Shiryel shiryel

General notes

nix-channel and ~/.nix-defexpr are gone. We'll use $NIX_PATH (or user environment specific overrides configured via nix set-path) to look up packages. Since $NIX_PATH supports URLs nowadays, this removes the need for channels: you can just set $NIX_PATH to e.g. https://nixos.org/channels/nixos-15.09/nixexprs.tar.xz and stay up to date automatically.
By default, packages are selected by attribute name, rather than the name attribute. Thus nix install hello is basically equivalent to nix-env -iA hello. The attribute name is recorded in the user environment manifest and used in upgrades. Thus (at least by default) hello won't be upgraded to helloVariant.

@vcunat suggested making this an arbitrary Nix expression rather than an attrpath, e.g. firefox.override { enableFoo = true; }. However, such an expression would not have a key in the user environment, unlike an attrpath. Better to require an explicit flag for this.

TBD: How to deal with search path clashes.

The set lines

These lines deliberately cause your script to fail. Wait, what? Believe me, this is a good thing.
With these settings, certain common errors will cause the script to immediately fail, explicitly and loudly. Otherwise, you can get hidden bugs that are discovered only when they blow up in production.

set -e
set -u

	:def hoogle \x -> return $ ":!hoogle --count=15 \"" ++ x ++ "\""
	:def doc \x -> return $ ":!hoogle --info \"" ++ x ++ "\""
	:set -Wall
	:set -fno-warn-type-defaults -ferror-spans -freverse-errors -fprint-expanded-synonyms
	:set prompt "\ESC[0;32m%s\n\ESC[m[ghci]\ESC[38;5;172mλ \ESC[m"
	:set prompt-cont " \ESC[38;5;172m> \ESC[m"