Should nextval :: QualifiedName -> Expr Int64 support more numeric types?

[raehik]

9.17. Sequence Manipulation Functions in the Postgres docs state that nextval returns a bigint, which matches with Rel8's nextval :: QualifiedName -> Expr Int64. However, the CREATE SEQUENCE page states:

The optional clause AS data_type specifies the data type of the sequence. [...] The data type determines the default minimum and maximum values of the sequence.

To me, this means the type of nextval is dependent on the sequence it's accessing. Similar to DEFAULT, that's probably not very useful for Rel8. But it is confusing: the codebase I'm poking at has many nextval functions like fooIdNextval = coerce (Rel8.nextval "foo_id_seq"). Sometimes they're coercing through both a newtype and Expr's phantom typevar at the same time. (Should Rel8 even permit coerceExpr :: Expr a -> Expr b; coerceExpr = coerce? It does. Note the lack of Coercible!)

I think this is especially relevant because the serial pseudo-type often used together with nextval corresponds to an Int32, but currently to use them together in Rel8 a user must coerce down from Int64. (I think this may have been a source of confusion in our codebase: there is a mix of Int32 and Int64 IDs that use serial in the table schema, where Int32 is surely more correct. It definitely confused me, heh.)

I don't really have an answer in mind or a specific request. (I'm also new to Rel8 and SQL in general.) Has anyone else felt this issue? Is there something I'm missing? I think a newtype PostgresSerial and a few nextval helpers would help us stay consistent, but I wonder if there's a library-level solution too.

[raehik]

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