Yesod-platform installation failing because of Alex package

Question

I'm trying to update the yesod platform to the latest version. In order to do this, I have executed the following commands:

cabal update
cabal install yesod-platform yesod-bin

To which I eventually get the following error:

Resolving dependencies...
Configuring language-javascript-0.5.13...
cabal: The program alex version >=3.0.5 is required but the version found at /usr/bin/alex is version 3.0.1
cabal: Error: some packages failed to install:
hjsmin-0.1.4.6 depends on language-javascript-0.5.13 which failed to install
language-javascript-0.5.13 failed during the configure step. The exception was:
ExitFailure 1
yesod-platform-1.2.12.2 depends on language-javascript-0.5.13 which failed to install
yesod-static-1.2.4 depends on language-javascript-0.5.13 which failed to install

After a bit of research, I have stumbled on the following post which mentions I should install a few more dependencies manually before doing the cabal install yesod-platform yesod-bin command. Those dependencies include alex amongst others. This, unfortunately, did not help as I got the same errors when I tried again.

I have then noticed that the version of alex in my /usr/bin/alex is still 3.0.1 after the manual install of alex version 3.0.5. After a bit of research, it seems when installing that package, it installs it in the $HOME/.cabal/bin and that path was not in my $PATH variable, so I added it in the /etc/environment file before the the entry /usr/bin/. After a reboot of my server, I have once again tried, but still get the same error.

Even if I added $HOME/.cabal/bin before /usr/bin/, it still goes in the latter to look for alex, which seems to be the problem. Other than copying the executable of alex version 3.0.5 from $HOME/.cabal/bin to /usr/bin/ manually (which I'm scared would cause me some problems, and headaches when wanting to update in the future), what could I do? Is this the real problem here?

Also, as a side question, when I echo $PATH, the $HOME is not resolved to /home/<myusername> (I see $HOME/...), is this normal?

EDIT: Tried renaming alex to alex.bak in /usr/bin/ to try and "force" ubuntu to take the one from $HOME/.cabal/bin, but it now cannot find any program named alex. Why is it not finding it in $HOME/.cabal/bin?

Answer 1

As it turned out the problem was just the usual path problems. Cabal installs new executables like alex into

/home/[you]/.cabal/bin (or ~/.cabal/bin) on linux

So you should set up your path to look there first.

You can to this temporary by writing

export PATH=/home/[you]/.cabal/bin:$PATH in your terminal before doing any Haskell stuff but normaly you might want to add this to a login-script.

The best place for this is IMO /home/[you]/.profile (or ~/.profile) so edit this file (or create it if it does not exist) and add these lines to the end of the file:

if [ -d "$HOME/.cabal/bin" ] ; then
    PATH="$HOME/.cabal/bin:$PATH"
fi

As this one takes care of the $HOME var to it should work just fine. Of course this one will only work after you loged in again.

You can test it with

whereis alex and alex --ver - the first one should point you to this path too, the second one should print out your current version of alex.

Have fun.

PS: replace [you] with your name within Linux everywhere of course ;)