Re: [Nix-dev] joining attribute sets recursively
On Mon, 16 Jan 2012 22:05:26 +0100, Nicolas Pierron
nicolas.b.pier...@gmail.com wrote:
(..)
mkX [ {
a = 1;
b = 1;
c.a = 1;
} {
b = 2;
c.b = 2;
d = 2;
} ]
possible results:
- error because of colliding b
- first value taken: { a = 1; b = 1; c = { a = 1; b = 2 }; d = 2}
- last value taken: { a = 1; b = 2; c = { a = 1; b = 2 }; d = 2}
- both values taken: { a = 1; b = [1 2]; c = { a = 1; b = 2 }; d = 2}
- both values taken: { a = 1; b = mkX [1 2]; c = mkX [ { a = 1; } { b
= 2; } ]; d = 2}
+1
Currently the cleanest way to do so is to duplicate the condition on
the attributes, such as:
config = {
boot = mkIf cfg.enable { … };
services = mkIf cfg.aggressive { … };
};
By the way, usually the enable condition is wrapping everything and
what you want to do makes me wonder if the aggressive option does not
deserve another name.
I would wrap everything with enable and additionally with aggressive you
can turn on more aggressive features.
Open for better suggestions.
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Re: [Nix-dev] joining attribute sets recursively
Now for one the syntax is incorrect
try this:
cfg.enable ({
...
} // (if cfg.aggressive then { .. } else { .. } ))
will be overriden with the value from the second attribute set.
there are merge functions defined in lib - but they are overkill.
The solution is to move and duplicate the mkIf or use two different
modules. I suggested to pierron adding a mkMerge function for exactly
that reason - and because mkElse can be used in uncommen ways.
I also rewrote the config system making this easy - but I have done no
testing yet.
Try this:
config.powerManagement = {
cpuFreqGovernor = ondemand;
scsiLinkPolicy = if (cfg.aggressive) then min_power else mkNoDef; // or
something similar, grep nixos code for its usages.
}
if mkNoDef doesn't work try the // trick shown above.
[.. infinite recursion ]
The problem is that cfg.aggressive can't be evaluated without evaluating
the top level config attrs. But that contains the condition!
Let me make it obvious:
config = mkIf cfg.enable ({
aggressive = true;
} // (if cfg.aggressive then {
} else { }));
in order to evaluate aggressive the module system has to evaluate the if
branch.. but in order to know whether it should be evaluated it has to
evaluate the condition .. in order to ... :-) You get the point.
HTH
Marc Weber
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Re: [Nix-dev] joining attribute sets recursively
On 16/01/12 15:37, Florian Friesdorf wrote:
config = mkIf cfg.enable {
...
powerManagement.cpuFreqGovernor = ondemand;
} // cfg.aggressive ? {
...
powerManagement.scsiLinkPolicy = min_power;
} : {};
Indeed it would be good to have a way of writing this down in a nice way.
(Using two different modules as Marc suggested isn't very elegant.) Maybe
something like
config = mkUnion
[ (mkIf cfg.foo {
... attrs ...
})
(mkIf cfg.bar {
... attrs ...
})
...
];
--
Eelco Dolstra | http://www.st.ewi.tudelft.nl/~dolstra/
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Re: [Nix-dev] joining attribute sets recursively
Excerpts from Eelco Dolstra's message of Mon Jan 16 16:50:10 +0100 2012:
config = mkUnion
That mkUnion is exactly what mkMerge should be doing.
Wait another week or two. I hope I have nixos running on my rewrite so that we
can benchmark both memory consumption and speed. If there are no
significant improvements in those two areas I'm likely to drop it again.
You can see the draft implementation here:
http://mawercer.de/~marc/config-eval-rewrite.patch
The test.nix contains examples about how mkMerge can be used.
Basically its still a {
options = ..
config = ..
}
declaration. I chose to make it explicit that required modules don't depend
on options. Not sure whether its making everything less readable.
Marc Weber
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Re: [Nix-dev] joining attribute sets recursively
On Mon, 16 Jan 2012 16:42:50 +0100, Marc Weber marco-owe...@gmx.de wrote:
Now for one the syntax is incorrect
try this:
cfg.enable ({
...
} // (if cfg.aggressive then { .. } else { .. } ))
I fail to see the difference to what I tried, which resulted in infinte
recursion, which you also explain below.
will be overriden with the value from the second attribute set.
there are merge functions defined in lib - but they are overkill.
The solution is to move and duplicate the mkIf or use two different
modules. I suggested to pierron adding a mkMerge function for exactly
that reason - and because mkElse can be used in uncommen ways.
I also rewrote the config system making this easy - but I have done no
testing yet.
Try this:
config.powerManagement = {
cpuFreqGovernor = ondemand;
scsiLinkPolicy = if (cfg.aggressive) then min_power else mkNoDef; // or
something similar, grep nixos code for its usages.
}
It's not just the scsiLinkPolicy but also a jobs definition and
eventually more.
if mkNoDef doesn't work try the // trick shown above.
[.. infinite recursion ]
The problem is that cfg.aggressive can't be evaluated without evaluating
the top level config attrs. But that contains the condition!
Let me make it obvious:
config = mkIf cfg.enable ({
aggressive = true;
} // (if cfg.aggressive then {
} else { }));
in order to evaluate aggressive the module system has to evaluate the if
branch.. but in order to know whether it should be evaluated it has to
evaluate the condition .. in order to ... :-) You get the point.
see above
--
Florian Friesdorf f...@chaoflow.net
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Re: [Nix-dev] joining attribute sets recursively
On Mon, 16 Jan 2012 16:50:10 +0100, Eelco Dolstra e.dols...@tudelft.nl wrote:
On 16/01/12 15:37, Florian Friesdorf wrote:
config = mkIf cfg.enable {
...
powerManagement.cpuFreqGovernor = ondemand;
} // cfg.aggressive ? {
...
powerManagement.scsiLinkPolicy = min_power;
} : {};
Indeed it would be good to have a way of writing this down in a nice way.
(Using two different modules as Marc suggested isn't very elegant.) Maybe
something like
config = mkUnion
[ (mkIf cfg.foo {
... attrs ...
})
(mkIf cfg.bar {
... attrs ...
})
...
];
hmm - not sure whether mkUnion or mkMerge (as Marc suggests) cuts
it. The term *merge* is pretty generic and it would depend on a merge
algorithm what happens. A union for sets is defined as all elements
without duplicates, with a quick search I could not find a definition
for key/val pairs / associative arrays / attribute sets. Maybe looking
at the possible behaviours helps finding a name:
mkX [ {
a = 1;
b = 1;
c.a = 1;
} {
b = 2;
c.b = 2;
d = 2;
} ]
possible results:
- error because of colliding b
- first value taken: { a = 1; b = 1; c = { a = 1; b = 2 }; d = 2}
- last value taken: { a = 1; b = 2; c = { a = 1; b = 2 }; d = 2}
- both values taken: { a = 1; b = [1 2]; c = { a = 1; b = 2 }; d = 2}
--
Florian Friesdorf f...@chaoflow.net
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Re: [Nix-dev] joining attribute sets recursively
On Mon, Jan 16, 2012 at 18:28, Florian Friesdorf f...@chaoflow.net wrote:
On Mon, 16 Jan 2012 16:50:10 +0100, Eelco Dolstra e.dols...@tudelft.nl
wrote:
On 16/01/12 15:37, Florian Friesdorf wrote:
config = mkIf cfg.enable {
...
powerManagement.cpuFreqGovernor = ondemand;
} // cfg.aggressive ? {
...
powerManagement.scsiLinkPolicy = min_power;
} : {};
Indeed it would be good to have a way of writing this down in a nice way.
(Using two different modules as Marc suggested isn't very elegant.) Maybe
something like
config = mkUnion
[ (mkIf cfg.foo {
... attrs ...
})
(mkIf cfg.bar {
... attrs ...
})
...
];
hmm - not sure whether mkUnion or mkMerge (as Marc suggests) cuts
it. The term *merge* is pretty generic and it would depend on a merge
algorithm what happens. A union for sets is defined as all elements
without duplicates, with a quick search I could not find a definition
for key/val pairs / associative arrays / attribute sets. Maybe looking
at the possible behaviours helps finding a name:
mkX [ {
a = 1;
b = 1;
c.a = 1;
} {
b = 2;
c.b = 2;
d = 2;
} ]
possible results:
- error because of colliding b
- first value taken: { a = 1; b = 1; c = { a = 1; b = 2 }; d = 2}
- last value taken: { a = 1; b = 2; c = { a = 1; b = 2 }; d = 2}
- both values taken: { a = 1; b = [1 2]; c = { a = 1; b = 2 }; d = 2}
- both values taken: { a = 1; b = mkX [1 2]; c = mkX [ { a = 1; } { b
= 2; } ]; d = 2}
Currently the cleanest way to do so is to duplicate the condition on
the attributes, such as:
config = {
boot = mkIf cfg.enable { … };
services = mkIf cfg.aggressive { … };
};
By the way, usually the enable condition is wrapping everything and
what you want to do makes me wonder if the aggressive option does not
deserve another name.
--
Nicolas Pierron
http://www.linkedin.com/in/nicolasbpierron - http://nbp.name/
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