In which case, I've created a ticket to record this bug and to track its fix:

https://ghc.haskell.org/trac/ghc/ticket/11193

On 10 December 2015 at 15:26, Adam Sandberg Eriksson <adam@sandbergericsson.se> wrote:
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.
 
Adam Sandberg Eriksson
 
 
On Thu, 10 Dec 2015, at 03:34 PM, Johan Tibell wrote:
I believe this is just a bug, since the desugaring ought to be strict in the \x.
 
On Tue, Dec 8, 2015 at 6:35 PM, Ömer Sinan Ağacan <omeragacan@gmail.com> wrote:
I think this is a problem/bug in the implementation. In the "function
definitions" section of the wiki page it says the argument will have a
bang pattern. But then this code:
 
    do x <- ...
       return (x + 1)
 
which is just a syntactic sugar for `... >>= \x -> return (x + 1)`
doesn't have the bang pattern in `x`.
 
(See also a related email I sent to ghc-devs yesterday:
 
2015-12-08 12:27 GMT-05:00 David Kraeutmann <kane@kane.cx>:
> While there's a fundamental difference between (>>=) and let-bindings, it
> might be worth adding to the docs that -XStrict only makes let bindings
> strict.
>
>
> On 12/08/2015 06:22 PM, Rob Stewart wrote:
>
> Are the following two programs equivalent with respect to the strictness
> of `readFile`?
>
> --8<---------------cut here---------------start------------->8---
> {-# LANGUAGE BangPatterns #-}
>
> module Main where
>
> main = do
>   !contents <- readFile "foo.txt"
>   print contents
> --8<---------------cut here---------------end--------------->8---
>
> And:
>
> --8<---------------cut here---------------start------------->8---
> {-# LANGAUGE Strict #-}
>
> module Main where
>
> main = do
>   contents <- readFile "foo.txt"
>   print contents
> --8<---------------cut here---------------end--------------->8---
>
> The documentation on "Strict-by-default pattern bindings" gives
> let/where binding as an example, but there is not a monadic bind example.
>
> 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 <- or >>=
> bindings strict?
>
> --
> Rob Stewart
>
>
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> ghc-devs mailing list
>
>
>
> _______________________________________________
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>
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