如何在Haskell中打印调用栈？求助解决实现失败问题

Let’s walk through why your current approach isn’t working and how to fix it:

Why Your Current Methods Aren’t Producing Output #

• traceStack: This function only appends a stack trace when an exception is thrown. Since putStrLn doesn’t throw an error, nothing gets logged here.
• emptyCallStack: As the name suggests, this is an empty stack—calling getCallStack on it will always return an empty list.
• currentCallStack: Without proper function annotations or compiler flags, this might return an incomplete or empty stack because GHC isn’t tracking the necessary stack info.

Required Compiler & Runtime Setup #

First, update your .cabal file’s ghc-options for the executable to include these flags (in addition to -fprof-auto):

ghc-options:
  -fprof-auto
  -rtsopts
  -fprof-cafs

• -rtsopts: Lets you pass runtime system (RTS) options when running the program.
• -fprof-cafs: Enables profiling of constant applicative forms, which helps capture more complete stack traces.

When running HLS, use this command to ensure profiling is active and stack traces are enabled:

cabal run haskell-language-server-wrapper --enable-profiling --enable-executable-dynamic +RTS -xc

• +RTS -xc: Forces GHC to print a stack trace whenever an exception is thrown—great for debugging crashes.

Corrected Code to Print Call Stacks #

Modify your defaultMain function to use GHC’s proper call stack utilities. You’ll need to import GHC.Stack and add a HasCallStack constraint:

import GHC.Stack (HasCallStack, callStack, getCallStack, currentCallStack, traceStack)

defaultMain :: HasCallStack => Recorder (WithPriority Log) -> Arguments -> IdePlugins IdeState -> IO ()
defaultMain recorder args idePlugins = do
    -- Print stack using the HasCallStack annotation
    putStrLn "=== Call stack from HasCallStack ==="
    mapM_ print $ getCallStack callStack

    -- Print current stack via IO
    putStrLn "\n=== Current runtime call stack ==="
    stack <- currentCallStack
    mapM_ putStrLn stack

    -- Trigger a stack trace with traceStack (requires an exception)
    putStrLn "\n=== Exception stack trace ==="
    _ <- traceStack "Error context" $ error "Intentional error to show stack trace"
    exitFailure

Key Fixes: #

• HasCallStack constraint: This tells GHC to track the call stack up to defaultMain, making the callStack variable available.
• getCallStack callStack: Uses the actual stack from the current context instead of an empty one.
• Exception with traceStack: By throwing an error, you trigger traceStack to log the stack trace.

Extra Tips #

• If stacks are still incomplete, make sure all dependencies are built with profiling. Run this to rebuild everything with profiling flags:

  cabal build --enable-profiling --enable-executable-dynamic --ghc-options="-fprof-auto"
  

• Remember to remove profiling flags for production builds, as they add overhead.

内容的提问来源于stack exchange，提问作者zichao liu