working nicely in tandem with the bfx compiler. Both bfx and bfint will be built by the included Makefile; see instructions below.

Building

To build the project, simply cd into the root folder of this project and run make:

git clone https://github.com/jorenheit/brainfix
cd brainfix
make

To install the resulting binaries and standard library files to your PATH, run as root:

make install

By default, this will copy the binaries (bfx and bfint) to /usr/local/bin and the library files to /usr/include/bfx. These directories can be changed by editing the first couple of lines in the Makefile.

If for some reason you want to change the grammar specification, you can let bisonc++ and flexc++ (see below) regenerate the sourcecode for the scanner (file: lexer) and parser (file: grammar) by running

make regenerate

To remove all object files, run

make clean

To undo all actions performed by make install, run as root

make uninstall

bfint and ncurses

By default, the bfint with depend on the ncurses libraries to be linked against, in order to support gaming-mode (see below for details). If ncurses is not installed on your system and you wish to not install it, please edit the Makefile and set GAMING_MODE_AVAILABLE=0.

Bisonc++ and Flexc++

The lexical scanner and parser that are used to parse the Brainfix language are generated by Bisonc++ and Flexc++ (not to be confused with bison++ and flex++). This software is readily available in the Debian repositories, but not necessarily needed to build this project. The sourcefiles generated by these programs, based on the current grammar and lexer specifications, are included in the source-folder.

Usage

Using the bfx executable

Building the project results will produce the compiler executable bfx. The syntax for invoking the compiler can be inspected by running bfx -h:

Usage: bfx [options] <target(.bfx)>
Options:
-h, --help          Display this text.
-t, --type [Type]   Specify the number of bytes per BF-cell, where [Type] is one of
                    int8, int16 and int32 (int8 by default).
-I [path to folder] Specify additional include-path.
                      This option may appear multiple times to specify multiple folders.
-O0                 Do NOT do any constant expression evaluation.
-O1                 Do constant expression evaluation (default).
--max-unroll-iterations [N]
                    Specify the maximum number of loop-iterations that will be unrolled.
                      Defaults to 20.
--random            Enable random number generation (generates the ?-symbol).
                      Your interpreter must support this extension!
--profile [file]    Write the memory profile to a file. In this file, the number of visits
                      to each of the cells is listed.
--no-bcr            Disable break/continue/return statements for more compact output.
--no-multiple-inclusion-warning
                    Do not warn when a file is included more than once, or when files
                      with duplicate names are included.
--no-assert-warning
                    Do not warn when static_assert is used in non-constant context.
-o [file, stdout]   Specify the output stream/file (default stdout).

Example: bfx -o program.bf -O1 -I ~/my_bfx_project -t int16 program.bfx

Using the bfint executable

To run the resulting BF, call the included interpreter or any other utility that was designed to run or compile BF. When using the included bfint interpreter, its syntax can be inspected by running bfint -h:

$ bfint -h
Usage: ./bfint [options] <target(.bf)>
Options:
-h, --help          Display this text.
-t, --type [Type]   Specify the number of bytes per BF-cell, where [Type] is one of
                    int8, int16 and int32 (int8 by default).
-n [N]              Specify the number of cells (30,000 by default).
-o [file, stdout]   Specify the output stream (defaults to stdout).

--gaming            Enable gaming-mode.
--gaming-help       Display additional information about gaming-mode.
--random            Enable Random Brainf*ck extension (support ?-symbol)
--rand-max [N]      Specifiy maximum value returned by RNG.
                      Defaults to maximum supported value of cell-type
--no-random-warning Don't display a warning when ? occurs without running --random.

Example: ./bfint --random -t int16 -o output.txt program.bf

The type of a BrainF*ck cell

The type of the BF cell that is assumed during compilation with bfx can be specified using the -t option and will specify the size of the integers on the BF tape. By default, this is a single byte (8-bits). Other options are int16 and int32. All generated BF-algorithms work with any of these architectures, so changing the type will not result in different BF-code. It will, however, allow the compiler to issue a warning if numbers are used throughout the program that exceed the maximum value of a cell. The same flag can be specified to bfint. This will change the size of the integers that the interpreter is operating on. For example, executing the + operation on a cell with value 255 will result in overflow (and wrap around to 0) when the interpreter is invoked with -t int8 but not when it's invoked with -t int16.

Constant Evaluation (O0 vs O1)

By default (option -O1), the compiler will perform as many calculations as it can at compile-time. For instance, consider the following expression:

let n = 3 + 4;

The value 7 will be stored internally, but no BF-code will be generated because the value of n is not used to do anything. However, when the compiler is called with the O0-flag, every operation is translated directly to BF-code. In case of the example above, this will result in the following operations:

  1. Create a cell containing the number 3.
  2. Create a cell containing the number 4.
  3. Perform the addition algorithm on these cells.

For obvious reasons, running in O0-mode will lead to significantly larger output. For example, the 'Hello World'-example below, when run in O0-mode, results in a total of approximately 12,000 BF-operations. In the default O1-mode, it's less than 1,200 operations.

Example: Hello World

Every programming language tutorial starts with a "Hello, World!" program of some sort. This is no exception:

// File: hello.bfx
include "std.bfx"

function main()
{
    println("Hello, World!");
}

Comments

The program starts with an end-of-line comment (C-comment blocks between /* and */ are also allowed) and then includes the standard-library which is included with this project. This exposes (among other things, see below) some basic IO-facilities the sourcefile.

main

Next, the main-function is defined. Every valid BFX-program should contain a main function which takes no arguments and does not return anything. The order in which the functions are defined in a BFX-file does not matter; the compiler will always try to find main and use this as the entrypoint.

Compiling

In main(), the function println() from the IO library is called to print the argument and a newline to the console. If you've run make install, these files should be in a folder known to the compiler. If not, you should point the compiler to the folder containing the stdlib-files using the -I /path/to/std option.

$ bfx -o hello.bf hello.bfx
$ bfint hello.bf
Hello, World!

Target Architecture

The compiler targets the canonical BrainF*ck machine, where cells are unsigned integers of the type specified as the argument to the -t flag. At the start of the program, it is assumed that all cells are zero-initialized and the pointer is pointing at cell 0. Furthermore, it is assumed that the tape-size is, for all intents and purposes, infinitely long. The produced BF consists of only the 8 classic BF-commands and an optional RNG command, as per the Random Brainfix extension (to allow for simple games).

Command Effect
> Move pointer to the right.
< Move pointer to the left.
+ Increase value pointed to by 1.
- Decrease value pointed to by 1.
[ If current value is nonzero, continue. Otherwise, skip to matching ]
] If current value is zero, continue. Otherwise, go back to matching [
. Output current byte to stdout
, Read byte from stdin and store it in the current cell
? Spawn a random number in the current cell (non-standard!)

Gaming Mode

If bfint was linked against Ncurses (Makefile: GAMING_MODE_AVAILABLE=1), it will have the option to run in gaming-mode using the --gaming option. When running in gaming-mode, all input is processed immediately, rather than having to press enter before the input is accepted. This allows you to run simple games that respond to keypresses, like the included snake example (bfx_examples/snake.bfx). When no keypress is buffered when a , is encountered, a 0 will be stored in the current cell.

In order to achieve non-blocking IO, not only input but also all output will be handled by the Ncurses library. ANSI escape sequences, which can be used to tell your terminal to move the cursor, clear parts of the screen or even change the text-color, are not supported by ncurses. Therefore, bfint will try to parse some common ANSI sequences and call the appropriate ncurses library functions accordingly. Currently supported sequences include:

ANSI Sequence Effect
ESC[nA Move the cursor up n lines.
ESC[nB Move the cursor down n lines.
ESC[nC Move the cursor right n steps.
ESC[nD Move the cursor left n steps (erasing present characters).
ESC[n;mH Move the cursor to row n, column m.
ESC[H Move the cursor to the top-left of the screen.
ESC[nK n = 0: clear from cursor to end-of-line.
n = 1: clear from cursor to start-of-line.
n = 2: clear the entire line.
ESC[nJ n = 0: clear from cursor to bottom of screen.
n = 1: clear all lines above cursor, including current line.
n = 2: clear entire screen.

Language

Functions

A BrainFix program consists of a series of functions (one of which is called main()). Apart from global variable declarations, const declarations, user-defined types (structs) and file inclusion (more on those later), no other syntax is allowed at global scope. In other words: BF code is only generated in function-bodies.

A function without a return-value is defined like we saw in the 'Hello World' example and may take any number of parameters. For example:

function foo(x, y, z)
{
    // body
}

When the function has a return-value, the syntax becomes:

function ret = bar(x, y, z)
{
    // body --> must contain instantiation of 'ret' !
}

It does not matter where a function is defined with respect to the call:

function foo()
{
    let x = 31;
    let y = 38;

		let nice = bar(x, y); // works, even if bar is defined below
}

function z = bar(x, y)
{
    let z = x + y; // return variable is instantiated here
}

Function Overloading

Functions can be overloaded on their number of arguments (not on return-value). This allows you to define multiple functions with the same name. In the example below, overloading is used to implement a default argument.

function bestNumber(x)
{
    printd(x);
    println(" is the best number.");
}

function bestNumber()
{
    bestNumber(42);
}

function main()
{
    bestNumber();
    bestNumber(69);
}

Value and Reference Semantics

By default, all arguments are passed by value to a function: every argument is copied into the local scope of the function. Modifications to the arguments will therefore have no effect on the corresponding variables in the calling scope.

function foo()
{
    let x = 2;
    bar(x);

    // x == 2, still
}

function bar(x)
{
    ++x;
}

However, BrainFix supports reference semantics as well. Parameters prefixed by & (like in C++) are passed by reference to the function. This will prevent the copy from taking place and will therefore be faster than passing it by value. However, it also introduces the possibility of subtle bugs, which is why it's not the default mode of operation.

function foo()
{
    let x = 2;
    bar(x);

    // x == 3 now
}

function bar(&x)
{
    ++x;
}

Recursion

Unfortunately, recursion is not allowed in BrainFix. Most compilers implement function calls as jumps. However, this is not possible in BF code because there is no JMP instruction that allows us to jump to arbitrary places in the code. It should be possible in principle, but would be very hard to implement (and would probably require a lot more memory to accomodate the algorithms that could make it happen). Therefore, the compiler will throw an error when recursion is detected.

Variable Declarations

New variables are declared using the let keyword and can from that point on only be accessed in the same scope; this includes the scope of if, for and while statements. At the declaration, the size (or type, see below) of the variable can be specified using square brackets. Variables declared without a size-specifier are allocated as having size 1. It's also possible to let the compiler deduce the size of the variable by adding empty brackets [] to the declaration. In this case, the variable must be initialized in the same statement in order for the compiler to know its size. After the declaration, only same-sized variables can be assigned to eachother, in which case the elements of the right-hand-side will be copied into the corresponding left-hand-side elements. There is one exception to this rule: an single value (size 1) can be assigned to an array as a means to initialize or refill the entire array with this value.

function main()
{
    let x;                // size 1, not initialized
    let y = 2;            // size 1, initialized to 2
    let [10] array1;      // array of size 10, not initialized
    let [] str = "Hello"; // the size of str is deduced as 5 and initialized to "Hello"

    let [y] array2;       // ERROR: size of the array must be a number or const
    let [10] str2 = str;  // ERROR: size mismatch in assignment
    let [10] str3 = '0';  // OK: str3 is now a string of ten '0'-characters
}

References (or alias-variables)

Variables can also be declared as references (or aliases). The newly declared variable will from that point on be synonymous to the original variable, which can therefore be changed through the alias.

function main()
{
    let x = 42;
    let &y = x;

    y = 69;
    printd(x); // will print 69
}

It's possible to alias entire arrays and single array-elements. The latter can only be done when the index is known at compiletime. When the index cannot be evaluated at compiletime, or when the compiler is in -O0-mode, the contents of the cell are copied to a temporary cell. As a general rule, it's forbidden to alias temporary objects, so an error will occur when trying to alias an array-element for which the address is not known. Furtermore, even when the index is known, trying to alias the first element (index 0) might lead to some unintuitive behavior: see the section below on deducing the size of arr[0].

Initializing Variables

In the example above, we see how a string is used to initialize an array-variable. Other ways to initialize arrays all involve the # symbol to indicate an array-literal. In each of these cases, the size-specification can be empty, as the compiler is able to figure out the resulting size from its initializer.

function main()
{
    let v1 = 1;
    let v2 = 2;
    let zVal = 42;

    let []x = #{v1, v2, 3, 4, 5}; // initializer-list
    let []y = #[5];               // 5 elements, all initialized to 0
    let []z = #[5, zVal];         // 5 elements, all initialized to 42

    let [zVal] arr;               // ERROR: size-specifier is not const
}

Size specifications must be known at compiletime; see the section on the const keyword below on how to define named compile-time constants.

Caution: Deducing the size of arr[0]

To the compiler, the expressions arr and arr[0] are completely identical, because they both return the exact same address. This leads to complications when assigning the value of arr[0] to a new variable for which the size was not specified by the programmer, or when this element is being aliased.

    let [] arr = #{1, 2, 3, 4, 5}; // sizeof(arr) == 5

    let [] x = arr[2]; // OK, sizeof(x) == sizeof(arr[2]) == 1
    let [] y = arr[0]; // Whoops, sizeof(y) == sizeof(arr) == 5

    let &arr2 = arr[0]; // Whoops, arr2 refers to the entire array
    let &z = arr[2];    // OK: z refers to 3rd element of arr

Structs

In addition to declaring a variable by specifying its size, its type can be specified using the struct keyword and a previously defined struct-identifier. The definition of this struct must appear somewhere at global scope and can contain fields of any type, including arrays and other user defined types.

struct Vec3
{
    x, y, z;
}; // semicolon is optional

struct Particle
{
    [struct Vec3] pos, [struct Vec3] vel; // nested structs
    id;                                   // fields specified over multiple lines
};

function print_vec3(&v)
{
    printc('(');
    printd(v.x); prints(", ");
    printd(v.y); prints(", ");
    printd(v.z); prints(")\n");
}

function main()
{
    let [struct Particle] p;

    p.id = 42;

    p.pos.x = 1;
    p.pos.y = 2;
    p.pos.z = 3;

    p.vel = Vec3{4, 5, 6};  // initializing using an anonymous Vec3 instance

    print_vec3(p.pos);
    print_vec3(p.vel);
}

Numbers

Only positive integers are supported; the compiler will throw an error on the use of the unary minus sign. A warning is issued when the program contains numbers that exceed the range of the specified type (e.g. 255 for the default int8 type).

Indexing

Once a variable is declared as an array, it can be indexed using the familiar index-operator []. Elements can be both accessed and changed using this operator. When the index to the array can be resolved at compile-time, the compiler will check if it is within bounds. Otherwise, it's up to the programmer to make sure the index is within the size of the indexed variable.

function main()
{
    let [] arr = #(42, 69, 123);

    ++arr[0];     // 42  -> 43
    --arr[1];     // 69  -> 68
    arr[2] = 0;   // 123 -> 0

    arr[5] = 'x'; // Error will be reported!

    let n = scand();
    arr[n] = 'y'; // Anything may happen ...
}

Passing array-elements by reference

Operating on arrays using the index-operator usually works as expected. However, when an array-element is accessed through the index-operator (without operating on it) and passed to a function, the result of this expression might be temporary copy of the actual element, depending on whether the index was resolved at compile-time. If it was, the behaviour is as expected and an actual reference to the indexed element will be passed to the function. If however, the index cannot be resolved at compile-time, a temporary value containing a copy of the element is returned by the index operator. This is because the position of the BF-pointer has to be known at all times, even when the index is a runtime variable (for example determined by user-input). This leads to different semantics in both cases, which could be confusing. Consider the following example to illustrate the two cases:

function modify(&x)
{
    ++x;
}

function main()
{
    let [5] arr = #{1, 2, 3, 4, 5};

    let n = 3;         // known at compiletime
    let m = scand();   // known at runtime

    ++arr[m];          // Works, even though m is a runtime variable

    modify(arr[n]);    // Fine: modified the 3rd element in-place
    modify(arr[m]);    // Fail: did not modify arr at all
}

To be safe, one should always pass the array and its index as seperate arguments to an element-modifying function, unless you're sure that it will only be called in a constant evaluation context. For example:

function modify(&arr, &idx)
{
    ++arr[idx];
}

function main()
{
    let [5] arr = #{1, 2, 3, 4, 5};

    let m = scand();   // known at runtime
    modify(arr, m);    // works now
}

sizeof()

The sizeof() operator (it's not really a function, as it's a compiler intrinsic and not defined in terms of the BrainFix language itself) returns the size of a variable and can be used, for example, to loop over an array (more on control-flow in the relevant sections below).

function looper(arr)
{
    for (let i = 0; i != sizeof(arr); ++i)
        printd(arr[i]);
}

Constants

BrainFix provides a simple way to define constants in your program, using the const keyword. const declarations can only appear at global scope. Throughout the program, occurrences of the variable are replaced at compiletime by the literal value they've been assigned. This means that const variables can be used as array-sizes (which is their most common usecase):

const SIZE = 10;

function main()
{
    let [] arr1 = #[SIZE, 42];
    let [] arr2 = #[SIZE, 69];

    arr1 = arr2; // guaranteed to work, sizes will always match
}

Global Variables

It's also possible to define runtime variables at global scope, using the global keyword. A global variable cannot be initialized in this declaration, so it's common to define an initializing function that's called from main.

include "std.bfx"

global x, y;      // single global variables
global [5]vec;    // global array of 5 cells

struct S
{
    x, y;
};

global [struct S] s;

function init()
{
    x = 42;
    y = 69;
    s = S{10, 20};
}

function main()
{
    init();

    printd(x);   endl();
    printd(y);   endl();
    printd(s.x); endl();
    printd(s.y); endl();
}

Operators

The following operators are supported by BrainFix:

Operator Description
++ post- and pre-increment
-- post- and pre-decrement
+ add
- subtract
* multiply
/ divide
% modulo
^ power
+= add to left-hand-side (lhs), returns lhs
-= subtract from lhs, returns lhs
*= multiply lhs by rhs, returns lhs
/= divide lhs by rhs, returns lhs
%= calculate the remainder of (lhs / rhs) and assign it to lhs
/=% divide lhs by rhs; returns the remainder
%=/ assign the remainder to lhs; returns the result of the division
^= raises lhs to power rhs; returns the result
&& logical AND
|| logical OR
! (unary) logical NOT
== equal to
!= not equal to
< less than
> greater than
<= less than or equal to
>= greater than or equal to

Logical Shortcircuiting

Unline in many other languages, the logical operators && and || will not short-circuit, which means that it's guaranteed that both operands will be evaluated and their side-effects will be taking place.

function x = foo()
{
    println("Hello from foo");
    let x = false;
}

function x = bar()
{
    println("Hello from bar");
    let x = true;
}

function main()
{
    let x = foo() && bar(); // bar will be called, even though foo() already returned false;
    let y = bar() || foo(); // foo will be called, even though bar() already returned true;
}

The div-mod and mod-div operators

Most of these operators are commonplace and use well known notation. The exception might be the div-mod and mod-div operators, which were added as a small optimizing feature. The BF-algorithm that is implemented to execute a division, calculates the remainder in the process. These operators reflect this fact, and let you collect both results in a single operation.

function divModExample()
{
    let x = 42;
    let y = 5;

    let z = (x /=% y);

    // x -> x / y (8) and
    // z -> x % y (2)
}

function modDivExample()
{
    let x = 42;
    let y = 5;

    let z = (x %=/ y);

    // x -> x % y (2) and
    // z -> x / y (8)
}

Flow

There are 4 ways to control flow in a BrainFix-program: if (-else), switch, for and while. Each of these uses similar syntax as to what we're familiar with from other C-like programming languages. Below we will see an example for each of these statements.

C-style for-loops

The first kind of for-loop has the classic C-syntax we all know and love. You specify the initialization-expression (cannot currently be an empty expression), the loop-condition and the increment-statement:

// Single statement, no curly braces necessary
for (let i = 0; i != 10; ++i)
    printd(i);

// Compound statement
for (let i = 0; i != 10; ++i)
{
    let j = i + 10;
    printd(j);
    endl();
}

Range-based for-loops

It is common to iterate over the elements of an array. In some cases, where you don't need the index of the elements as an accessible variable, you can specify the array you need to iterate over without using an index. In the example below, each element of the array will be copied into the variable x:

let [] array = #{1, 2, 3, 4, 5};

for (let x: array)
{
    printd(x);
    endl();
}

The loop-variable can also be declared as a reference to modify the array-elements in-place. This only works for loops that will be unrolled (see the section on loop-unrolling below).

let [] array = #{1, 2, 3, 4, 5};

for (let &x: array)
    ++x;  // increment all elements in-place

While-loops

The while-loop also has syntax familiar from other C-style languages. It needs no further introduction:

let [] str = "Hello World";
let i = 0;
while (str[i] != 'W')
{
    printc(str[i++]);
}
endl();

If-statements

The if-syntax is again identical to that of C. It supports arbitrarily long if-else ladders:

let x = scand();
if (x < 10)
   println("Small");
else if (x < 20)
     println("Medium");
else
{
    println("Large!");
}

Switch Statements

In BrainFix, a switch statement is simply a syntactic alternative to an if-else ladder. Most compiled languages like C and C++ will generate code that jumps to the appropriate case-label (which therefore has to be constant expression), which in many cases is faster than the equivalent if-else ladder. In BrainF*ck, this is difficult to implement due to the lack of jump-instructions.

Each label has to be followed by either a single or compound statement, of which only the body of the first match will be executed (it's not possible to 'fall through' cases). The break and continue control statements will be seen as local to the enclosing scope around the switch (like any old if-statement). A break statement is therefore not required in the body of a case and in fact will probably have different semantics compared to what you're used to. Beware! If you need to skip part of the switch-body, consider using continue instead. For more information on break, continue and return, see below.

while (true)
{
    prints("Enter a number 0-3, or 9 to quit: ");
    let x = scand();
    switch (x) {
        case 0: println("Zero");
        case 1: println("One");
        case 2: println("Two");
        case 3: println("Three");
        case 9:
        {
            println("Quitting ...");
            break; // will break out of the while!
        }
        default: println("Not sure ...");
    }
}

Unlike in C, case labels in Brainfix do not have to be constant expressions, which allows us to write code like this (although it might not be recommended):

let x = scand();
let y = scand();

switch (x)
{
    case y:  println("Same");
    default: println("Different");
}

Preventing Loop Unrolling with for* and while*

Within a runtime-evaluated loop, the compiler can't make any assumptions about the values of each of the variables, so it has to output BF-algorithms for each of the operations in the body of the loop. Because of this, loops generally yield great amounts of BF code. To reduce the size of the output, the compiler will by default try to unroll loops by evaluating the body and condition for as long as it can. When the loop can't be fully unrolled (because the stop-condition can only be known at runtime) or the number of iterations exceeds its maximum (20 by default, or otherwise set through --max-unroll-iterations), it will fall back on generating code for executing the loop at runtime.

However, loop-unrolling can take a long time, resulting in long compilation times for loops with large bodies or many iterations. Especially in the latter case, it can take some time before the compiler realizes it shouldn't unroll the loop at all (since it has to evaluate the body 20 times before coming to this conclusion). To indicate to the compiler that it shouldn't attempt to unroll the loop, we can use for* and while* instead. For range-based for-loops, the compiler can predetermine the number of iterations; this cannot be changed in the body of the loop. Therefore, it can decide beforehand whether or not to unroll the loop without any compilation time-penalty. Using for* will overrule the decision of the compiler and will force it to not unroll, but this will not result in faster compilation times.

function main()
{
    // The compiler will try to unroll this, even though we can see
    // that it will take 100 iterations and will therefore not be
    // unrolled (assuming the default maximum of 20 iterations).
    for (let i = 0; i != 100; ++i)
    {
        printd(i);
        endl();
    }

    // Use for* instead: same resulting BF-code, faster compilation.
    for* (let i = 0; i != 100; ++i)
    {
        printd(i);
        endl();
    }

    // Ranged-for* will not unroll, but this won't result in faster compilation.
    let [] arr = #{1, 2, 3, 4};
    for* (let x: arr)
    {
        printd(x)
        endl();
    }

    // Will produce a warning: runtime-loops cannot be iterated by reference:
    for* (let &x: arr)
        ++x;
}

Break, Continue and Return

By default, the familiar break, continue and return statements are supported to control the flow of your program. In contrast to many other languages, these statements are supported in any context; not necessarily in loops.

break

Will force flow to break out of the enclosing scope (skipping all statements until the closing brace). When issued at function-scope-level, it will return from the function.

for (let i = 0; i != 10; ++i)
{
    if (i == 5)
       break;
    printd(i);
}
// Prints "01234"
continue

Like break, a continue statement will skip all statements until the closing brace. However, at this point flow will restore and (if issued in a loop-context) the next iteration will be executed as normal. Again, if continue is used at function-scope-level, it will simply return from the function.

for (let i = 0; i != 10; ++i)
{
    printd(i);
    if (i > 5)
       continue;
    printd(i);
}
// Prints "0011223344556789"
return

At any scope-level, return will immediately return from the enclosing function-scope. If the function returns a value, it needs to be declared (and initialized, probably) before this point. Beware that it's therefore not possible to declare the return-value at the scope of the return-statement; it must be declared at function-scope.

function x = get()
{
    let x;
    while (true)
    {
        // let x = scand(); --> x not declared at function-scope
        x = scand();
        if (x > 10)
            return;
    }
}
Compiler option: --no-bcr

Because BF does not support arbitrary jumps in code, the break, continue and return directives (bcr) have been implemented through a pair of flags that need to be checked continuously in order to determine whether a statement needs to be executed. Effectively, this means that every line of code will be wrapped in an if-statement. Especially when compiling without constant-evaluation (-O0) or when constant evaluation is not possible due to user-input dependencies, this will lead to a lot of code-bloat and therefore very large BF-output. The compiler-flag --no-bcr will disable support for break, continue and return; using these directives will in that case produce a compiler error.

File Inclusion

The compiler accepts only 1 sourcefile, but the include keyword can be used to organize your code among different files. Even though the inner workings are not exactly the same as the C-preprocessor, the semantics pretty much are. When an include directive is encountered, the lexical scanner is simply redirected to that file and continues scanning the original file when it has finished scanning the included one.

Duplicate and Circular Inclusions

Files, or files with the same filename, can only be included once. When a multiple inclusion (which could be circular) is detected, a warning is issued. Two files with the same filename, even when they are different files in different folders and with different contents, will be treated as the same file: only the file that was first encountered is parsed and a warning will be issued. This warning can be suppressed with the --no-multiple-inclusion-warning flag.

Custom Error Messages

Generating runtime error messages usually produce lots of additional BF output. In many cases, you might want to perform checks which can be done at compiletime. In this case, you can use the compiler directive static_assert(check, msg), which takes any (constant) expression and a message to be displayed as an error message. The compiler will report this error when the check fails:

function copy(&dest, &src)
{
    static_assert(sizeof(dest) >= sizeof(src),
                  "Destination buffer is too small.");

    // ...
}

Because this is a compile-time check, static_assert can only be used when compiling with -O1. If used in a non-constant context (when compiling with -O0 or in a runtime-evaluated for-loop for example), a warning will be issued and the assertion will be ignored. This warning can be disabled with the --no-assert-warning option.

Side Effects of static_assert

The check-expression of a static assertion will never have any side effects. Internally, static_assert will reset the state of the program to the state prior to the assertion.

function x = fun(&x)
{
    ++x;
}

function main()
{
    let x = 0;

    static_assert(fun(x) == 1, "This is weird!");
    printd(x); // prints 0
    endl();
    
    fun(x);
    printd(x); // prints 1
    endl();
}

Standard Library

The standard library provides some useful functions in two categories: IO and mathematics. Below is a list of provided functions that you can use to make your programs interactive and mathematical. Also, in the "stdbool.bfx" headerfile, the constants true and false are defined to 1 and 0 respectively.

IO

All functions below are defined in BFX_INCLUDE/stdio.bfx:

function description
printc(x) Print x as ASCII character
printd(x) Print x as decimal (at most 3 digits)
printd_4(x) Print x as decimal (at most 4 digits)
prints(str) Print string (stop at \0 or end of the string)
println(str) Same as prints() but including newline
print_vec(v) Print formatted vector, including newline: (v1, v2, v3, ..., vN)
endl() Print a newline (same as printc('\n'))
scanc() Read a single byte from stdin
scand() Read at most 3 bytes from stdin and convert to decimal
scand_4() Read at most 4 bytes from stdin and convert to decimal
scans(buf) Read string from stdin. sizeof(buf) determines maximum number of bytes to read
to_int(str) Converts string to int (at most 3 digits)
to_int_4(str) Converts string to int (at most 4 digits)
to_string(x) Converts int to string (at most 3 digits)
to_string_4(x) Converts int to string (at most 4 digits)
to_binary_str(x) Returns binary representation of x as a string
to_hex_str(x) Returns hexadecimal representation of x as a string
Big Numbers

On the default architecture, where the cells are only 1 byte long, values can never grow beyond 255. It is therefore sufficient to assume that number will never grow beyond 3 digits. However, when the target architecture contains larger cells, the functions suffixed with _4 can be used to extend some facilities to 4 digits. Printing and scanning even larger digits is also possible, but functions to this end are not provided by the standard library for the simple reason that these functions would be terribly slow and impractical.

Cursor and Screen Manipulation

The functions below are also defined in stdio.bfx and can be used on ANSI-compatible terminals to move the cursor or clear (parts of) the screen. This can be used to print to the same region of the screen multiple times, allowing for better ascii-graphics. The ANSI sequences used to implement these functions are all supported by bfint's gaming mode, so programs using these functions can be run both with and without --gaming enabled.

function description
cursor_left(n) Move cursor left by n (default = 1)
cursor_right(n) Move cursor right by n (default = 1)
cursor_up(n) Move cursor up by n (default = 1)
cursor_down(n) Move cursor down by n (default = 1)
cursor_home() Move cursor to top-left of the screen
cursor_to(line, column) Move cursor to given position
clear_screen() Clear the entire screen
clear_line() Clear the current line

Math

All functions below are defined in BFX_INCLUDE/stdmath.bfx:

function description
sqrt(x) Calculate the square root of x, rounded down
factorial(n) Calculate n! (overflows for n > 5)
min(x,y) Returns the minimum of x and y
max(x,y) Returns the maximum of x and y
to_binary_array(x) Returns 8-bit binary representation of x as array of 0's and 1's
from_binary_array(x) Takes a binary array and converts it back to 8-bit integer
bit8_or(x, y) Returns bitwise OR of x and y (8-bit)
bit8_and(x, y) Returns bitwise AND of x and y (8-bit)
bit8_xor(x, y) Returns bitwise XOR of x and y (8-bit)
bit8_shift_left(x, n) Shift the binary representation of x by n bits to the left.
bit8_shift_right(x, n) Shift the binary representation of x by n bits to the right.
rand() Generate random number (see below).

Each of the functions above returns the resulting value: their arguments are never modified, even if they are taken by reference (for optimization purposes).

Strings

All functions below are defined in BFX_INCLUDE/stdstring.bfx:

function description
strcpy(dest, str) Copies entire string's contents to array. Returns number of copies elements.
strlen(str) Returns length of the string, up to terminating 0.
strcmp(dest, str) Copies entire string's contents to array. Returns 0 (unequal) or 1 (equal).

Pseudorandom Numbers

To generate random numbers, BrainFix makes use of the Random Brainfix extension, where a ? symbol tells the interpreter to generate a random number. The way this random number is generated is therefore fully up to the interpreter itself and cannot even be seeded from within BrainFix. If the rand()-function is used in a program that is compiled without the --random option, a warning will be issued and compilation will proceed as normal. The included interpreter supports this extension (if the --random flag is passed in to bfint) and will generate a random number uniformly in the range of possible cell-values (0-255 in the single byte case), or up to rand-max if this was provided using the --rand-max option. It is up to the programmer to manipulate the result of rand() into the desired range. A common way to do this is by using the modulo-operator as in the example below.

include "std.bfx"

function main()
{
    for* (let i = 0; i != 20; ++i)
    {
        switch(rand() % 3)
        {
            case 0: println("ROCK!");
            case 1: println("PAPER!");
            case 2: println("SCISSORS!");
        }
    }
}
Rand-Max

As mentioned briefly above, the maximum value for the RNG can be specified using the --rand-max option. This is particularly useful when running bfint in int16-mode when the RNG enabled, which would by default generate very large numbers. These numbers are hard to deal with in BF, causing the resulting program to perform very poorly. It's often not needed to generate random numbers in this range, which is why the maximum can be specified, e.g.

$ bfint --random --rand-max 255 --type int16 --gaming snake.bf

In this example the BF-cells can hold 16-bit integers, but the RNG will only return values up to 255: the best of both worlds!

Profiling

During compilation, the compiler keeps track the number of move-instructions to each of the allocated memory cells. This memory-profile can be saved to a file with the --profile option. The output file reports the settings used for compilation, the resulting number of BF-operations and required cells, followed by a list of cells and the number of times a move to this address was generated. This will not necessarily be the same as the number of visits to this cell at runtime, because at runtime cells may be visited repeatedly in a loop.

$ bfx --no-bcr --profile prof.txt -o sieve.bf bfx_examples/sieve.bfx
$ head -n 20 prof.txt
Profile for bfx_examples/sieve.bfx:
    cell-type:        int8
    optimization:     O1
    bcr:              disabled
    max unroll:       20
    random extension: disabled

Number of BF operations generated: 233505
Number of cells required:          1201

+---------+---------+
| address | #visits |
+---------+---------+
0: 39
1: 29
2: 8
3: 8
4: 12
5: 10
6: 13

Unit Testing

Brainfix supports unit-testing blocks, which tell the bfint interpreter what output is to be expected at given input (if any). Tests are defined in test-blocks, surrounded by @start_test <test-name> and @end_test respectively. Within a test-block, multiple test-cases can be defined using input and expect:

include "std.bfx"

function main()
{
    let x = scand();
    printd(++x);
    endl();
}

@start_test <increment>

<single_digit>
```input
4
```

```expect
5
```

<double_digits>

```input
41
```

```expect
42
```

<triple_digits>

```input
123
```

```expect
124
```

@end_test

When the bfx file is compiled using the --test flag, it will generate two files for each of the tests, containing the inputs and expected outputs respectively, and will store these filenames to the file passed to the --test flag. Subsequently, bfint can be run with the --test option to use the output generated by bfx to compare the inputs and expected outputs. For example, when the example above is stored in a file named increment.bfx:


$ bfx --test increment.test -o increment.bf increment.bfx
$ bfint --test increment.test increment.bf
<increment::single_digit> PASS
<increment::double_digits> PASS
<increment::triple_digits> PASS

Contents of input/expect

Every character in the input and expect-blocks are taken at their literal value, including spaces, newlines and tabs. If you expect non-printable (typable) characters, special characters \n, \t and \0 can be used and literal integers (in ASCII range) can be escaped with ${}. A backslash \ at the end of a line will cause the terminating newline to be ignored.

include "std.bfx"

function main()
{
    let x = scand();
    let newline = scand();

    printc(28);
    printd(++x);
    if (newline)
       endl();
}

@start_test <increment>

<newline>
```input
3
1
```

```expect
${28}4
```

<no_newline>
```input
3
0
```

```expect
${28}4\
```

@end_test

Programs without input

When a program does not depend on input, it's possible to either define an empty input-sequence or omit the input-sequence entirely:

include "std.bfx"

function main()
{
    println("Hello World");
}

@start_test <println>

<hello1>
```expect
Hello World
```

@end_test

Failing tests

If a test should fail, bfint will report both the expect string and actual output. Non-printable characters, including newlines, will be printed as a dot .. For example, when the backslash in the final expect-block of the increment-example above is omitted, bfint will report the following:

<increment::newline> PASS
<increment::no_newline> FAIL
	Expected: ".4."
	Got:      ".4"

About

Compiler that translates C-style language Brainfix to Brainfuck

License:MIT License

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