Inferring result schemas from a Definition.

[echatav]

A neat fact is that we can infer the resulting schema from a Definition. The resulting SchemasType is pretty ugly looking, consisting of partly evaluated and partly unevaluated type families & synonyms. Let's see an example:

>>> :{
let
  setup :: Definition (Public '[]) _
  setup =
    createTable #users
      ( serial `as` #id :*
        (text & notNullable) `as` #name )
      ( primaryKey #id `as` #pk_users ) >>>
    createTable #emails
      ( serial `as` #id :*
        (int & notNullable) `as` #user_id :*
        (text & nullable) `as` #email )
      ( primaryKey #id `as` #pk_emails :*
        foreignKey #user_id #users #id
          (OnDelete Cascade) (OnUpdate Cascade) `as` #fk_user_id )
:}

<interactive>:78:36: error:
    • Found type wildcard ‘_’
        standing for ‘'["public"
                        ::: ('("users",
                               'Table
                                 ('["pk_users" ::: 'PrimaryKey '["id"]]
                                  :=> '["id" ::: '( 'Def, 'NotNull 'PGint4),
                                        "name" ::: '( 'NoDef, 'NotNull 'PGtext)]))
                               : Create
                                   "emails"
                                   ('Table
                                      ('["pk_emails" ::: 'PrimaryKey '["id"],
                                         "fk_user_id"
                                         ::: 'ForeignKey '["user_id"] "public" "users" '["id"]]
                                       :=> '["id" ::: '( 'Def, 'NotNull 'PGint4),
                                             "user_id" ::: '( 'NoDef, 'NotNull 'PGint4),
                                             "email" ::: '( 'NoDef, 'Null 'PGtext)]))
                                   '[])] :: [(Symbol,
                                              [(Symbol, SchemumType)])]’
      To use the inferred type, enable PartialTypeSignatures
    • In the second argument of ‘Definition’, namely ‘_’
      In the type ‘Definition (Public '[]) _’
      In the type signature: setup :: Definition (Public '[]) _