xesite/blog/nim-and-tup-2015-06-10.markdown

title	date
Nim and Tup	2015-06-10

I have been recently playing with and using a new lanugage for my personal development, Nim. It looks like Python, runs like C and integrates well into other things. Its compiler targets C, and as a result of this binding things to C libraries is a lot more trivial in Nim; even moreso than with go.

For example, here is a program that links to the posix crypt(3) function:

# crypt.nim
import posix

{.passL: "-lcrypt".}

echo "What would you like to encrypt? "
var password: string = readLine stdin
echo "What is the salt? "
var salt: string = readLine stdin

echo "result: " & $crypt(password, salt)

And an example usage:

xena@fluttershy (linux) ~/code/nim/crypt
➜  ./crypt
What would you like to encrypt?
foo
What is the salt?
rs
result: rsHt73tkfd0Rg

And that's it. No having to worry about deferring to free the C string, no extra wrappers (like with Python or Lua), you just write the code and it just works.

At the idea of another coworker, I've also started to use tup for building things. Nim didn't initially work very well with tup (temporary cache needed, etc), but a very simple set of tup rules were able to fix that:

NIMFLAGS += --nimcache:".nimcache"
NIMFLAGS += --deadcodeElim:on
NIMFLAGS += -d:release
NIMFLAGS += -d:ssl
NIMFLAGS += -d:threads
NIMFLAGS += --verbosity:0

!nim = |> nim c $(NIMFLAGS) -o:%o %f && rm -rf .nimcache |>

This creates a tup !-macro called !nim that will Do The Right Thing implicitly. Usage of this is simple:

.gitignore
include_rules

: crypt.nim |> !nim |> ../bin/crypt

xena@fluttershy (linux) ~/code/nim/crypt
➜  tup
[ tup ] [0.000s] Scanning filesystem...
[ tup ] [0.130s] Reading in new environment variables...
[ tup ] [0.130s] No Tupfiles to parse.
[ tup ] [0.130s] No files to delete.
[ tup ] [0.130s] Executing Commands...
 1) [0.581s] nim c --nimcache:".nimcache" --deadcodeElim:on --verbosity:0 crypt.nim && rm -rf .nimcache
 [ ] 100%
[ tup ] [0.848s] Updated.

Not only will this build the program if needed, it will also generate a gitignore for all generated files. This is an amazing thing. tup has a lot more features (including lua support for scripting complicated build logic), but there is one powerful feature of tup that makes it very difficult for me to work into my deployment pipelines.

tup requires fuse to ensure that no extra things are being depended on for builds. Docker doesn't let you use fuse mounts in the build process.

I have a few ideas on how to work around this, and am thinking about tackling them when I get nim programs built inside Rocket images.