Re: [GHC] #15422: GHCi debugger doesn't see free variables when using ApplicativeDo

20 Jul 2018


      #15422: GHCi debugger doesn't see free variables when using ApplicativeDo
-------------------------------------+-------------------------------------
        Reporter:  simonmar          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.4.3
      Resolution:                    |             Keywords:  ApplicativeDo
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4991
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Description changed by simonmar:

Old description:
...
```
...
ghci break029.hs
GHCi, version 8.2.2: http://www.haskell.org/ghc/  :? for help
[1 of 1] Compiling Main             ( break029.hs, interpreted )
Ok, one module loaded.
*Main> :!cat break029.hs
{-# LANGUAGE ApplicativeDo #-}
f :: Int -> IO Int
f x = do
  y <- return (x + 1)
  return (y * 2)
*Main> :step f 3
Stopped in Main.f, break029.hs:(4,7)-(6,16)
_result :: IO Int = _
x :: Int = 3
[break029.hs:(4,7)-(6,16)] [break029.hs:(4,7)-(6,16)] *Main> :list
3  f :: Int -> IO Int
4  f x = do
5    y <- return (x + 1)
6    return (y * 2)
7
[break029.hs:(4,7)-(6,16)] [break029.hs:(4,7)-(6,16)] *Main> :step
Stopped in Main.f, break029.hs:5:8-21
_result :: IO Int = _
x :: Int = 3
[break029.hs:5:8-21] [break029.hs:5:8-21] *Main> :list
4  f x = do
5    y <- return (x + 1)
6    return (y * 2)
[break029.hs:5:8-21] [break029.hs:5:8-21] *Main> :step
Stopped in Main.f, break029.hs:6:11-15
_result :: Int = _
[break029.hs:6:11-15] [break029.hs:6:11-15] *Main> y
<interactive>:7:1: error: Variable not in scope: y
```
New description:

 {{{
...
ghci break029.hs
 GHCi, version 8.2.2: http://www.haskell.org/ghc/  :? for help
 [1 of 1] Compiling Main             ( break029.hs, interpreted )
 Ok, one module loaded.
 *Main> :!cat break029.hs
 {-# LANGUAGE ApplicativeDo #-}
f :: Int -> IO Int
 f x = do
   y <- return (x + 1)
   return (y * 2)
 *Main> :step f 3
 Stopped in Main.f, break029.hs:(4,7)-(6,16)
 _result :: IO Int = _
 x :: Int = 3
 [break029.hs:(4,7)-(6,16)] [break029.hs:(4,7)-(6,16)] *Main> :list
 3  f :: Int -> IO Int
 4  f x = do
 5    y <- return (x + 1)
 6    return (y * 2)
 7
 [break029.hs:(4,7)-(6,16)] [break029.hs:(4,7)-(6,16)] *Main> :step
 Stopped in Main.f, break029.hs:5:8-21
 _result :: IO Int = _
 x :: Int = 3
 [break029.hs:5:8-21] [break029.hs:5:8-21] *Main> :list
 4  f x = do
 5    y <- return (x + 1)
 6    return (y * 2)
 [break029.hs:5:8-21] [break029.hs:5:8-21] *Main> :step
 Stopped in Main.f, break029.hs:6:11-15
 _result :: Int = _
 [break029.hs:6:11-15] [break029.hs:6:11-15] *Main> y

 <interactive>:7:1: error: Variable not in scope: y
 }}}

--

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15422#comment:1
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