TIL: never depend on the order of evaluation of sub-expressions in a stream

The code below may result in a 6 different execution orders. It will surprise and hurt you, so don't do that ;-)

std::cout << wizard.CastSpell("abracadabra") << wizard.DrinkPotion("Rosanke") << wizard.Mana();

More info can be found:

• http://stackoverflow.com/questions/14809978/order-of-execution-in-operator
• EXP10-C. Do not depend on the order of evaluation of subexpressions or the order in which side effects take place

Endless extracting of tar.bz2 archive

Funny story. Over a year ago I've backed up a project directory to tar.bz2 archive. Today I've decided to check what's inside. I've encountered a frozen window of 'extract here' option from file context menu.

I've killed the extract process and rerun it from a terminal:

tar -xvvf archive.tar.bz2

After few normal lines i've seen smth (in fact thousands of such lines):

hrwxr-x--- user/group       0 2013-02-06 23:20 workspace/a/b/a/b/f.go link to workspace/a/b/f.go
hrwxr-x--- user/group       0 2013-02-06 23:20 workspace/a/b/a/b/a/b/f.go link to workspace/a/b/a/b/f.go

This clued me, that probably the archive kept the symbolic links. After Googling and reading tar manual I had this idea: let's remove a symlink from an archive:

tar --delete -f archive.tar workspace/a/b/a

This worked just well :-)

pep8

I've got very comfortable with clang-format for C++ and gofmt for Go. Every time I have to use some other language i'm missing them very much. Today I've found a solution for Python. It makes life so much easier. The two awesome tools are:

pep8

pep8 is a tool to check your Python code against some of the style conventions in PEP 8.

https://pypi.python.org/pypi/pep8

autopep8

autopep8 automatically formats Python code to conform to the PEP 8 style guide. It uses the pep8 utility to determine what parts of the code needs to be formatted. autopep8 is capable of fixing most of the formatting issues that can be reported by pep8.

https://github.com/hhatto/autopep8

Torch7 weird error and Google Search without a solution

The below is an error one gets when working with Torch7 from time to time:

/usr/local/bin/luajit: /usr/local/share/lua/5.1/nn/Tanh.lua:4: attempt to index field 'nn' (a nil value)
stack traceback:
 /usr/local/share/lua/5.1/nn/Tanh.lua:4: in function 'updateOutput'
 /usr/local/share/lua/5.1/nn/Sequential.lua:29: in function 'updateOutput'
 /usr/local/share/lua/5.1/nn/Sequential.lua:29: in function 'forward'
 main.lua:93: in function 'opfunc'
 /usr/local/share/lua/5.1/optim/sgd.lua:43: in function 'sgd'
 main.lua:117: in function 'train3'
 main.lua:142: in main chunk
 [C]: in function 'dofile'
 /usr/local/lib/luarocks/rocks/trepl/scm-1/bin/th:131: in main chunk
 [C]: at 0x00406260

Reading a bit about similar errors(1) I've concluded that probably the type of Tensor is wrong. I work on torch.CudaTensor objects, why the problem? I've forgot to import the correct library:

require("cunn")

Reflex - trigger an execution of command on a file change event

How many times you were working on some tiny project that needs to be rebuild / restarted after you modify the code? I guess often.

After experimenting with some solutions I found an ultimate one: https://github.com/cespare/reflex
Installation:

go get github.com/cespare/reflex

Automatically recompiling markdown file into html every time the file is changed:

reflex -r '\.md$' blackfriday-tool -page article.md article.html

Or you can restart Go app when saved files:

reflex -r '\.go$' -- go run main.go