Haskell process command errored with: (error "Unexpected response from haskell process.")

[Abhiroop]

A Haskell project which builds fine with stack build runs into this issue.

Unexpected response from haskell process.
Haskell process command errored with: (error "Unexpected response from haskell process.")

No helpful error messages to debug too.

[identicalsnowflake]

I just upgraded to GHC 8.2.1 and suddenly I'm getting this, too. My project builds fine (no stack involved), but emacs mode is broken - C-c C-l gives the error you posted.

EDIT: Downgrading to GHC 8.0.2 causes this error to go away.

[gracjan]

This is related: #1168

[Abhiroop]

The issue was solved for me when I :set -fobject-code in GHCi. This issue can be closed now, if its solved for @identicalsnowflake

[identicalsnowflake]

Where are you setting this? I tried entering :set -fobject-code in ghci directly as well as putting it in my .ghci file in my home directory, but I still get the unexpected response error.

[Abhiroop]

This error message might be a common message for different class of errors(I am not sure about this).
For me I faced it while compiling https://github.com/typelead/eta
Setting object code in GHCi worked for me. And I was on GHC 7.10.

[identicalsnowflake]

Hmm. In my case I don't think it's a package: I get it even on the default "Hello world" file generated by cabal init.

[peti]

This is a duplicate of #1553.

[nrolland]

I am confronted to this message. How can we debug that to get more information on what's failing ?

[Abhiroop]

@nrolland This seems like a common catch all error clause whose occurrence entirely depends on the code that you are trying to load. Like mentioned above my issue was solved by setting :set -fobject-code, but it is not necessary that the same will work with you.

I faced the same warning when I was trying to load a program with unlifted types. So you would have to produce a snippet of the program you are trying to load to debug it.

[nrolland]

@Abhiroop yeah, and since it's generic I imagined there was some "debug" facility to get more info to activate somewhere.

There is an haskell-process-log emacs variable which creates a buffer but that seems to be OK, my module is loaded.

How did you come up with your idea of setting :set -fobject-code ?

[nrolland]

For potential future references, there seems to be a bunch of heuristics in haskell-load.el in haskell-process-load-complete on how to interpret the response (found by C-h f haskell-process-load-file , reading the source, and repeating the process )

Replacing the function haskell-process-consume which does the matching to

(defun haskell-process-consume (process regex)
  "Consume a regex from the response and move the cursor along if succeed."
  (progn
    (haskell-process-log (format "process: %S\n" (haskell-process-response process)))
    (haskell-process-log (format "regex: %s\n" regex))
  (when (string-match regex
                      (haskell-process-response process)
                      (haskell-process-response-cursor process))
    (haskell-process-set-response-cursor process (match-end 0))
    t)))

and eval-defun this, one can then see in *haskell-process-log*, after loading a file

-> :load "/Users/nrolland/Sync/mactoastyClones/xquant2/content/notes/typerole/src/Examples.hs"
<- [1 of 1] Compiling Examples ( /Users/nrolland/Sync/mactoastyClones/xquant2/content/notes/typerole/src/Examples.hs, interpreted )
Ok, one module loaded.
Collecting type info for 1 module(s) ...
�
process: "[1 of 1] Compiling Examples ( /Users/nrolland/Sync/mactoastyClones/xquant2/content/notes/typerole/src/Examples.hs, interpreted )
Ok, one module loaded.
Collecting type info for 1 module(s) ...
�"

regex: [[ ]([0-9]+) of ([0-9]+)] Compiling ([^ ]+)[ ]+( ([^ ]+), ([^ ]+) )[^][
]+

process: "[1 of 1] Compiling Examples ( /Users/nrolland/Sync/mactoastyClones/xquant2/content/notes/typerole/src/Examples.hs, interpreted )
Ok, one module loaded.
Collecting type info for 1 module(s) ...
�"

regex: [[ ]([0-9]+) of ([0-9]+)] Compiling ([^ ]+)[ ]+( ([^ ]+), ([^ ]+) )[^][
]+

process: "[1 of 1] Compiling Examples ( /Users/nrolland/Sync/mactoastyClones/xquant2/content/notes/typerole/src/Examples.hs, interpreted )
Ok, one module loaded.
Collecting type info for 1 module(s) ...
�"

regex: [[ ]([0-9]+) of ([0-9]+)] Compiling [TH] ([^ ]+)[ ]+( ([^ ]+), ([^ ]+) )[^][
]+

process: "[1 of 1] Compiling Examples ( /Users/nrolland/Sync/mactoastyClones/xquant2/content/notes/typerole/src/Examples.hs, interpreted )
Ok, one module loaded.
Collecting type info for 1 module(s) ...
�"

regex: Loading package ([^ ]+) ... linking ... done.

process: "[1 of 1] Compiling Examples ( /Users/nrolland/Sync/mactoastyClones/xquant2/content/notes/typerole/src/Examples.hs, interpreted )
Ok, one module loaded.
Collecting type info for 1 module(s) ...
�"

regex: ^Preprocessing executables for (.+?)...

process: "[1 of 1] Compiling Examples ( /Users/nrolland/Sync/mactoastyClones/xquant2/content/notes/typerole/src/Examples.hs, interpreted )
Ok, one module loaded.
Collecting type info for 1 module(s) ...
�"

regex: Linking (.+?) ...

process: "[1 of 1] Compiling Examples ( /Users/nrolland/Sync/mactoastyClones/xquant2/content/notes/typerole/src/Examples.hs, interpreted )
Ok, one module loaded.
Collecting type info for 1 module(s) ...
�"

regex:
Building (.+?)...

process: "[1 of 1] Compiling Examples ( /Users/nrolland/Sync/mactoastyClones/xquant2/content/notes/typerole/src/Examples.hs, interpreted )
Ok, one module loaded.
Collecting type info for 1 module(s) ...
�"

regex: Ok, (?:[0-9]+) modules? loaded.$

process: "[1 of 1] Compiling Examples ( /Users/nrolland/Sync/mactoastyClones/xquant2/content/notes/typerole/src/Examples.hs, interpreted )
Ok, one module loaded.
Collecting type info for 1 module(s) ...
�"

regex: Failed, (?:[0-9]+) modules? loaded.$

process: "[1 of 1] Compiling Examples ( /Users/nrolland/Sync/mactoastyClones/xquant2/content/notes/typerole/src/Examples.hs, interpreted )
Ok, one module loaded.
Collecting type info for 1 module(s) ...
�"

regex: Ok, modules loaded: (.+).$

process: "[1 of 1] Compiling Examples ( /Users/nrolland/Sync/mactoastyClones/xquant2/content/notes/typerole/src/Examples.hs, interpreted )
Ok, one module loaded.
Collecting type info for 1 module(s) ...
�"

regex: Failed, modules loaded: (.+).$

This was probably intended to match

process: "[1 of 1] Compiling Examples ( /Users/nrolland/Sync/mactoastyClones/xquant2/content/notes/typerole/src/Examples.hs, interpreted )
Ok, one module loaded.
Collecting type info for 1 module(s) ...
�"

regex: Ok, (?:[0-9]+) modules? loaded.$

Notice "one" in the response VS "1" in the match

[GeorgeCo]

I'm seeing this issue on ghc 8.4.3 with the latest version of haskell-mode, without stack. haskell-process-log shows:

:set prompt2 "λ| "
...
�Some flags have not been recognized: prompt2

The issue seems to be that the code is using ":set prompt2" instead of :set prompt-cont as adamse points out in #1569. This can be verified in ghci:

λ> :set prompt2 "λ| "
Some flags have not been recognized: prompt2, λ|
λ> :set prompt-cont "λ| "
λ>

I changed the code to set prompt-cont rather than prompt2 which got rid of the error above but does not seem to fix the reported issue although the error message seems irrelevant as the code does get loaded (which may even have been true before I made that change in the .el files on my machine). This issue seems like it is being fixed in #1605