ghc doesn't seem to be unifying deriveJSON (String->String) parameter with id :: a -> a. examples/TemplateHaskell.hs:22:14: Couldn't match expected type `Data.Aeson.TH.Options' with actual type `a0 -> a0' In the first argument of `deriveJSON', namely `id' In the expression: deriveJSON id ''Coord ghc --make: /usr/hs/ghc/7.4.1/bin/ghc failure (return code=1) ghc-7.4.1 x86_64 Centos-6 [jim@localhost aeson]$ ghc-pkg list --package-conf=../cabal-dev/packages-7.4.1.conf ../cabal-dev/packages-7.4.1.conf HTTP-4000.2.6 aeson-0.6.1.0 attoparsec-0.10.3.0 attoparsec-conduit-0.5.0.3 base-unicode-symbols-0.2.2.4 blaze-builder-0.3.1.0 blaze-builder-conduit-0.5.0.3 case-insensitive-0.4.0.4 conduit-0.5.6 dlist-0.5 hashable-1.2.0.5 http-types-0.7.3.0.1 lifted-base-0.2.0.2 monad-control-0.3.1.4 nats-0.1 network-2.4.1.0 network-conduit-0.6.2.2 parsec-3.1.3 primitive-0.5.0.1 resourcet-0.4.4 semigroups-0.9 simple-sendfile-0.2.10 transformers-base-0.4.1 unix-compat-0.4.1.0 unordered-containers-0.2.3.0 vault-0.2.0.4 vector-0.10.0.1 void-0.5.11 wai-1.3.0.1 warp-1.3.7.1