### Haskell: Safe Resource Management with Bracketing Commands

Source: https://hackage.haskell.org/package/vulkan

Demonstrates the use of bracketing commands in Haskell for Vulkan resource management, ensuring that creation and destruction functions are paired correctly. These functions, prefixed with `with` or `use`, often leverage `Control.Exception.bracket` or similar mechanisms for safe allocation and deallocation. The example shows `withInstance` for managing Vulkan instances.

```haskell
createInstance
  :: forall a m
   . (PokeChain a, MonadIO m)
  => InstanceCreateInfo a
  -> Maybe AllocationCallbacks
  -> m Instance

destroyInstance
  :: forall m
   . MonadIO m
  => Instance
  -> Maybe AllocationCallbacks
  -> m ()

withInstance
  :: forall a m r
   . (PokeChain a, MonadIO m)
  => InstanceCreateInfo a
  -> Maybe AllocationCallbacks
  -> (m Instance -> (Instance -> m ()) -> r)
  -> r

```

```haskell
import Control.Monad.Trans.Resource (runResourceT, allocate)
-- Create an instance and print its value
main = runResourceT $ do
  (instanceReleaseKey, inst) <- withInstance zero Nothing allocate
  liftIO $ print inst

-- Begin a render pass, draw something and end the render pass
drawTriangle =
  cmdUseRenderPass buffer renderPassBeginInfo SUBPASS_CONTENTS_INLINE bracket_ 
    $ do
        cmdBindPipeline buffer PIPELINE_BIND_POINT_GRAPHICS graphicsPipeline
        cmdDraw buffer 3 1 0 0

```

--------------------------------

### Haskell: Handling Dual-Use Vulkan Commands

Source: https://hackage.haskell.org/package/vulkan

Illustrates how Haskell bindings handle Vulkan commands that have dual use: they can either return a count of available items or the items themselves. The bindings typically provide functions that automatically fetch all results, simplifying the common Vulkan idiom of querying the count first and then allocating memory to retrieve the data. An example is `enumeratePhysicalDevices`.

```haskell
enumeratePhysicalDevices
  :: MonadIO m => Instance -> m (Result, Vector PhysicalDevice)

```

--------------------------------

### Construct Vulkan Struct Chain with Pattern Synonyms

Source: https://hackage.haskell.org/package/vulkan

Demonstrates how to create a Vulkan instance creation info structure with extensions like debug utils and validation features using the `:&` and `()` pattern synonyms to build a struct chain.

```haskell
makeInst = do
  let debugCreateInfo = _ :: DebugUtilsMessengerCreateInfoEXT
      validationFeatures = ValidationFeaturesEXT [VALIDATION_FEATURE_ENABLE_BEST_PRACTICES_EXT] []
      instanceCreateInfo = zero ::& debugCreateInfo :& validationFeatures :& ()
  createInstance instanceCreateInfo Nothing
```

--------------------------------

### Build Vulkan Packages with Nix

Source: https://hackage.haskell.org/package/vulkan

Commands to build specific components of the repository using the Nix build tool.

```bash
nix-build -A vulkan
nix-build -A vulkan-examples
```

--------------------------------

### Parsing Enums and Bitmasks in Haskell

Source: https://hackage.haskell.org/package/vulkan

Demonstrates how to use the `Read` and `Show` instances for Vulkan enums and bitmasks in Haskell to parse pattern synonyms. This allows for convenient conversion between string representations and their corresponding Haskell types.

```haskell
read @COMPARE_OP "COMPARE_OP_LESS"

```

--------------------------------

### Evaluate Nix Attribute Set

Source: https://hackage.haskell.org/package/vulkan

Evaluates the default.nix file to expose the available package set including vulkan, VMA bindings, and utility functions.

```nix
default.nix { forShell = false; }
```

--------------------------------

### Run Generator Program

Source: https://hackage.haskell.org/package/vulkan

Executes the generator program within a configured shell environment to produce Vulkan source code.

```bash
ghci $(HIE_BIOS_OUTPUT=/dev/stdout ./flags.sh $(pwd)/vk/Main.hs) vk/Main.hs +RTS -N16
```

--------------------------------

### Deconstruct Vulkan Struct Chain to Check Features

Source: https://hackage.haskell.org/package/vulkan

Shows how to extract specific features, like Timeline Semaphores, from a Vulkan struct chain returned by `getPhysicalDeviceFeatures2` using pattern matching with `:&` and `()`.

```haskell
hasTimelineSemaphores phys = do
  _ ::& PhysicalDeviceTimelineSemaphoreFeatures hasTimelineSemaphores :& () <- 
    getPhysicalDeviceFeatures2 phys
  pure hasTimelineSemaphores
```

```haskell
hasTimelineSemaphores phys = do
  feats <- getPhysicalDeviceFeatures2 phys
  let _ ::& PhysicalDeviceTimelineSemaphoreFeatures hasTimelineSemaphores :& ()
       = feats
  pure hasTimelineSemaphores
```

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