[1 of 3] Compiling T12042[boot]     ( T12042.hs-boot, T12042.o-boot )
[2 of 3] Compiling T12042a          ( T12042a.hs, T12042a.o )
[3 of 3] Compiling T12042           ( T12042.hs, T12042.o )

T12042.hs-boot:2:1: error:
    Type constructor ‘S’ has conflicting definitions in the module
    and its hs-boot file
    Main module: type S :: *
                 type S = R
    Boot file:   type S :: *
                 data S