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Summary

GHCi hangs when setting a breakpoint in an eta reduced function and re-evaluating this function when the breakpoint is hit.

Steps to reproduce

Use the module Hang.hs:

module Hang where

foo :: Int -> Int
foo = bar

bar :: Int -> Int
bar n = 2 * n

Do the following steps:

ghci Hang.hs
:break foo
foo 1              -- Evaluate function foo. GHCi stops at breakpoint
foo 2              -- Re-evaluate function foo from the breakpoint

-> GHCi now hangs!

Expected behavior

GHCi should not hang, it should stop at a nested breakpoint

Note

When I remove the eta reduction in the function foo

foo :: Int -> Int
foo x = bar x

then everything works fine!

Environment

• GHC version used: 7.10.3 - 8.10.2 and HEAD

Optional:

• Operating System: Debian 9
• System Architecture: x86-64