# glob-imports
A Haskell source preprocessor which generalizes `persistent-discover` and
`hspec-discover`, allowing you to metaprogram with source files.
A big limitation of `TemplateHaskell` is that it cannot modify the import list
of a file. The only way to metaprogram with the imports is to use a source
preprocessor like this.
## As an executable
Let's say you've got a ton of `persistent` database models, all defined in a
module hierarchy like this:
```
src/
Models/
Foo.hs
Bar.hs
Baz.hs
Blargh.hs
What.hs
OhNo.hs
```
If you're using `persistent` to automatically generate migrations, you'll want
to have all the `[EntityDef]` in scope from each module. You can do that by
importing each module that defines models and calling `$(discoverEntities)`,
introduced in `persistent-2.13`.
But you may forget to import a module.
This utility splices in a qualified import statement for *all* the modules defined in the
current directory and sub-directories, along with a list of imported modules. From this, you can use
[`discover-instances`](https://hackage.haskell.org/package/discover-instances)
or other `TemplateHaskell` code to work with these.
To use it, place the following command in a file, located in the same directory
that your Haskell modules are in:
```haskell
-- src/Models/All.hs
{-# OPTIONS_GHC -F -pgmF glob-imports #-}
module Models.All where
import Database.Persist.Sql
-- GLOB_IMPORTS_SPLICE
allEntities :: [EntityDef]
allEntities = $(discoverEntities)
```
The preprocessor will glob files in the current directory, and import all of
them qualified. The result would look like this:
```haskell
-- src/Models/All.hs
-- post-processed
module Models.All where
import Database.Persist.Sql
import qualified Models.Foo
import qualified Models.Bar
import qualified Models.Baz
import qualified Models.Blargh
import qualified Models.What
import qualified Models.OhNo
_importedModules :: [String]
_importedModules =
[ "Models.Foo"
, "Models.Bar"
, "Models.Baz"
, "Models.Blargh"
, "Models.What"
, "Models.OhNo"
]
allEntities :: [EntityDef]
allEntities = $(discoverEntities)
```
You'll need to add `glob-imports` to the `build-tool-depends` on your cabal file
for this to work.