The Clod monad

This monad stack combines:

• Reader for dependency injection of ClodConfig
• Error handling with ExceptT for ClodError
• IO for filesystem, git, and other side effects

This replaces the previous effects-based approach with a simpler, more traditional monad stack.

Errors that can occur during Clod operation

These represent the different categories of errors that can occur during file processing, allowing for specific error handling for each case.

Configuration for the clod program

Run a ClodM computation, returning either an error or a result

Is used within a monadic computation to begin exception processing.

A handler function to handle previous errors and return to normal execution. A common idiom is:

do { action1; action2; action3 } `catchError` handler

where the action functions can call throwError. Note that handler and the do-block must have the same return type.

Lift a computation from the IO monad. This allows us to run IO computations in any monadic stack, so long as it supports these kinds of operations (i.e. IO is the base monad for the stack).

Example

import Control.Monad.Trans.State -- from the "transformers" library

printState :: Show s => StateT s IO ()
printState = do
  state <- get
  liftIO $ print state

• Couldn't match type ‘IO’ with ‘StateT s IO’
 Expected type: StateT s IO ()
   Actual type: IO ()

> evalStateT printState "hello"
"hello"

> evalStateT printState 3
3

Retrieves the monad environment.

Retrieves a function of the current environment.

Executes a computation in a modified environment.