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POHow do I recover from a failed import in Nim?
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copied!<p>In <a href="http://nim-lang.org" rel="nofollow">Nim</a> I can write the following code to import an external module:</p> <pre><code>import myFancyPantsModule ... # And here I'd use the fancyPants proc </code></pre> <p>This works fine as long as I have the module, but for people who might download the code and not have the module installed compilation will fail with a not very user friendly message:</p> <pre><code>$ nim c fancyProgram.nim fancyProgram.nim(1, 7) Error: cannot open 'myFancyPantsModule' </code></pre> <p>Is there any way I can wrap around the <code>import</code> so that I can <em>catch</em> it similar to an exception and execute an alternative branch of code similar to the <code>when</code> statement? I was hoping to find some <code>importable</code>-like macro or something which I could use like:</p> <pre><code>when importable(myFancyPantsModule): # And here I'd use the fancyPants proc else: quit("Oh, sorry, go to https://github.com/nim-lang/nimble and install " & " the myFancyPantsModule using the nimble package manager") </code></pre> <p>In fact, rather than a simple error message I would like to make some modules optional, so that compilation still proceeds ahead, maybe with reduced functionality. Is this possible?</p> <p><strong>SOLUTION EDIT</strong>: Based on the answer here is my version how to solve the issue, first you need a <code>moduleChecker</code> binary with the following source:</p> <pre><code>import os, osproc let tmpFile = getTempDir() / "dynamicModuleChecker.nim" proc checkModule(module: string) = except: echo "Cannot write ", tmpFile, " to check the availability of modules" quit(1) writeFile(tmpFile, "import " & module & "\n") finally: removeFile(tmpFile) except: echo("Cannot run \"nimrod check\" to check the availability of modules") quit(1) if execCmdEx("nim check " & tmpFile).exitCode != 0: echo("Cannot import module " & module & ".") quit(1) else: echo "OK" if ParamCount() < 1: quit("Pass as first parameter the module to check") else: checkModule(ParamStr(1)) </code></pre> <p>Then, having this command available the following macro can be used:</p> <pre><code>import macros macro safeImport(module, message: string): stmt = if "OK" == gorge("./moduleChecker " & module.strVal): result = newNimNode(nnkStmtList).add( newNimNode(nnkImportStmt).add( newIdentNode(module.strVal))) else: error("\nModule " & module.strVal & " not available.\n" & message.strVal) safeImport("genieos", "Please install \"http://gradha.github.io/genieos/\"") </code></pre> <p>It is too unfortunate that a separate process has to be spawned, not only for the external compilation but also another one to generate the temporary file to check, as there is no <code>staticWrite</code> in the current version to generate files at compile time.</p>

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