Ogre type system.
Ogre type system is extremely simple, it has only four types: 1. boolean - a logical type that has only two values (true,false); 2. int - an integral number that maps to OCaml's int64; 3. float - a real number that maps to OCaml's float; 4. str - an arbitrary string, represented as string in OCaml.
A scheme is a first class value, that describes how to construct attributes from fields, and how to deconstruct them.
A field is a pair of a name and a type, and is used to reference to construct attributes, and to reference to attribute objects in queries.
val int : int64 tint is represented with OCaml's int64, and has a corresponding representation
val bool : bool tbool is either true or false.
val str : string tstr represented by a sequence of characters. If the sequence contains whitespaces or parenthesis then the sequence should be delimited with quotes. Note, the requirements are for the database backend implementations. A user of the library shouldn't be bothered by the representation.
val float : float tscheme field defines a scheme with one field.
scm $field adds a field to a scheme scm.
Usually, all the fields are combined in a one expression, starting with the call to a function scheme, e.g.,
scheme name $ age $ salary
The scheme had type (('a -> 'r) -> 'r, ('a -> 'p) -> 'p) scheme, then the type of a resulting scheme would be [(('a -> 'b -> 'r) -> 'r, ('a ->
'b -> 'p) -> 'p) scheme], i.e., a type of $field will be attached to the scheme.
For example, the scheme name $age $salary expression will have a type (assuming, that name, age and salary are represented with string, int, and int, correspondingly):
(string -> int64 -> int64 -> 'a) -> 'a,
(string -> int64 -> int64 -> 'b) -> 'bThe scheme is used to construct an attribute. See below.