Felipe Almeida Lessa wrote:

What are those messages?

Messages resulting from a single incorrect identifier below. I actually now notice that error for line 76 point to the specific cause, while the multiple errors flagged for line 62 just confuse matters. Part of the confusion is that I tend to look at error messages from top to bottom, possibly from my long term work in C and C++. I'm not sure if the top to bottom approach to reading error messages is valid for Haskell. Cheers, Erik blog.hs:62:15: Couldn't match type `SqlPersist' with `SqlPersist IO (PersonGeneric SqlPersist)' When using functional dependencies to combine Database.Esqueleto.Internal.Sql.SqlSelect (SqlExpr (Entity a)) (Entity a), arising from the dependency `a -> r' in the instance declaration in `Database.Esqueleto.Internal.Sql' Database.Esqueleto.Internal.Sql.SqlSelect (SqlExpr (Entity (PersonGeneric SqlPersist))) (Entity (SqlPersist IO (SqlPersist IO (PersonGeneric SqlPersist)))), arising from a use of `select' at blog.hs:62:15-20 In the expression: select In a stmt of a 'do' block: people <- select $ from $ \ p -> do { where_ (p ^. PersonAge >=. val age); return p } blog.hs:62:15: Couldn't match type `PersonGeneric' with `SqlPersist IO' When using functional dependencies to combine Database.Esqueleto.Internal.Sql.SqlSelect (SqlExpr (Entity a)) (Entity a), arising from the dependency `a -> r' in the instance declaration in `Database.Esqueleto.Internal.Sql' Database.Esqueleto.Internal.Sql.SqlSelect (SqlExpr (Entity (PersonGeneric SqlPersist))) (Entity (SqlPersist IO (SqlPersist IO (PersonGeneric SqlPersist)))), arising from a use of `select' at blog.hs:62:15-20 In the expression: select In a stmt of a 'do' block: people <- select $ from $ \ p -> do { where_ (p ^. PersonAge >=. val age); return p } blog.hs:62:15: Couldn't match type `SqlPersist IO (PersonGeneric SqlPersist)' with `SqlPersist' When using functional dependencies to combine Database.Esqueleto.Internal.Sql.SqlSelect (SqlExpr (Entity a)) (Entity a), arising from the dependency `r -> a' in the instance declaration in `Database.Esqueleto.Internal.Sql' Database.Esqueleto.Internal.Sql.SqlSelect (SqlExpr (Entity (PersonGeneric SqlPersist))) (Entity (SqlPersist IO (SqlPersist IO (PersonGeneric SqlPersist)))), arising from a use of `select' at blog.hs:62:15-20 In the expression: select In a stmt of a 'do' block: people <- select $ from $ \ p -> do { where_ (p ^. PersonAge >=. val age); return p } blog.hs:62:15: Couldn't match type `SqlPersist IO' with `PersonGeneric' When using functional dependencies to combine Database.Esqueleto.Internal.Sql.SqlSelect (SqlExpr (Entity a)) (Entity a), arising from the dependency `r -> a' in the instance declaration in `Database.Esqueleto.Internal.Sql' Database.Esqueleto.Internal.Sql.SqlSelect (SqlExpr (Entity (PersonGeneric SqlPersist))) (Entity (SqlPersist IO (SqlPersist IO (PersonGeneric SqlPersist)))), arising from a use of `select' at blog.hs:62:15-20 In the expression: select In a stmt of a 'do' block: people <- select $ from $ \ p -> do { where_ (p ^. PersonAge >=. val age); return p } blog.hs:76:32: Couldn't match expected type `PersonGeneric backend0' with actual type `BlogPostGeneric backend1' Expected type: EntityField (PersonGeneric backend0) a0 Actual type: EntityField (BlogPostGeneric backend1) String In the second argument of `(^.)', namely `BlogPostTitle' In the first argument of `asc', namely `(b ^. BlogPostTitle)' -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/