(Dreg's Fork) Flex & Bison example

A compiler and interpreter of a toy language. Using C++, Flex and Bison.

while.exe program is in this repo ready to use on Windows!

The toy language "While language"

The language is called the While language. Its different variants often serve educational purposes.

Features:

• two types (boolean and natural)
• expressions of these two types
• assignment instruction
• reading/writing from standard input/output
• branching
• looping

Example:

program test_write_natural
    natural n
    natural i
    natural f
    natural t
begin
    f := 0
    t := 3
    for i := f to t do
        write(69)
        write(i)
    done
    read(n)
    while not (n = 0) do
        i := n
        while i > 0 do
            write(n)
            i := i-1
        done
        read(n)
    done
end

See the test/*.ok* files to learn the syntax and semantics of the language.

Building the project

Make sure you have g++, flex, bison and nasm installed. The project was tested with the following versions: g++ 8.3.0 (C++14), flex 2.6.4, bison 3.3.2, nasm 2.14. It might work with other versions as well.

Install deps (Debian based example):

sudo apt-get install g++ flex bison nasm build-essential gcc-multilib libfl-dev

Use these following commands to build the project (including flex+bison files):

make clean
make

WARNING: make clean must be executed first to cleanup all pre-generated flex+bison files

Use the following command to run tests:

make test

Use the following command to cleanup all generated files:

make clean

WARNING: if you are using a 32bit OS just update Makefile with the following commands:

sed -i 's/nasm -f elf32/nasm -felf/g' Makefile
sed -i 's/gcc -m32/gcc/g' Makefile

Building the project without bison+flex installed

Modify Makefile:

sed -i 's/flex /# flex /g' Makefile
sed -i 's/bison /# bison /g' Makefile

Use the following command to build the project without bison+flex installed:

make

(For windows just use mingw32-make.exe)

Don't use make clean, use instead the following command to cleanup all generated files:

make no-flex-bison-clean

Using the interpreter

The following command executes a While program immediately:

./while -i path/to/your/while.program

Example:

echo -e "program dregpoc\nbegin\nwrite(69)\nend" > poc.w
./while -i poc.w

Output (stdout):

69

Using the compiler

The following command compiles a While language program to NASM assembly:

./while -c path/to/your/while.program > output.asm

To further compile the assembly program to an executable

64 bit OS:

nasm -f elf32 output.asm
gcc -m32 output.o io.c -o output

32 bit OS:

nasm -felf output.asm
gcc output.o io.c -o output

To run the executable output:

./output

---

windows powershell example generating assembly program (using stdin as input):

Write-Output "program dreg`nbegin`nwrite(69)`nend" | .\while.exe -c

Output (stdout):

global main
extern write_natural
extern read_natural
extern write_boolean
extern read_boolean

section .bss

section .text
main:
mov eax,69
push eax
call write_natural
add esp,4
xor eax,eax
ret

Compile while output nasm program with nasm+mingw using powershell

Write-Output "program dreg`nbegin`nwrite(69)`nend`n" | .\while.exe -c | % { $_ -replace 'write' , '_write' }  | % { $_ -replace 'read' , '_read' } | % { $_ -replace 'main' , '_main' } | out-file -encoding ascii poc.asm

nasm.exe -f win32 poc.asm

mingw32-gcc.exe poc.obj io.c -o poc.exe

.\poc.exe

69

Changelog

2023 May

From @Kokan 's fork:

• add stdin as input when no file-arg
• add a basic CI github actions (makefile.yml...)
• add tests for elvis operator (?), FOR _ := _ TO _ DO _ DONE loop ...
• flex and bison as optional tools to build the project (uploaded pre-generated files)
• dirty and uncomplete windows support + .exe compiled with mingw (deps static)
• by default->64bit OS compiles/assembles 32bit code (added instructions for 32bit OS)
• merged some PR's from original repo by @devaigergely81
• master to main
• .gitignore, .gitattributes ...
• better README.md
• add changelog, to-do, credits, new license header...
• ...

TO-DO

• more tests (especially for Kokan's work: elvis operator, multiple assignment and "for loop")
• improve CI (more github actions, add more distros...)
• improve Makefile (current version sucks)
• clang-format + clang-tidy
• better doc
• docker
• flex+bison+windows+nasm instructions: https://github.com/lexxmark/winflexbison + https://osdn.net/projects/mingw/ + https://www.nasm.us
• document internals: how nasm code is generated, asm snippets, how write_natural is linked ...
• better windows support: Makefile (make clean, tests, ...), compilation with nasm, ....
• ...
• http://gnuwin32.sourceforge.net/packages/flex.htm
• http://gnuwin32.sourceforge.net/packages/bison.htm

License

This software is licensed under the MIT license. See the LICENSE file for details.

Credits

• original repo by Gergely Dévai ( @devaigergely81 ): https://github.com/devaigergely81/flex-bison-example
• fork by Kókai Péter ( @Kokan ): https://github.com/Kokan/flex-bison-example