:l shell.hs
:def shell (\s -> do shell s; return "")

-- We have this structure of modules:

-- A (imports B.boot)
-- B (imports A)
-- B.boot (imports A)
-- C (imports A and B)

-- And we load C, to debug some function in A which enters B.
-- But first we touch A, and reload. B.boot will be reloaded, but not B,  which will end up with an empty modbreaks. When we :step into B, ghci will die with an out of bounds access in B's break array.
-- The effect we want is B.boot being reloaded while B is not.

:shell cp A1.hs A.hs
:l C
:shell echo >> A.hs
:r
:break a
a ()
:st
:st -- here we step into B, and produce the exception