Panic! make_exp (App _ (Coercion _)) when compiled with -fext-core

[EduardSergeev]

An attempt to compile the attached file with 7.6.2 (and 7.4.2) with "-O2 -fext-core" leads to:

ghc: panic! (the 'impossible' happened)
  (GHC version 7.6.2 for x86_64-unknown-linux):
    make_exp (App _ (Coercion _))

[EduardSergeev]

Compile me with "-O2 -fext-core"

[simonpj]

Indeed. In MkExternalCore we see:

make_exp (App _e (Coercion _co)) = error "make_exp (App _ (Coercion _))"    -- TODO

Generally, External Core lacks a proper treatment of the coercions of Core.

Does anyone feel like looking at this? It's pretty straightforward:

• The External Core data type
• Concrete syntax
• Parsing
• Pretty printing
• Conversion to and from Core

Generally, External Core could do with some love.

Simon

[mvanier]

I got the same compiler panic with ghc 7.4.2 on Mac OS X 10.6.8 with this trivial file:

-- Begin file "Main.hs".
-- Compile with "ghc -fext-core Main.hs"
module Main where

main :: IO ()
main = print 10
-- End file.

Curiously, it doesn't panic when the main = print 10 line is changed to main = print "10".

[simonpj]

Just to re-iterate, there is no technical problem here, just a need for someone who cares about External Core to decide what syntax to use, extend the data type etc. Volunteers?

Simon