rA.ml

   1 (*
   2  Relational Algebra
   3 *)
   4
   5 open ListMore
   6 open Printf
   7 open Operators
   8
   9 module Type = Sql.Type
  10
  11 type attr = {name : string; domain : Type.t;}
  12   deriving (Show)
  13
  14 let attr n d = {name=n;domain=d}
  15
  16 module Scheme =
  17 struct
  18   type t = attr list
  19     deriving (Show)
  20
  21   exception Error of t * string
  22
  23   let find t name =
  24     match List.find_all (fun attr -> attr.name = name) t with
  25     | [x] -> x
  26     | [] -> raise (Error (t,"missing attribute : " ^ name))
  27     | _ -> raise (Error (t,"duplicate attribute : " ^ name))
  28
  29   let is_unique t =
  30     let t1 = List.unique ~cmp:(fun a1 a2 -> a1.name = a2.name && a1.name <> "") t in
  31     List.length t1 = List.length t
  32
  33   let check_unique t = is_unique t || raise (Error (t,"duplicate attributes"))
  34
  35   let project names t = List.map (find t) names
  36
  37   let rename t before after =
  38     List.map (fun attr ->
  39       match attr.name with
  40       | x when x = before -> { attr with name=after }
  41       | _ -> attr ) t
  42
  43   let cross t1 t2 = t1 @ t2
  44
  45   (** [contains t attr] tests whether schema [t] contains attribute [attr] *)
  46   let contains t attr = find t attr.name = attr
  47
  48   let check_contains t attr =
  49     if not (contains t attr) then
  50       raise (Error (t,"type mismatch for attribute " ^ attr.name))
  51
  52   let sub l a = List.filter (fun x -> not (List.mem x a)) l
  53
  54   let to_string v = Show.show<t>(v)
  55   let names t = t >> List.map (fun attr -> attr.name) >> String.concat "," >> sprintf "[%s]"
  56
  57   let natural_ t1 t2 =
  58     let (common,t1only) = List.partition (fun x -> List.mem x t2) t1 in
  59     if 0 = List.length common then failwith "natural'";
  60     let t2only = sub t2 common in
  61     common @ t1only @ t2only
  62
  63   let natural t1 t2 =
  64     try natural_ t1 t2 with
  65     | _ -> raise (Error (t1,"no common attributes for natural join of " ^
  66                              (names t1) ^ " and " ^ (names t2)))
  67
  68   let join_using l t1 t2 =
  69     let common = List.map (find t1) l in
  70     List.iter (check_contains t2) common;
  71     common @ sub t1 common @ sub t2 common
  72
  73   (* FIXME? should be less strict -- check only types *)
  74   let compound t1 t2 =
  75     if t1 <> t2 then
  76       raise (Error (t1, (to_string t1) ^ " not equal to " ^ (to_string t2)))
  77      else
  78       t1
  79
  80   let to_string x = Show.show<t>(x)
  81   let print x = prerr_endline (to_string x)
  82
  83 end
  84
  85 type table = string * Scheme.t deriving (Show)
  86
  87 let print_table t = print_endline (Show.show<table>(t))
  88
  89 (*
  90 open Scheme
  91
  92 let test = [{name="a";domain=Type.Int}; {name="b";domain=Type.Int}; {name="c";domain=Type.Text};];;
  93
  94 let () = print test
  95 let () = print (project ["b";"c";"b"] test)
  96 let () = print (project ["b";"d"] test)
  97 let () = print (rename test "a" "new_a")
  98 *)