Strict extension does not make monadic bindings strict

The following two programs are not equivalent with respect to the strictness of readFile:

{-# LANGUAGE BangPatterns #-}

module Main where

main = do
  !contents <- readFile "foo.txt"
  print contents

And:

{-# LANGAUGE Strict #-}

module Main where

main = do
  contents <- readFile "foo.txt"
  print contents

Inspecting GHC Core for these two programs suggests that

!contents <- readFile "foo.txt"

is not equivalent to (with Strict enabled):

contents <- readFile "foo.txt"

Here's core using BangPatterns:

(readFile (unpackCString# "foo.txt"#))
(\ (contents_asg :: String) ->
   case contents_asg of contents1_Xsk { __DEFAULT ->
   print @ String $dShow_rYy contents1_Xsk
   })

Here's core using Strict:

(readFile (unpackCString# "foo.txt"#))
(\ (contents_asg :: String) ->
   print @ String $dShow_rYv contents_asg)

Does this core align with the design of the Strict extension? If it does, are users going to understand that using Strict is going to make let/where bindings strict, but is not going to make >>= bindings strict?

However, this is likely to just be a bug. At least, Johan Tibell and Adam Sandberg Eriksson, the designers and implementers of the Strict extension, believe this to be a bug:

Johan Tibell @ Thu Dec 10 14:34:39 UTC 2015 writes:

I believe this is just a bug, since the desugaring ought to be strict in the \x.

https://mail.haskell.org/pipermail/ghc-devs/2015-December/010747.html

Adam Sandberg Eriksson @ Thu Dec 10 15:26:17 UTC 2015 writes:

I agree that this seems to be a bug. I have a lot to do currently, but might be able to look at it sometime during next week.

https://mail.haskell.org/pipermail/ghc-devs/2015-December/010749.html

Trac metadata

Trac field	Value
Version	7.11
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (CodeGen)
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