EncodeParams describes an encoding of a Haskell Type into a list of parameter NullTypes.

>>> conn <- connectdb @'[] "host=localhost port=5432 dbname=exampledb"
>>> :{
let
  encode :: EncodeParams '[]
    '[ 'NotNull 'PGint2, 'NotNull ('PGchar 1), 'NotNull 'PGtext]
    (Int16, (Char, String))
  encode = fst .* fst.snd *. snd.snd
in runReaderT (runEncodeParams encode (1,('a',"foo"))) conn
:}
K (Just "\NUL\SOH") :* K (Just "a") :* K (Just "foo") :* Nil

>>> finish conn

Parameter encoding for Generic tuples and records.

>>> import qualified GHC.Generics as GHC
>>> import qualified Generics.SOP as SOP
>>> data Two = Two Int16 String deriving (GHC.Generic, SOP.Generic)
>>> conn <- connectdb @'[] "host=localhost port=5432 dbname=exampledb"
>>> :{
let
  encode :: EncodeParams '[] '[ 'NotNull 'PGint2, 'NotNull 'PGtext] Two
  encode = genericParams
in runReaderT (runEncodeParams encode (Two 2 "two")) conn
:}
K (Just "\NUL\STX") :* K (Just "two") :* Nil

>>> :{
let
  encode :: EncodeParams '[] '[ 'NotNull 'PGint2, 'NotNull 'PGtext] (Int16, String)
  encode = genericParams
in runReaderT (runEncodeParams encode (2, "two")) conn
:}
K (Just "\NUL\STX") :* K (Just "two") :* Nil

>>> finish conn

Encode 0 parameters.

Cons a parameter encoding.

>>> conn <- connectdb @'[] "host=localhost port=5432 dbname=exampledb"
>>> :{
let
  encode :: EncodeParams '[]
    '[ 'Null 'PGint4, 'NotNull 'PGtext]
    (Maybe Int32, String)
  encode = fst .* snd .* nilParams
in runReaderT (runEncodeParams encode (Nothing, "foo")) conn
:}
K Nothing :* K (Just "foo") :* Nil

>>> finish conn

End a parameter encoding.

>>> conn <- connectdb @'[] "host=localhost port=5432 dbname=exampledb"
>>> :{
let
  encode :: EncodeParams '[]
    '[ 'Null 'PGint4, 'NotNull 'PGtext, 'NotNull ('PGchar 1)]
    (Maybe Int32, String, Char)
  encode = (\(x,_,_) -> x) .* (\(_,y,_) -> y) *. (\(_,_,z) -> z)
in runReaderT (runEncodeParams encode (Nothing, "foo", 'z')) conn
:}
K Nothing :* K (Just "foo") :* K (Just "z") :* Nil

>>> finish conn

Encode 1 parameter.

>>> conn <- connectdb @'[] "host=localhost port=5432 dbname=exampledb"
>>> :{
let
  encode :: EncodeParams '[] '[ 'NotNull 'PGint4] Int32
  encode = aParam
in runReaderT (runEncodeParams encode 1776) conn
:}
K (Just "\NUL\NUL\ACK\240") :* Nil

>>> finish conn

Append parameter encodings.

>>> conn <- connectdb @'[] "host=localhost port=5432 dbname=exampledb"
>>> :{
let
  encode :: EncodeParams '[]
    '[ 'NotNull 'PGint4, 'NotNull 'PGint2]
    (Int32, Int16)
  encode = contramap fst aParam `appendParams` contramap snd aParam
in runReaderT (runEncodeParams encode (1776, 2)) conn
:}
K (Just "\NUL\NUL\ACK\240") :* K (Just "\NUL\STX") :* Nil

>>> finish conn

A ToPG constraint gives an encoding of a Haskell Type into into the binary format of a PostgreSQL PGType.

A ToParam constraint gives an encoding of a Haskell Type into into the binary format of a PostgreSQL NullType. You should not define instances for ToParam, just use the provided instances.

A ToField constraint lifts the ToPG parser to an encoding of a (Symbol, Type) to a (Symbol, NullityType), encoding Nulls to Maybes. You should not define instances for ToField, just use the provided instances.

A ToArray constraint gives an encoding of a Haskell Type into the binary format of a PostgreSQL fixed-length array. You should not define instances for ToArray, just use the provided instances.