A cursory look at meta-programming in Nim (opens in new tab)

(blog.ldlework.com)

97 pointsldlework10y ago29 comments

29 comments

Or, with a text based meta-layer (MyDef):

    import macros

    $(for:A in A,B,C)
        proc $(A)() = echo "$(A)"

    proc execute(order: seq[int], callbacks: seq[proc]) =  
      for i in items(order):                              
        callbacks[i]()

    execute(@[0,0,1,2,1,2], @[A, B, C])

kazinator10y ago

You might as well use the POSIX shell to write your code:

   cat <<END
   $(for x in A B C; do
       echo "proc $x() = echo \"$x\"";
     done)
   
   proc execute(order: seq[int], callbacks: seq[proc]) =  
     for i in items(order):                              
       callbacks[i]()

   execute(@[0,0,1,2,1,2], @[A, B, C])
   END

rockboe10y ago

It's great that both Nim and Bash are so easy to read and write. The beauty of Nim is it makes writing performant C code as easy as writing Python.

hzhou32110y ago

It worked!

Now how do I incorporate this into my tool chain (Makefile)?

1 more reply

HOLYCOWBATMAN10y ago

Hey i can do that in $php too!

    function execute($order, $callbacks){
        foreach($order as $i){
            $callbacks[$i]();
        }
    }

    function abcProcs(){
        foreach(func_get_args() as $f){
            eval("function $f() { echo '$f'; };");
        }
    }

    abcProcs("A","B","C");
    execute([0,0,1,2,1,2], ['A','B','C']);

edit:

you don't have to quote the function names (just to show they are really functions and not closures):

    execute([0,0,1,2,1,2], [A,B,C]);

rockboe10y ago

Most scripting languages have miserable performance characteristics and lack native types. The beauty of Nim is it isn't a scripting language, it just looks like it is.

Nim isn't C/C++, but it performs like it is C/C++. Nim isn't Golang, either, but it compiles programs like Go does, down to a self-contained binary with no dependencies. You can even statically link a Nim program against musl libc to ship without even a dependency on glibc.

This puts a completely new spin on writing performant code - just skip the C and write your code in pure Nim. It's a lot like writing Python except you produce comparable results to what you would get from writing your code in C or Go.

kazinator10y ago

Way too cumbersome, sorry.

TXR Lisp:

  @(do
    (macro-time
      (defun abc-proc (n)
        ^(defun ,n () (pprinl ',n))))

    (defmacro abc-procs (. n)
      ^(progn ,*[mapcar abc-proc n]))

    (abc-procs a b c)

    (defun exec (order callbacks)
      (each ((i order))
        [[callbacks i]]))

    (exec '(0 0 1 2 1 2) '(a b c)))

  $ txr test.txr
  a
  a
  b
  c
  b
  c

Variation on exec:

  (defun exec (order callbacks)
    (mapdo (op [callbacks @1]) order))

def-10y ago

You can do it a bit shorter and easier in Nim as well:

    import macros, strutils
    
    macro abcProcs(n: varargs[expr]): stmt =
      result = newStmtList()
      for c in n.children:
        result.add parseStmt("proc $1 = echo \"$1\"" % $c)
    
    abcProcs("A","B","C")
    
    proc execute(order: openarray[int], callbacks: openarray[proc]) =
      for i in order:
        callbacks[i]()
    
    execute([0,0,1,2,1,2], [A,B,C])

andybak10y ago

Yes but on the plus side there's a lot fewer parentheses.

kazinator10y ago

If you're counting tokens, you should count all of them: all symbols and punctuation, as well as any whitespace outside of a string literal that cannot be replaced by a single space character without affecting the syntax.

1 more reply

ldleworkOP10y ago

You were down-voted but I secretly agree.

wait - oops. :)

shasta10y ago

I think the author should post a follow-up after he's tried to do substantial work with this style meta-programming. My guess is that you want to keep templated code to an absolute minimum.

ldleworkOP10y ago

You were down-voted but I actually agree. I did conclude the article by saying that templates seem really nice for closing the gap on refactoring code that not even generics could wrap up. So the intention was to convey that templates are really a last resort secret weapon. They just also seem to be pretty easy to understand :)

kbd10y ago

It's a small thing, but I'm so glad they renamed it to "Nim". Its prior name carries such a negative connotation, while just shortening that gave a name that's cute and simple.

jwecker10y ago

Fun fact- Nimrod means mighty hunter. The negative connotation came from early Bugs Bunny cartoons where he applies the name sarcastically to Elmer Fudd.

evilduck10y ago

Kind of. https://en.wikipedia.org/wiki/Nimrod

There's definitely a much older negative connotation than the Bugs Bunny usage.

1 more reply

sigzero10y ago

Also a very cool future sentinel in the X-Men comics.

Dewie310y ago

The voices of American programmers are loud and many.

1 more reply

vezzy-fnord10y ago

I'm one who actually preferred Nimrod, but it's done by now.

david-given10y ago

Ah --- I didn't know this was Nimrod! I remember looking at that a few years ago and thinking 'this is awesome but not quite ready yet'.

I need to have another look at Nim. It even looks like it's in Debian!

Dewie310y ago

`git` also carries negative connotations. But at least that was intentional.

j / k navigate · click thread line to collapse

29 comments

hzhou32110y ago

Or, with a text based meta-layer (MyDef):

    import macros

    $(for:A in A,B,C)
        proc $(A)() = echo "$(A)"

    proc execute(order: seq[int], callbacks: seq[proc]) =  
      for i in items(order):                              
        callbacks[i]()

    execute(@[0,0,1,2,1,2], @[A, B, C])

kazinator10y ago

You might as well use the POSIX shell to write your code:

   cat <<END
   $(for x in A B C; do
       echo "proc $x() = echo \"$x\"";
     done)
   
   proc execute(order: seq[int], callbacks: seq[proc]) =  
     for i in items(order):                              
       callbacks[i]()

   execute(@[0,0,1,2,1,2], @[A, B, C])
   END

rockboe10y ago

It's great that both Nim and Bash are so easy to read and write. The beauty of Nim is it makes writing performant C code as easy as writing Python.

hzhou32110y ago

It worked!

Now how do I incorporate this into my tool chain (Makefile)?

1 more reply

HOLYCOWBATMAN10y ago

Hey i can do that in $php too!

    function execute($order, $callbacks){
        foreach($order as $i){
            $callbacks[$i]();
        }
    }

    function abcProcs(){
        foreach(func_get_args() as $f){
            eval("function $f() { echo '$f'; };");
        }
    }

    abcProcs("A","B","C");
    execute([0,0,1,2,1,2], ['A','B','C']);

edit:

you don't have to quote the function names (just to show they are really functions and not closures):

    execute([0,0,1,2,1,2], [A,B,C]);

rockboe10y ago

Most scripting languages have miserable performance characteristics and lack native types. The beauty of Nim is it isn't a scripting language, it just looks like it is.

kazinator10y ago

Way too cumbersome, sorry.

TXR Lisp:

  @(do
    (macro-time
      (defun abc-proc (n)
        ^(defun ,n () (pprinl ',n))))

    (defmacro abc-procs (. n)
      ^(progn ,*[mapcar abc-proc n]))

    (abc-procs a b c)

    (defun exec (order callbacks)
      (each ((i order))
        [[callbacks i]]))

    (exec '(0 0 1 2 1 2) '(a b c)))

  $ txr test.txr
  a
  a
  b
  c
  b
  c

Variation on exec:

  (defun exec (order callbacks)
    (mapdo (op [callbacks @1]) order))

def-10y ago

You can do it a bit shorter and easier in Nim as well:

    import macros, strutils
    
    macro abcProcs(n: varargs[expr]): stmt =
      result = newStmtList()
      for c in n.children:
        result.add parseStmt("proc $1 = echo \"$1\"" % $c)
    
    abcProcs("A","B","C")
    
    proc execute(order: openarray[int], callbacks: openarray[proc]) =
      for i in order:
        callbacks[i]()
    
    execute([0,0,1,2,1,2], [A,B,C])

andybak10y ago

Yes but on the plus side there's a lot fewer parentheses.

kazinator10y ago

1 more reply

ldleworkOP10y ago

You were down-voted but I secretly agree.

wait - oops. :)

shasta10y ago

I think the author should post a follow-up after he's tried to do substantial work with this style meta-programming. My guess is that you want to keep templated code to an absolute minimum.

ldleworkOP10y ago

kbd10y ago

It's a small thing, but I'm so glad they renamed it to "Nim". Its prior name carries such a negative connotation, while just shortening that gave a name that's cute and simple.

jwecker10y ago

Fun fact- Nimrod means mighty hunter. The negative connotation came from early Bugs Bunny cartoons where he applies the name sarcastically to Elmer Fudd.

evilduck10y ago

Kind of. https://en.wikipedia.org/wiki/Nimrod

There's definitely a much older negative connotation than the Bugs Bunny usage.

1 more reply

sigzero10y ago

Also a very cool future sentinel in the X-Men comics.

Dewie310y ago

The voices of American programmers are loud and many.

1 more reply

vezzy-fnord10y ago

I'm one who actually preferred Nimrod, but it's done by now.

david-given10y ago

Ah --- I didn't know this was Nimrod! I remember looking at that a few years ago and thinking 'this is awesome but not quite ready yet'.

I need to have another look at Nim. It even looks like it's in Debian!

Dewie310y ago

`git` also carries negative connotations. But at least that was intentional.

j / k navigate · click thread line to collapse