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  • Have the gcc compiler on your machine
    git clone
    cd dclang
    ./dclang -i examples/some_primes.dc
  • You can also put the executable in /usr/local/bin or what-have-you.

  • Experiment as you wish with compiler optimizations in the Makefile, particularly with float-point options, since 'dclang' is heavily reliant on them.

  • For interaction, it's nice to use 'rlwrap' to get readline line-history:

    rlwrap ./dclang


dclang is an RPN, stack-based language with near-zero syntax. It is in the spirit and tradition of forth and the grand ol' RPN calculator dc, which is oft-found on a UNIX/LINUX system near you! You can think of it as a dialect of forth, much in the same way scheme is a leaner dialect of lisp. Why dclang and not gforth? For the same reasons one would choose scheme instead of lisp! Smaller, easier to learn, in some ways, better in terms of usability and syntactical and naming improvements. I wanted to take what I like about forth, shave off what I didn't like, and make a more user-friendly idealized version of forth -- one that forth folks would recognize, but also would perhaps be friendlier to new users.

There are two constant goals of dclang:

  1. to present hackers with a USABLE tool that they will enjoy!
  2. to create a lean, performant tool that utterly smokes most interpreted languages.

I do not want to get stuck in exploring CS theory (although that is respectable and interesting) so much that I have a "Turing Tarpit Tool" that does nothing. dclang is slowly gathering features that means you can use it like you'd use python, bash, gforth, etc...and I have an eye to be guided by some of the key "daily use" functionality that is for instance offered by glibc in C. In fact, you might say that I'll know dclang is really done when every (or almost every) aspect/feature of glibc is somehow reflected in the in-built capabilities of dclang.

RPN means "Reverse Polish Notation". That means everything uses a 'point-free-form', and there are no parenthesis, since there is a completely level order of operation. Words operate on stack operands immediately, and leave the result on the stack immediately. This makes the interpreter/parser not only simple but faster than one that has to do computational gymnastics around parsing things like braces or parenthesis, etc. It also saves memory, since you don't have runaway linked-list creation that you have to later garbage-collect. All actions happen on the stack. Like forth, this is not and never will be a garbage collected language, but there will be operations to create variables and other data structures like lists and hashes (dictionaries) and so on, but they will be manually destroyed in memory to make room for other structures with other keywords ('free'). No garbage collection means things are kept simple, and the programmer is assumed to be a thoughtful and responsible adult. :) forth is a great language, and I mean to follow that lead, even as I simplify certain aspects of the forth standard in this dialect.

The trade-off for that simplicity is that one has to get used to how order of operations work in this world (everything being immediate and w/o parenthesis). And also, one has to get used to manipulating the stack such that defined words make sensible, efficient use of the stack. It takes some getting used to. I direct the user to the internet or books to search for things relating to the fine art of programming forth, etc. Everything said there applies here.

Anyway, due to RPN, things will look like this, when you do math:

    4 5 + .

    20 5 / .

    0.523 sin .

    3 2.54 pow .

    1 2 3 5 + 7 16 / .s
    <4> 1 2 8 0.4375

    # a function!
    : testif 1 if "true" else "false" endif print cr ;

    # times/again -- basic, fastest loop type, starts at zero, ascends to cutoff parameter (minus one).
    : looptest 7 times i . again ;
    0 1 2 3 4 5 6

    # for/next loop, a little slower than basic 'times/again', but gives step options.
    # Parameters are to/from/step.
    # Let's add the first 20 million integers!
    : for_test 0
        20000001 1 1 for
            i +
        next . cr ;

    # this is a comment
    "This is a string!" print
    This is a string!

    # create a variable and store a value at it:
    var mynum
    4.321 3 / mynum !
    mynum @ .

    # low-level approach to do the same -- store a value at slot 11:
    1.15123 11 !
    0 @ .

Notice the '.' character, which pops/prints the top-of-stack (TOS). This comes from forth, as does '.s', which non-destructively shows the stack contents. This is different from 'dc', where 'p' pops/prints the TOS.

In the looping examples, the block has access to up to 3 hidden variables, 'i', 'j', and 'k' which you can use to test conditionally and escape the loop. This allows nested loops up to three counters deep. Going any futher is a code-smell anyway, and you should refactor to a different implementation if you need something more.

Implemented thus far:

  • Math:

    • +, -, *, /, %, <<, >>
    • abs, min, max, round, ceil, floor (float-versions only)
    • pow, sqrt, log, log2, log10 (float-versions only)
    • sin, cos, tan, pi, e (float-versions only)
    • rand (float-versions only)
  • Logic:

    • and, or, not, xor
    • =, <>, >, <, >=, <=
  • Stack operations:

    • drop, dup, over, swap, pick, 2drop, 2dup, 2over
    • svpush, svpop, svdrop, svpick
    • depth, clear, svdepth, svclear
  • Control structures:

    • if-else-endif
    • times/again; for/next (looping)
    • user-defined words (functions)
  • Strings:

    • simple string printing w/ print
    • fancier right-justified numeric output fields: .rj
    • strtok, mempcpy, memset, mkbuf, free
    • strong comparison with: strlen, str=, str<, str>
    • find a substring with strfind
    • '#' to end-of-line' for comments
    • uemit, a unicode-character emitter which can help to contruct strings that need them.
    • convert character bytes to equivalent numerical value with ord
    • convert integers to hex-string with tohex.
  • Variables/Arrays:

    • Declare a constant with const:

      1 pi 2 * / const INV2PI
    • Declare a variable with var:

      var myvar


      # This declares _and_ initializes:
      var myvar 42 myvar !


      # Declare a variable and advance the variable pointer such
      # that the variable owns 16 slots, making it an array. You
      # are responsible for knowing the bounds of the array yourself.
      # there are no protections keeping you from writing into neighboring
      # cells:
      var myarr 16 allot

      There is also create, which does something similar, but is paired typically with , which is an operator to place a stack value immediately into a storage location. So, to initialize an array of four values to 1, you'd do:

      create myarr 1 , 1 , 1 , 1 ,

      Note that the comma operator is an actual operator-word, it's not a delimiter!

    • ! (poke a value to a given slot, e.g. 5 funvar ! puts the value 5 into funvar)

    • @ (peek a value, copy it to the stack, e.g. funvar @ will put our previously saved '5' onto the top of the stack.

    • Since the variables exist in an giant global array, there really is no distinction between 'arrays' and 'variables' in dclang. Named variables or constants can be emulated by makings them words, e.g.:

      # make 'myvar' an alias for array slot number 53
      # N.B. this does *not* make myvar = 53; instead it give a name
      # to the slot that will hold the actual value.
      : myvar 53 ;
      # this will store 7.4231 into slot 53
      7.4231 myvar !
      myvar @ .
    • This works in a similar fashion for something like a string variable (which is, in reality an address and a length):

      : greeting "Hello there, good people!" ;
      greeting .s
      <1> 94123539921536
      greeting print cr
       Hello there, good people!
  • A global hash table (string keys and string values only). This is in the spirit of redis, in a way:

    "some value" "mykey" h!
    "mykey" h@ print cr
    some value
  • Timing:

    • a clock function ('clock') so we can time execution in nanoseconds for benchmarking.
    • A hook into CPU-cycle clock, called 'rdtsc'. (not available on RPi)
    • A sleep function (C's nanosleep under-the-hood)
  • Importing a file of dclang code:

    • From the interpreter
      "examples/some_primes.dc" import
    • On the command-line, then drop to interpreter:
      ./dclang -i examples/some_primes.dc
  • Read/write of file:

    var myfile
    "test_file.txt" "w+" fopen myfile !  # save the open file ptr to a var slot
    "Some text in my file! Woo-hoo!\n"
    myfile @ fwrite                       # write a sentence
    myfile @ fclose                       # close the file
    "test-file.txt" "r" fopen myfile !    # re-open for reading
    var buf 1024 mkbuf buf !              # create a memory buffer
    buf @ myfile @ 30 fread               # read 30 bytes from file, put in 'buf'
    # will print: Some text in my file! Woo-hoo!
    buf @ print cr
    myfile @ fclose                       # close the file
  • tcplisten, tcpaccept for server primitives, tcpconnect for clients. See the examples directory.


  • More time functions (e.g. date, calendar stuff, etc.)
  • More string functions, as needed. We have most of the basic string.h C-level functions. What could be implemented would be things like search/replace and regex.
  • The dsp.dc lib has a good start! But it is growing still...this is an active area for my interests!
  • More OS-level integration (directories, permissions, etc.)
  • Turtle graphics for the kids!?


Aaron Krister Johnson

Please report bugs and successes to


dclang, an RPN language descending from dc and Forth.





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