Test of GHC debugger with GHC 9.2

ghci.txt

ghci> :l ~/TestDebug.hs 
[1 of 1] Compiling Main             ( /home/guillaume/TestDebug.hs, interpreted )
Ok, one module loaded.
ghci> -- Let's add a breakpoint in go
ghci> :break fact.go
Breakpoint 0 activated at /home/guillaume/TestDebug.hs:8:16-23
Breakpoint 1 activated at /home/guillaume/TestDebug.hs:(9,17)-(11,26)
ghci> :trace fact 10
Stopped in Main.fact.go, /home/guillaume/TestDebug.hs:(9,17)-(11,26)
_result :: IO Int = _
acc :: Int = 1
n :: Int = 10
[/home/guillaume/TestDebug.hs:(9,17)-(11,26)] ghci> :set stop :list
[/home/guillaume/TestDebug.hs:(9,17)-(11,26)] ghci> -- I've just set :list each time I stop at a breakpoint, that's convenient.
[/home/guillaume/TestDebug.hs:(9,17)-(11,26)] ghci> :continue
Yada
Stopped in Main.fact.go, /home/guillaume/TestDebug.hs:(9,17)-(11,26)
_result :: IO Int = _
acc :: Int = 10
n :: Int = 9
8      go acc 0 = pure acc
9      go !acc n = do
10        putStrLn "Yada"
11        go (acc * n) (n - 1)
12  
[/home/guillaume/TestDebug.hs:(9,17)-(11,26)] ghci> :continue
Yada
Stopped in Main.fact.go, /home/guillaume/TestDebug.hs:(9,17)-(11,26)
_result :: IO Int = _
acc :: Int = 90
n :: Int = 8
8      go acc 0 = pure acc
9      go !acc n = do
10        putStrLn "Yada"
11        go (acc * n) (n - 1)
12  
[/home/guillaume/TestDebug.hs:(9,17)-(11,26)] ghci> -- we can inspect values
[/home/guillaume/TestDebug.hs:(9,17)-(11,26)] ghci> n
8
[/home/guillaume/TestDebug.hs:(9,17)-(11,26)] ghci> acc
90
[/home/guillaume/TestDebug.hs:(9,17)-(11,26)] ghci> :step
Stopped in Main.fact.go, /home/guillaume/TestDebug.hs:10:7-21
_result :: IO () = _
9      go !acc n = do
10        putStrLn "Yada"
11        go (acc * n) (n - 1)
[/home/guillaume/TestDebug.hs:10:7-21] ghci> :step
Yada
Stopped in Main.fact.go, /home/guillaume/TestDebug.hs:11:7-26
_result :: IO Int = _
acc :: Int = 90
n :: Int = 8
10        putStrLn "Yada"
11        go (acc * n) (n - 1)
12  
[/home/guillaume/TestDebug.hs:11:7-26] ghci> :step
Stopped in Main.fact.go, /home/guillaume/TestDebug.hs:11:21-25
_result :: Int = _
n :: Int = 8
10        putStrLn "Yada"
11        go (acc * n) (n - 1)
12  
[/home/guillaume/TestDebug.hs:11:21-25] ghci> -- Here we saw sub expression evaluation
[/home/guillaume/TestDebug.hs:11:21-25] ghci> :force _result
_result = 7
[/home/guillaume/TestDebug.hs:11:21-25] ghci> :step
Stopped in Main.fact.go, /home/guillaume/TestDebug.hs:11:11-17
_result :: Int = _
acc :: Int = 90
n :: Int = 8
10        putStrLn "Yada"
11        go (acc * n) (n - 1)
12  
[/home/guillaume/TestDebug.hs:11:11-17] ghci> :step
Stopped in Main.fact.go, /home/guillaume/TestDebug.hs:(9,17)-(11,26)
_result :: IO Int = _
acc :: Int = 720
n :: Int = 7
8      go acc 0 = pure acc
9      go !acc n = do
10        putStrLn "Yada"
11        go (acc * n) (n - 1)
12  
[/home/guillaume/TestDebug.hs:(9,17)-(11,26)] ghci> :step
Stopped in Main.fact.go, /home/guillaume/TestDebug.hs:10:7-21
_result :: IO () = _
9      go !acc n = do
10        putStrLn "Yada"
11        go (acc * n) (n - 1)
[/home/guillaume/TestDebug.hs:10:7-21] ghci> :step
Yada
Stopped in Main.fact.go, /home/guillaume/TestDebug.hs:11:7-26
_result :: IO Int = _
acc :: Int = 720
n :: Int = 7
10        putStrLn "Yada"
11        go (acc * n) (n - 1)
12  
[/home/guillaume/TestDebug.hs:11:7-26] ghci> -- we can also skip N times
[/home/guillaume/TestDebug.hs:11:7-26] ghci> :continue 4
Stopped in Main.fact.go, /home/guillaume/TestDebug.hs:(9,17)-(11,26)
_result :: IO Int = _
acc :: Int = 5040
n :: Int = 6
8      go acc 0 = pure acc
9      go !acc n = do
10        putStrLn "Yada"
11        go (acc * n) (n - 1)
12  
[/home/guillaume/TestDebug.hs:(9,17)-(11,26)] ghci> :continue 20
Yada
Yada
Yada
Yada
Yada
Stopped in Main.fact.go, /home/guillaume/TestDebug.hs:11:7-26
_result :: IO Int = _
acc :: Int = 1814400
n :: Int = 2
10        putStrLn "Yada"
11        go (acc * n) (n - 1)
12  
[/home/guillaume/TestDebug.hs:11:7-26] ghci> -- We can inspect history
[/home/guillaume/TestDebug.hs:11:7-26] ghci> :history
-1  : fact:go (/home/guillaume/TestDebug.hs:(9,17)-(11,26))
-2  : fact:go (/home/guillaume/TestDebug.hs:11:7-26)
-3  : fact:go (/home/guillaume/TestDebug.hs:10:7-21)
-4  : fact:go (/home/guillaume/TestDebug.hs:(9,17)-(11,26))
-5  : fact:go (/home/guillaume/TestDebug.hs:11:11-17)
-6  : fact:go (/home/guillaume/TestDebug.hs:11:21-25)
-7  : fact:go (/home/guillaume/TestDebug.hs:11:7-26)
-8  : fact:go (/home/guillaume/TestDebug.hs:10:7-21)
-9  : fact:go (/home/guillaume/TestDebug.hs:(9,17)-(11,26))
-10 : fact:go (/home/guillaume/TestDebug.hs:(9,17)-(11,26))
-11 : fact:go (/home/guillaume/TestDebug.hs:(9,17)-(11,26))
-12 : fact (/home/guillaume/TestDebug.hs:6:8-11)
<end of history>
[/home/guillaume/TestDebug.hs:11:7-26] ghci> -- and we can even have a look back in history
[/home/guillaume/TestDebug.hs:11:7-26] ghci> :back 
Logged breakpoint at /home/guillaume/TestDebug.hs:(9,17)-(11,26)
_result :: IO Int
acc :: Int
n :: Int
8      go acc 0 = pure acc
9      go !acc n = do
10        putStrLn "Yada"
11        go (acc * n) (n - 1)
12  
[-1: /home/guillaume/TestDebug.hs:(9,17)-(11,26)] ghci> :back 
Logged breakpoint at /home/guillaume/TestDebug.hs:11:7-26
_result :: IO Int
acc :: Int
n :: Int
10        putStrLn "Yada"
11        go (acc * n) (n - 1)
12  
[-2: /home/guillaume/TestDebug.hs:11:7-26] ghci> :back 
Logged breakpoint at /home/guillaume/TestDebug.hs:10:7-21
_result :: IO ()
9      go !acc n = do
10        putStrLn "Yada"
11        go (acc * n) (n - 1)
[-3: /home/guillaume/TestDebug.hs:10:7-21] ghci> :back 
Logged breakpoint at /home/guillaume/TestDebug.hs:(9,17)-(11,26)
_result :: IO Int
acc :: Int
n :: Int
8      go acc 0 = pure acc
9      go !acc n = do
10        putStrLn "Yada"
11        go (acc * n) (n - 1)
12  
[-4: /home/guillaume/TestDebug.hs:(9,17)-(11,26)] ghci> :back 
Logged breakpoint at /home/guillaume/TestDebug.hs:11:11-17
_result :: Int
acc :: Int
n :: Int
10        putStrLn "Yada"
11        go (acc * n) (n - 1)
12  
[-5: /home/guillaume/TestDebug.hs:11:11-17] ghci> :back 
Warning: _result has been evaluated, some bindings have been lost
Logged breakpoint at /home/guillaume/TestDebug.hs:11:21-25
_result :: t
10        putStrLn "Yada"
11        go (acc * n) (n - 1)
12  
[-6: /home/guillaume/TestDebug.hs:11:21-25] ghci> :back 
Logged breakpoint at /home/guillaume/TestDebug.hs:11:7-26
_result :: IO Int
acc :: Int
n :: Int
10        putStrLn "Yada"
11        go (acc * n) (n - 1)
12  
[-7: /home/guillaume/TestDebug.hs:11:7-26] ghci> :back 
Logged breakpoint at /home/guillaume/TestDebug.hs:10:7-21
_result :: IO ()
9      go !acc n = do
10        putStrLn "Yada"
11        go (acc * n) (n - 1)
[-8: /home/guillaume/TestDebug.hs:10:7-21] ghci> :step
Stopped in Main.fact.go, /home/guillaume/TestDebug.hs:11:21-25
_result :: Int = _
n :: Int = 2
10        putStrLn "Yada"
11        go (acc * n) (n - 1)
12  
[/home/guillaume/TestDebug.hs:11:21-25] ghci> :history
-1  : fact:go (/home/guillaume/TestDebug.hs:11:7-26)
-2  : fact:go (/home/guillaume/TestDebug.hs:(9,17)-(11,26))
-3  : fact:go (/home/guillaume/TestDebug.hs:11:7-26)
-4  : fact:go (/home/guillaume/TestDebug.hs:10:7-21)
-5  : fact:go (/home/guillaume/TestDebug.hs:(9,17)-(11,26))
-6  : fact:go (/home/guillaume/TestDebug.hs:11:11-17)
-7  : fact:go (/home/guillaume/TestDebug.hs:11:21-25)
-8  : fact:go (/home/guillaume/TestDebug.hs:11:7-26)
-9  : fact:go (/home/guillaume/TestDebug.hs:10:7-21)
-10 : fact:go (/home/guillaume/TestDebug.hs:(9,17)-(11,26))
-11 : fact:go (/home/guillaume/TestDebug.hs:(9,17)-(11,26))
-12 : fact:go (/home/guillaume/TestDebug.hs:(9,17)-(11,26))
-13 : fact (/home/guillaume/TestDebug.hs:6:8-11)
<end of history>
[/home/guillaume/TestDebug.hs:11:21-25] ghci> :forward
already at the beginning of the history
[/home/guillaume/TestDebug.hs:11:21-25] ghci> :contiue
unknown command ':contiue'
use :? for help.
[/home/guillaume/TestDebug.hs:11:21-25] ghci> :continue
Yada
Stopped in Main.fact.go, /home/guillaume/TestDebug.hs:11:7-26
_result :: IO Int = _
acc :: Int = 3628800
n :: Int = 1
10        putStrLn "Yada"
11        go (acc * n) (n - 1)
12  
[/home/guillaume/TestDebug.hs:11:7-26] ghci> :continue
Stopped in Main.fact.go, /home/guillaume/TestDebug.hs:8:16-23
_result :: IO t = _
acc :: t = _
7    where
8      go acc 0 = pure acc
9      go !acc n = do
[/home/guillaume/TestDebug.hs:8:16-23] ghci> :history
-1  : fact:go (/home/guillaume/TestDebug.hs:11:7-26)
-2  : fact:go (/home/guillaume/TestDebug.hs:11:21-25)
-3  : fact:go (/home/guillaume/TestDebug.hs:11:7-26)
-4  : fact:go (/home/guillaume/TestDebug.hs:(9,17)-(11,26))
-5  : fact:go (/home/guillaume/TestDebug.hs:11:7-26)
-6  : fact:go (/home/guillaume/TestDebug.hs:10:7-21)
-7  : fact:go (/home/guillaume/TestDebug.hs:(9,17)-(11,26))
-8  : fact:go (/home/guillaume/TestDebug.hs:11:11-17)
-9  : fact:go (/home/guillaume/TestDebug.hs:11:21-25)
-10 : fact:go (/home/guillaume/TestDebug.hs:11:7-26)
-11 : fact:go (/home/guillaume/TestDebug.hs:10:7-21)
-12 : fact:go (/home/guillaume/TestDebug.hs:(9,17)-(11,26))
-13 : fact:go (/home/guillaume/TestDebug.hs:(9,17)-(11,26))
-14 : fact:go (/home/guillaume/TestDebug.hs:(9,17)-(11,26))
-15 : fact (/home/guillaume/TestDebug.hs:6:8-11)
<end of history>
[/home/guillaume/TestDebug.hs:8:16-23] ghci> :back 15
Logged breakpoint at /home/guillaume/TestDebug.hs:6:8-11
_result :: Int -> IO Int
5  fact :: Int -> IO Int
6  fact = go 1
7    where
[-15: /home/guillaume/TestDebug.hs:6:8-11] ghci> :force _result
_result = _
[-15: /home/guillaume/TestDebug.hs:6:8-11] ghci> -- haha, that's fun
[-15: /home/guillaume/TestDebug.hs:6:8-11] ghci> :continue
3628800

TestDebug.hs

{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE BangPatterns #-}
import Control.Arrow

fact :: Int -> IO Int
fact = go 1
  where
    go acc 0 = pure acc
    go !acc n = do
      putStrLn "Yada"
      go (acc * n) (n - 1)

main = do
  mapM_ (\n -> print =<< fact n) [0..100]