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POHow to use "cabal-dev ghci" with a non-sandbox, non-global (user?) package?
 

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  1. POHow to use "cabal-dev ghci" with a non-sandbox, non-global (user?) package?
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    <p>I'm trying out <code>cabal-dev</code> for a project I'm working on; the project is a library, and <code>cabal-dev</code> does a great job of building a sandboxed version of it - but I'm having trouble with part of my workflow...</p> <p>I have a script, <code>scratch.hs</code>, which (pre-<code>cabal-dev</code>) I would load into <code>ghci</code> for trying stuff out. The contents of <code>scratch.hs</code> change over time depending on what feature I'm working on, of course. <code>scratch.hs</code> isn't part of the library codebase, it's just my personal scratchspace while I'm working on it.</p> <p>Now, in order to get a <code>ghci</code> session with my sandbox loaded, I can just <code>cabal-dev ghci</code>, and then load <code>scratch.hs</code> into that. The problem is that this (by design, and sensibly) excludes my user package database, so if <code>scratch.hs</code> references modules from packages which aren't in my library's <code>build-depends</code> (which is not unreasonable - it's not part of the library after all), those packages aren't visible, and so I get an error such as:</p> <pre><code>scripts/scratch.hs:8:8: Could not find module `Data.Aeson.Generic': It is a member of the hidden package `aeson-0.3.2.11'. Perhaps you need to add `aeson' to the build-depends in your .cabal file. Use -v to see a list of the files searched for. Failed, modules loaded: none. </code></pre> <p>where, in this case, <code>scratch.hs</code> wants to import <code>Data.Aeson.Generic</code> but <code>aeson</code> is not in my library's <code>build-depends</code> (quite properly), but <em>is</em> in my user package database.</p> <p>So how can I work around this? I can imagine answers in either of these categories, but maybe there are categories I've missed:</p> <ol> <li><p>A way to (selectively) use packages from my user package database in conjunction with the sandbox created by <code>cabal-dev</code>. (Perhaps rolling my own <code>cabal-dev ghci</code> style script?)</p></li> <li><p>A suggestion on how to improve my workflow so the problem just goes away.</p></li> </ol> <p>I know I could just install the package globally, but I'm reluctant to pollute my global package database in this manner (and <code>cabal-dev</code> discourages this explicitly).</p> <p>Many thanks for all advice.</p>
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    1. USgimboland
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    1. COI wonder... can you :set -package from within ghci? (Or whatever the name of the option is that chooses your package database?)
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      1. POHow to use "cabal-dev ghci" with a non-sandbox, non-global (user?) package?
      1. USDaniel Wagner
    2. CO*slaps forehead* - why didn't I think of that? Yes, that works - thanks. I can even add it to `.ghci` and have it happen automatically. Thanks, Daniel!
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      1. POHow to use "cabal-dev ghci" with a non-sandbox, non-global (user?) package?
      1. USgimboland
    3. COOops, tell a lie. No, that doesn't work. It appeared to work earlier, but that was because my project's test-suite uses aeson, so it _was_ referenced in my .cabal file and thus brought in to the sandbox though not, it seems, implicitly loaded by `cabal-dev ghci`, which is why I needed `:set -package aeson` to load it. If I remove that, then in fact `:set -package aeson` _doesn't_ load the user package database version ("`cannot satisfy -package aeson`"), so I'm back where I started (except that everybody who's viewed this page in the last 3 hours thinks the problem is solved).
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      1. USgimboland
 

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