Haskell: Difference between revisions

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=== Using shellFor (multiple packages) ===

~~<code>~~shellFor~~</code>~~ is similar to <code>developPackage</code> but (slightly) more complicated to also allow you to develop multiples packages at the same time (~~similar to <code>~~cabal.project~~</code>~~). Note that contrary to <code>developPackage</code> I don't think that <code>shellFor</code> can output a derivation.

[https://nixos.org/manual/nixpkgs/stable/#haskell-shellFor shellFor] is similar to <code>developPackage</code> but (slightly) more complicated to also allow you to develop multiples packages at the same time (it can work in conjuction with [https://cabal.readthedocs.io/en/stable/cabal-project-description-file.html cabal.project]). Note that contrary to <code>developPackage</code> I don't think that <code>shellFor</code> can output a derivation.

The idea is to first extend/override the set of haskell packages in order to add your projects as additional haskell packages (for instance using <code>haskellPackages.extend</code> and <code>packageSourceOverrides</code> that just need the path of the project to compile it), and then to use <code>haskellPackages.shellFor {packages= p: [p.myproject1 p.myproject2]}</code> to create a shell with all wanted packages.

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For instance you can define your various projects in subfolders <code>./frontend</code> and <code>./backend</code> (you can use cabal init to create the content in each folder), then create a file <code>cabal.project</code> containing:

<~~syntaxhighlight lang=text~~>

{{file|cabal.project|nix|

packages:

frontend/

backend/

</~~syntaxhighlight~~>

</nowiki>

}}

Finally ~~create~~ a ~~file~~ <code>shell.nix</code> containing:

Finally you define a nix shell in <code>shell.nix</code> containing:

<~~syntaxhighlight lang="nix"~~>

{{file|shell.nix|nix|

with import <nixpkgs> {};

with import </nowiki><<nowiki>nixpkgs</nowiki>><nowiki> {};

# We add our packages to the haskell package set

(haskellPackages.extend (haskell.lib.compose.packageSourceOverrides {

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buildInputs = [ pkgs.python pkgs.cabal-install ];

}

</~~syntaxhighlight~~>

</nowiki>

}}

then you can use cabal to develop incrementally your projects using for instance:

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$ nix-shell

$ cabal ~~new-~~build all

$ cabal build all

</syntaxhighlight>

If you want to be able to compile a project non-incrementally with <code>nix-build</code> (say the backend in the above example) you can put in <code>default.nix</code>:

<~~syntaxhighlight lang="nix"~~>

with import <nixpkgs> {};

{{file|default.nix|nix|

with import </nowiki><<nowiki>nixpkgs</nowiki>><nowiki> {};

# We add our packages to the haskell package set

(haskellPackages.extend (haskell.lib.compose.packageSourceOverrides {

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backend = ./backend;

})).backend

</~~syntaxhighlight~~>

</nowiki>

}}

or if you want to create a single derivation file, you can use <code>if pkgs.lib.inNixShell then … else …</code> to output the shell when we start a shell and the packages when we want to build them. You can find [https://github.com/kowainik/summoner/blob/60de4f2f087e5bd2beaad9253e7eded731cfbaaf/default.nix here] an example.

@@ Line 147: / Line 147: @@
 ===  Using shellFor (multiple packages) ===
-<code>shellFor</code> is similar to <code>developPackage</code> but (slightly) more complicated to also allow you to develop multiples packages at the same time (similar to <code>cabal.project</code>). Note that contrary to <code>developPackage</code> I don't think that <code>shellFor</code> can output a derivation.
+[https://nixos.org/manual/nixpkgs/stable/#haskell-shellFor shellFor] is similar to <code>developPackage</code> but (slightly) more complicated to also allow you to develop multiples packages at the same time (it can work in conjuction with [https://cabal.readthedocs.io/en/stable/cabal-project-description-file.html cabal.project]). Note that contrary to <code>developPackage</code> I don't think that <code>shellFor</code> can output a derivation.
 The idea is to first extend/override the set of haskell packages in order to add your projects as additional haskell packages (for instance using <code>haskellPackages.extend</code> and <code>packageSourceOverrides</code> that just need the path of the project to compile it), and then to use <code>haskellPackages.shellFor {packages= p: [p.myproject1 p.myproject2]}</code> to create a shell with all wanted packages.
@@ Line 153: / Line 153: @@
 For instance you can define your various projects in subfolders <code>./frontend</code> and <code>./backend</code> (you can use cabal init to create the content in each folder), then create a file <code>cabal.project</code> containing:
-<syntaxhighlight lang=text>
+{{file|cabal.project|nix|
+<nowiki>
 packages:
    frontend/
    backend/
-</syntaxhighlight>
+</nowiki>
+}}
-Finally create a file <code>shell.nix</code> containing:
+Finally you define a nix shell in <code>shell.nix</code> containing:
-<syntaxhighlight lang="nix">
+{{file|shell.nix|nix|
-with import <nixpkgs> {};
+<nowiki>
+with import </nowiki><<nowiki>nixpkgs</nowiki>><nowiki> {};
 # We add our packages to the haskell package set
 (haskellPackages.extend (haskell.lib.compose.packageSourceOverrides {
@@ Line 174: / Line 177: @@
      buildInputs = [ pkgs.python pkgs.cabal-install ];
    }
-</syntaxhighlight>
+</nowiki>
+}}
 then you can use cabal to develop incrementally your projects using for instance:
@@ Line 180: / Line 184: @@
 <syntaxhighlight lang="console">
 $ nix-shell
-$ cabal new-build all
+$ cabal build all
 </syntaxhighlight>
 If you want to be able to compile a project non-incrementally with <code>nix-build</code> (say the backend in the above example) you can put in <code>default.nix</code>:
-<syntaxhighlight lang="nix">
-with import <nixpkgs> {};
+{{file|default.nix|nix|
+<nowiki>
+with import </nowiki><<nowiki>nixpkgs</nowiki>><nowiki> {};
 # We add our packages to the haskell package set
 (haskellPackages.extend (haskell.lib.compose.packageSourceOverrides {
@@ Line 191: / Line 197: @@
    backend = ./backend;
 })).backend
-</syntaxhighlight>
+</nowiki>
+}}
 or if you want to create a single derivation file, you can use <code>if pkgs.lib.inNixShell then … else …</code> to output the shell when we start a shell and the packages when we want to build them. You can find [https://github.com/kowainik/summoner/blob/60de4f2f087e5bd2beaad9253e7eded731cfbaaf/default.nix here] an example.