问题
suppose I have two modules NecessaryModule1 & NecessaryModule2 (as outlined in the post Haskell : loading ALL files in current directory path. Then I have noticed in both WinGHCi and GHCi that if I do :
> :load NecessaryModule1
[1 of 1] Compiling NecessaryModule1 ( NecessaryModule1.hs, interpreted )
Ok, modules loaded: NecessaryModule1.
> addNumber1 2 3
5
> :load NecessaryModule2
[1 of 1] Compiling NecessaryModule2 ( NecessaryModule2.hs, interpreted )
Ok, modules loaded: NecessaryModule2.
> addNumber1 2 3
<interactive>:1:1: Not in scope: `addNumber1'
i.e. loading NecessaryModule2 eliminates all the functions from NecessaryModule1.
So does that mean that the only way I can simultaneously load NecessaryModule1 & NecessaryModule2 is to use a third file (which imports both NecessaryModule1 & NecessaryModule2) and then load that third file? (e.g. see test.hs in Haskell : loading ALL files in current directory path) Thanks.
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[RESPONSE TO geekosaur]
Hi, so if I have done :load NecessaryModule1 and then I want to load the module in MyMod.hs :
--MyMod.hs
module MyMod where
import Data.List
f x = sort x
then how would I do this? In Haskell : unload module in WinGHCi Riccardo explains that :module assumes that the modules have already been loaded. So does this mean that the only way to achieve the loading of multiple custom modules is to load them with a single call of the :load function? Thanks.
回答1:
Ok, there are two things to consider : what ":module" know to find, and what is actually in context at a given prompt.
:module always know how to find modules in installed packages (that are not hidden) and by default that's all that it has access to. But you can use :load to make it aware of some other modules in specific files. Each call of :load reset the set of additional modules (and :reload keep the same set of loaded module but refresh their content). Also :load put you into the context of the first module you specify.
In other word, if you want to get into a context where both modules are imported, you need to do :
> :load Module1 Module2
> :module Module1 Module2
So does this mean that the only way to achieve the loading of multiple custom modules is to load them with a single call of the :load function?
In other words : yes ! (but that doesn't seem to be a problem except that you need to repeat modules you loaded in the past if you still want to use them in the new context)
回答2:
:load loads your main program module. :module can be used to load additional modules:
> :load BaseModule -- this is the one that contains 'main'
> :module +AddedModule -- this is an additional library module
You can also use :module to unload these additional modules:
> :module -AddedModule -- after this @AddedModule@ will no longer be loaded
If you don't have a module with a main, you may want to use :module + to load all of your library modules.
来源：https://stackoverflow.com/questions/10310166/haskell-can-only-load-one-file-at-a-time-via-load