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1. data CallStack

   base	GHC.Exception

   CallStacks are a lightweight method of obtaining a partial call-stack at any point in the program. A function can request its call-site with the HasCallStack constraint. For example, we can define

   putStrLnWithCallStack :: HasCallStack => String -> IO ()
   

   as a variant of putStrLn that will get its call-site and print it, along with the string given as argument. We can access the call-stack inside putStrLnWithCallStack with callStack.

   >>> :{
   putStrLnWithCallStack :: HasCallStack => String -> IO ()
   putStrLnWithCallStack msg = do
   putStrLn msg
   putStrLn (prettyCallStack callStack)
   :}
   

   Thus, if we call putStrLnWithCallStack we will get a formatted call-stack alongside our string.

   >>> putStrLnWithCallStack "hello"
   hello
   CallStack (from HasCallStack):
   putStrLnWithCallStack, called at <interactive>:... in interactive:Ghci...
   

   GHC solves HasCallStack constraints in three steps:
   1. If there is a CallStack in scope -- i.e. the enclosing function has a HasCallStack constraint -- GHC will append the new call-site to the existing CallStack.
   2. If there is no CallStack in scope -- e.g. in the GHCi session above -- and the enclosing definition does not have an explicit type signature, GHC will infer a HasCallStack constraint for the enclosing definition (subject to the monomorphism restriction).
   3. If there is no CallStack in scope and the enclosing definition has an explicit type signature, GHC will solve the HasCallStack constraint for the singleton CallStack containing just the current call-site.
   CallStacks do not interact with the RTS and do not require compilation with -prof. On the other hand, as they are built up explicitly via the HasCallStack constraints, they will generally not contain as much information as the simulated call-stacks maintained by the RTS. A CallStack is a [(String, SrcLoc)]. The String is the name of function that was called, the SrcLoc is the call-site. The list is ordered with the most recently called function at the head. NOTE: The intrepid user may notice that HasCallStack is just an alias for an implicit parameter ?callStack :: CallStack. This is an implementation detail and should not be considered part of the CallStack API, we may decide to change the implementation in the future.

2. data ErrorCall

   base	GHC.Exception

   This is thrown when the user calls error. The first String is the argument given to error, second String is the location.

3. pattern ErrorCall :: String -> ErrorCall

   base	GHC.Exception

   No documentation available.

4. ErrorCallWithLocation :: String -> String -> ErrorCall

   base	GHC.Exception

   No documentation available.

5. errorCallException :: String -> SomeException

   base	GHC.Exception

   No documentation available.

6. errorCallWithCallStackException :: String -> CallStack -> SomeException

   base	GHC.Exception

   No documentation available.

7. fromCallSiteList :: [([Char], SrcLoc)] -> CallStack

   base	GHC.Exception

   Convert a list of call-sites to a CallStack.

8. getCallStack :: CallStack -> [([Char], SrcLoc)]

   base	GHC.Exception

   Extract a list of call-sites from the CallStack. The list is ordered by most recent call.

9. prettyCallStack :: CallStack -> String

   base	GHC.Exception

   Pretty print a CallStack.

10. prettyCallStackLines :: CallStack -> [String]

    base	GHC.Exception

    No documentation available.

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