half

half is an extremely simple language.

the original spec, cloned here:

Half (interpreter/translator in Windows Batch)

I don't know why I'm answering so many puzzles in windows batch, for some sick reason I think I'm enjoying it :P Anyways, this is similar to something I worked on for fun a while ago, a basic language that's translated to windows batch by a script that is also written in windows batch. It's not particularly amazing, but it works.

99 Bottles of Beer

# Initialize variables
bottles ~ 99
# You can't directly compare a literal value
zero ~ 0

# This makes a point 'loop' that can be jumped to or used as a subroutine
mark loop
    write $ bottles
# You only need quotes when you have leading or trailing spaces
    print ~ " bottles of beer on the wall,"
    write $ bottles
    print ~ " bottles of beer."
    print ~ Take one down and pass it around,
    bottles @ bottles-1
    if
    bottles equ zero
        jump none
    endif
    write $ bottles
    print ~ " bottles of beer on the wall."
    print ~
jump loop

mark none
    print ~ no more bottles of beer on the wall.
    print ~
    print ~ No more bottles of beer on the wall,
    print ~ No more bottles of beer.
    print ~ Go to the store and buy some more,
    print ~ 99 bottles of beer on the wall.

Syntax

Only three tokens are recognized on each line, separated by spaces.

# is a comment.

In most cases where a value is needed, a $ in the second token signifies that the third should be treated as a variable name, whereas a ~ denotes a literal value. General instructions take the form <instruction> [$~] <name>. Setting a variable takes the same form, but is implemented whenever is not recognized.

Defined commands:

print and write both write output, but write does not add a newline. Needs $ or ~.
mark creates a point that can be jumped to or called as a subroutine.
jump equivalent of goto in batch (or any language for that matter).
proc calls a subroutine. Equivalent of call :label.
return returns from a subroutine. Will exit the program when not inside one.
if conditional instruction. Takes comparison from the next line, in the form <var1> <operator> <var2>. Operators are the same as if's in batch, ie. EQU, NEQ, LSS, LEQ, GTR, GEQ. Will execute instructions after it only if the comparison is true.
endif ends an if statement.
cat concatenates two variables. cat a b will store the value of ab in a.

When none of these commands are found, the expression is treated as a variable assignment, using the first token as the variable name. $ and ~ behave the same as in print, but there is also a @ identifier. This treats the last token as a mathematical expression, passed to set /a. It includes most operators. If none of the three identifiers are found, this is a syntax error and the interpreter exits.

Interpreter (Windows Batch)

The interpreter actually translates the code into windows batch, places it in a temporary file and executes it. While it recognizes syntax errors in the Half language, the resulting batch script may cause issues, especially with special characters like parentheses, vertical bars etc.

@echo off

REM Half Interpreter / Translator

if exist ~~.bat del ~~.bat
if not exist "%1" call :error "File not found: '%1'"
set error=
setlocal enabledelayedexpansion
call :parse "%1" 1>~~.bat
if exist ~~.bat if not "error"=="" ~~.bat 2>nul
goto :eof

:parse
set ifstate=0
echo @echo off
echo setlocal
echo setlocal enabledelayedexpansion
for /f "eol=# tokens=1,2* delims= " %%a in (%~1) do  (
    if "!ifstate!"=="1" (
        if /i not "%%b"=="equ" if /i not "%%b"=="neq" if /i not "%%b"=="lss" if /i not "%%b"=="leq" if /i not "%%b"=="gtr" if /i not "%%b"=="geq" call :error "Unknown comparator: '%%b'"
        echo if "^!%%a^!" %%b "^!%%c^!" ^(
        set ifstate=0
    ) else (
        if "%%a"=="print" (
            if "%%b"=="$" (
                echo echo.^^!%%c^^!
            ) else if "%%b"=="~" (
                echo echo.%%~c
            ) else call :error "Unknown identifier for print: '%%b'"
        ) else if "%%a"=="write" (
            if "%%b"=="$" (
                echo echo^|set/p="^!%%c^!"
            ) else if "%%b"=="~" (
                echo echo^|set/p="%%~c"
            ) else call :error "Unknown identifier for write: '%%b'"
        ) else if "%%a"=="mark" (
            if not "%%c"=="" call :error "Unexpected token: %%c"
            echo :%%b
        ) else if "%%a"=="jump" (
            if not "%%c"=="" call :error "Unexpected token: %%c"
            echo goto :%%b
        ) else if "%%a"=="proc" (
            if not "%%c"=="" call :error "Unexpected token: %%c"
            echo call :%%b
        ) else if "%%a"=="return" (
            if not "%%c"=="" call :error "Unexpected tokens: %%b %%c"
            if not "%%b"=="" call :error "Unexpected token: %%b"
            echo goto :eof
        ) else if "%%a"=="if" (
            if not "%%c"=="" call :error "Unexpected tokens: %%b %%c"
            if not "%%b"=="" call :error "Unexpected token: %%b"
            set ifstate=1
        ) else if "%%a"=="endif" (
            if not "%%c"=="" call :error "Unexpected tokens: %%b %%c"
            if not "%%b"=="" call :error "Unexpected token: %%b"
            echo ^)
        ) else if "%%a"=="cat" (
            echo set "%%b=^!%%b^!^!%%c^!"
        ) else (
            if "%%b"=="$" (
                echo set "%%a=!%%c!"
            ) else if "%%b"=="~" (
                echo set "%%a=%%~c"
            ) else if "%%b"=="@" (
                echo set/a"%%a=%%c"
            ) else call :error "Unknown tokens '%%a %%b %%c'"
        )
    )
)
echo endlocal
goto :eof

:error
echo.Parse Error: %~1 1>&2
set error=1
goto :eof