open Sexplib.Std

(** Literal values for Const nodes *)
type value =
  | Int   of int
  | Float of float
  | Str   of string
  | Bool  of bool
[@@deriving sexp]

type direction = Asc | Desc
[@@deriving sexp]

type query =
  | Base    of string                          (** base relation by name *)
  | Const   of (string * value) list           (** constant single-tuple relation *)
  | Select  of query * query                   (** σ semijoin: (filter, source) *)
  | Join    of string list * query * query     (** ⋈ natural equijoin on named attrs *)
  | Cartesian of query * query                 (** × Cartesian product *)
  | Project of string list * query             (** π restrict columns *)
  | Rename  of (string * string) list * query  (** ρ rename (old,new) pairs *)
  | Union   of query * query                   (** ∪ — compatible schemas assumed *)
  | Diff    of query * query                   (** − *)
  | Take    of int * query                     (** τ *)
[@@deriving sexp]