Given that CI only seems to test against GHC 7.10 & GHC 8.0 it's safe to say that only
`base >= 4.8` is officially supported. And empirically, GHC 7.8.4 runs into the compile error below
```
Configuring component lib from esqueleto-2.5.0...
Preprocessing library esqueleto-2.5.0...
[1 of 5] Compiling Database.Esqueleto.Internal.PersistentImport ( src/Database/Esqueleto/Internal/PersistentImport.hs, /tmp/matrix-worker/1485112890/dist-newstyle/build/x86_64-linux/ghc-7.8.4/esqueleto-2.5.0/build/Database/Esqueleto/Internal/PersistentImport.o )
src/Database/Esqueleto/Internal/PersistentImport.hs:7:1: Warning:
The import item ‘PersistQuery(..)’ suggests that
‘PersistQuery’ has (in-scope) constructors or class methods,
but it has none
[2 of 5] Compiling Database.Esqueleto.Internal.Language ( src/Database/Esqueleto/Internal/Language.hs, /tmp/matrix-worker/1485112890/dist-newstyle/build/x86_64-linux/ghc-7.8.4/esqueleto-2.5.0/build/Database/Esqueleto/Internal/Language.o )
src/Database/Esqueleto/Internal/Language.hs:55:1: Warning:
The qualified import of ‘Data.ByteString.Lazy’ is redundant
except perhaps to import instances from ‘Data.ByteString.Lazy’
To import instances alone, use: import Data.ByteString.Lazy()
[3 of 5] Compiling Database.Esqueleto.Internal.Sql ( src/Database/Esqueleto/Internal/Sql.hs, /tmp/matrix-worker/1485112890/dist-newstyle/build/x86_64-linux/ghc-7.8.4/esqueleto-2.5.0/build/Database/Esqueleto/Internal/Sql.o )
src/Database/Esqueleto/Internal/Sql.hs:761:32:
Could not deduce (Functor m1) arising from a use of ‘<$>’
from the context (SqlSelect a r, MonadIO m1, MonadIO m2)
bound by the type signature for
rawSelectSource :: (SqlSelect a r, MonadIO m1, MonadIO m2) =>
Mode -> SqlQuery a -> SqlReadT m1 (Acquire (C.Source m2 r))
at src/Database/Esqueleto/Internal/Sql.hs:(753,20)-(758,57)
or from (SqlBackendCanRead backend)
bound by the type signature for
rawSelectSource :: (SqlBackendCanRead backend) =>
Mode
-> SqlQuery a -> R.ReaderT backend m1 (Acquire (C.Source m2 r))
at src/Database/Esqueleto/Internal/Sql.hs:(759,1)-(778,35)
Possible fix:
add (Functor m1) to the context of
the type signature for
rawSelectSource :: (SqlBackendCanRead backend) =>
Mode
-> SqlQuery a -> R.ReaderT backend m1 (Acquire (C.Source m2 r))
or the type signature for
rawSelectSource :: (SqlSelect a r, MonadIO m1, MonadIO m2) =>
Mode -> SqlQuery a -> SqlReadT m1 (Acquire (C.Source m2 r))
In a stmt of a 'do' block: conn <- persistBackend <$> R.ask
In the expression:
do { conn <- persistBackend <$> R.ask;
res <- run conn;
return $ (C.$= massage) `fmap` res }
In an equation for ‘rawSelectSource’:
rawSelectSource mode query
= do { conn <- persistBackend <$> R.ask;
res <- run conn;
return $ (C.$= massage) `fmap` res }
where
run conn
= uncurry rawQueryRes
$ first builderToText
$ toRawSql mode (conn, initialIdentState) query
massage
= do { mrow <- C.await;
.... }
process = sqlSelectProcessRow
src/Database/Esqueleto/Internal/Sql.hs:882:26:
Could not deduce (Functor m) arising from a use of ‘<$>’
from the context (MonadIO m, SqlSelect a r, IsSqlBackend backend)
bound by the type signature for
rawEsqueleto :: (MonadIO m, SqlSelect a r, IsSqlBackend backend) =>
Mode -> SqlQuery a -> R.ReaderT backend m Int64
at src/Database/Esqueleto/Internal/Sql.hs:(877,17)-(880,39)
Possible fix:
add (Functor m) to the context of
the type signature for
rawEsqueleto :: (MonadIO m, SqlSelect a r, IsSqlBackend backend) =>
Mode -> SqlQuery a -> R.ReaderT backend m Int64
In a stmt of a 'do' block: conn <- persistBackend <$> R.ask
In the expression:
do { conn <- persistBackend <$> R.ask;
uncurry rawExecuteCount
$ first builderToText
$ toRawSql mode (conn, initialIdentState) query }
In an equation for ‘rawEsqueleto’:
rawEsqueleto mode query
= do { conn <- persistBackend <$> R.ask;
uncurry rawExecuteCount
$ first builderToText
$ toRawSql mode (conn, initialIdentState) query }
```
