[GHC] #12508: Show evaluation step-by-step in GHCi

[GHC]

#12508: Show evaluation step-by-step in GHCi
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           Reporter:  Hi-Angel       |             Owner:
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:
          Component:  GHCi           |           Version:  8.0.1
           Keywords:  interactive    |  Operating System:  Unknown/Multiple
  evaluation debugging               |
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 The ability see every evaluation step for executing a particular code in
 ghci is needed.

 Earlier that could have [[http://stackoverflow.com/a/554391/2388257|done
 in HAT]], or ghc-vis. But as of today, HAT doesn't compile even with
 stack. And, at least personally for me, neither ghc-vis could be
 installed.

 I want to point out that the funcionality is **very** important for the
 language. Without that ''(i.e. as it is now)'' it is impossible for
 newcomers to see how a particular construction going to be evaluated, how
 much memory it going to take. Nowadays newcomers have to deal with memory
 issues post-mortem: an app takes all system memory, dies, then one build
 everything for profiling, and start playing a Battleship with the
 allocation graph; which going to be a hard game, unless you're experienced
 enough to not even allow that to happen most of the times.

 However, if there was a way to execute functions in GHCI, looking the
 evaluation step-by-step, days of hard debugging would turn into a few
 hours of executing a couple of functions in ghci.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12508>
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