Nicolas Williams
9deee38dc8
Now we have the ability to define a generator in jq:
def for(cond; update):
def _for:
if cond then ., (update | _for) else . end;
_for;
for(. < 10; . + 1) # generates numbers between `.` and 10
Running this by hand with --debug-dump-disasm (with a fix for that
coming up next) we can see that the call to _for is optimized:
_for:0:
0000 DUP
0001 CALL_JQ cond:0^1
0005 JUMP_F 0022
0007 POP
0008 FORK 0012
0010 JUMP 0020
0012 CALL_JQ update:1^1
0016 TAIL_CALL_JQ _for:0^1
0020 JUMP 0023
0022 POP
0023 RET
And timing this with 1000, 10000, 100000 iterations shows that
indeed we must be applying TCO; otherwise, without TCO, this gets
very slow very quickly.
jq
jq is a command-line JSON processor.
If you want to learn to use jq, read the documentation at http://stedolan.github.io/jq. This documentation is generated from the docs/ folder of this repository. You can also try it online at jqplay.org.
If you want to hack on jq, feel free, but be warned that its internals are not well-documented at the moment. Bring a hard hat and a shovel. Also, read the wiki: http://github.com/stedolan/jq/wiki
If you're building directly from the latest git, you'll need flex and bison installed. To build, run:
autoreconf -i
./configure
make -j8
make check
After make finishes, you'll be able to use ./jq. You can also
install it using:
sudo make install
If you're not using the latest git version but instead building a
released tarball (available on the website), then you won't need to
run autoreconf (and shouldn't), and you won't need flex or bison.
To cross-compile for OS X and Windows, see docs/Rakefile's build task and scripts/crosscompile. You'll need a cross-compilation environment, such as Mingw for cross-compiling for Windows.