The command :show bindings works for let a = 1:

Prelude> let a = 1
Prelude> :show bindings
a :: Num p => p = _

But not for a = 1:

Prelude> a = 1
Prelude> :show bindings
ghc-stage2.exe: ^^ Could not load 'interactive_Ghci1_zdtrModule2_closure', dependency unresolved. See top entry above.

ghc-stage2.exe: ^^ Could not load 'interactive_Ghci1_zdtrModule4_closure', dependency unresolved. See top entry above.

$trModule :: GHC.Types.Module = _
$trModule1 :: GHC.Types.TrName = _
$trModule2 ::
  GHC.Prim.Addr# = *** Exception:
ByteCodeLink.lookupCE
During interactive linking, GHCi couldn't find the following symbol:
  interactive_Ghci1_zdtrModule2_closure
This may be due to you not asking GHCi to load extra object files,
archives or DLLs needed by your current session.  Restart GHCi, specifying
the missing library using the -L/path/to/object/dir and -lmissinglibname
flags, or simply by naming the relevant files on the GHCi command line.
Alternatively, this link failure might indicate a bug in GHCi.
If you suspect the latter, please send a bug report to:
  glasgow-haskell-bugs@haskell.org

$trModule3 :: GHC.Types.TrName = _
$trModule4 ::
  GHC.Prim.Addr# = *** Exception:
ByteCodeLink.lookupCE
During interactive linking, GHCi couldn't find the following symbol:
  interactive_Ghci1_zdtrModule4_closure
This may be due to you not asking GHCi to load extra object files,
archives or DLLs needed by your current session.  Restart GHCi, specifying
the missing library using the -L/path/to/object/dir and -lmissinglibname
flags, or simply by naming the relevant files on the GHCi command line.
Alternatively, this link failure might indicate a bug in GHCi.
If you suspect the latter, please send a bug report to:
  glasgow-haskell-bugs@haskell.org

a :: Num p => p = _
a1 :: Integer = _