(* typechecker.sml
 *
 * COPYRIGHT (c) 2010 The Diderot Project (http://diderot.cs.uchicago.edu)
 * All rights reserved.
 *)

structure Typechecker : sig

    val check : ParseTree.program -> AST.program

  end = struct

    structure PT = ParseTree
    structure Ty = Types

  (* check a differentiation level, which muse be >= 0 *)
    fun checkDiff (cxt, k) =
	  if (k < 0)
	    then raise Fail "differentiation must be >= 0"
	    else Ty.DiffConst(IntInf.toInt k)

  (* check a dimension, which must be 2 or 3 *)
    fun checkDim (cxt, d) =
	  if (d < 2) orelse (3 < d)
	    then raise Fail "invalid dimension; must be 2 or 3"
	    else Ty.DimConst(IntInf.toInt d)

  (* check a shape *)
    fun checkShape (cxt, shape) = let
	  fun chkDim d = if (d < 1)
		then raise Fail "invalid shape dimension; must be >= 1"
		else Ty.DimConst(IntInf.toInt d)
	  in
	    Ty.Shape(List.map chkDim shape)
	  end

  (* check the well-formedness of a type and translate it to an AST type *)
    fun checkTy (cxt, ty) = (case ty
	   of PT.T_Mark m => checkTy(#span m, #tree m)
	    | PT.T_Bool => Ty.T_Bool
	    | PT.T_Int => Ty.T_Int
	    | PT.T_Real => Ty.realTy
	    | PT.T_String => Ty.T_String
	    | PT.T_Vec n => (* NOTE: the parser guarantees that 2 <= n <= 4 *)
		Ty.vecTy(IntInf.toInt n)
	    | PT.T_Kernel k => Ty.T_Kernel(checkDiff(cxt, k))
	    | PT.T_Field{diff, dim, shape} => Ty.T_Field{
		  diff = checkDiff (cxt, diff),
		  dim = checkDim (cxt, dim),
		  shape = checkShape (cxt, shape)
		}
	    | PT.T_Tensor shape => Ty.T_Tensor(checkShape(cxt, shape))
	    | PT.T_Image{dim, shape} => Ty.T_Image{
		  dim = checkDim (cxt, dim),
		  shape = checkShape (cxt, shape)
		}
	    | PT.T_Array(ty, dims) => raise Fail "Array type"
	  (* end case *))

    fun checkLit lit = (case lit
	   of (Literal.Int _) => (AST.E_Lit lit, Ty.T_Int)
	    | (Literal.Float _) => (AST.E_Lit lit, Ty.realTy)
	    | (Literal.String s) => (AST.E_Lit lit, Ty.T_String)
	    | (Literal.Bool _) => (AST.E_Lit lit, Ty.T_Bool)
	  (* end case *))

(*
  (* typecheck an expression and translate it to AST *)
    fun checkExpr (env, cxt, e) = (case e
	   of PT.E_Mark m => checkExpr (env, #span m, #tree m)
	    | PT.E_Var x => (case Env.findVar (env, x)
		 of SOME x' => (case Var.typeOf x'
		       of ([], ty) => (AST.E_Var x', ty)
			| scheme => let
			    val (args, ty) = Util.instantiate scheme
			    in
			      (AST.E_VarInst(x', args, ty), ty)
			    end
		      (* end case *))
		  | NONE => raise Fail "undefined variable"
		(* end case *))
	    | PT.E_Lit lit => checkLit lit
	    | PT.E_BinOp of expr * var * expr
	    | PT.E_UnaryOp of var * expr
	    | PT.E_Tuple of expr list
	    | PT.E_Apply of var * expr list
	    | PT.E_Cons of ty * expr list
	  (* end case *))

    fun checkVarDecl (env, cxt, kind, d) = (case d
	   of PT.VD_Mark m => checkVarDecl (env, #span m, kind, #tree m)
	    | PT.VD_Decl(ty, x, e) => let
		val ty = checkType ty
		val x' = Var.new (x, kind, ty)
		val (e', ty') = checkExpr (env, cxt, e)
		in
(* FIXME: check types *)
		  AST.VD_Decl(x', e')
		end
	  (* end case *))

  (* typecheck a statement and translate it to AST *)
    fun checkStmt (env, cxt, s) = (case s
	   of PT.S_Mark m => checkStmt (env, #span m, #tree m)
	    | PT.S_Block stms => let
		fun chk (_, [], stms) = AST.S_Block(List.rev stms)
		  | chk (env, s::ss, stms) = let
		      val (s', env') = checkStmt (env, cxt, s)
		      in
			chk (env', ss, s'::ss)
		      end
		in
		  (chk (env, stms, []), env)
		end
	    | PT.S_Decl vd => let
		val vd as AST.VD_Decl(x, _) = checkVarDecl (env, cxt, Var.LocalVar, vd)
		in
		  (AST.S_Decl vd, Env.insertLocal(env, x, x'))
		end
	    | PT.S_IfThen(e, s) => let
		val (e', ty) = checkExpr (env, cxt, e)
		val s' = checkStmt (env, cxt, s)
		in
		(* check that condition has bool type *)
		  case ty
		   of Ty.T_Bool => ()
		    | _ => raise Fail "condition not boolean type"
		  (* end case *);
		  (AST.S_IfThenElse(e', s', AST.S_Block[]), env)
		end
	    | PT.S_IfThenElse(e, s1, s2) => let
		val (e', ty) = checkExpr (env, cxt, e)
		val s1' = checkStmt (env, cxt, s1)
		val s2' = checkStmt (env, cxt, s2)
		in
		(* check that condition has bool type *)
		  case ty
		   of Ty.T_Bool => ()
		    | _ => raise Fail "condition not boolean type"
		  (* end case *);
		  (AST.S_IfThenElse(e', s1', s2'), env)
		end
	    | PT.S_Assign(x, e) => (case Env.findVar (env, x)
		 of NONE => raise Fail "undefined variable"
		  | SOME x' => let
		      val (e', ty) = checkExpr (env, cxt, e)
		      in
(* FIXME: check types *)
		      (* check that x' is mutable *)
			case Var.kindOf x'
			 of Var.ActorStateVar => ()
			  | Var.LocalVar => ()
			  | _ => raise Fail "assignment to immutable variable"
			(* end case *);
			(AST.S_Assign(x', e'), env)
		      end
		(* end case *))
	    | PT.S_New(actor, args) => let
		val argTys' = List.map (fn e => checkExpr(env, cxt, e)) args
		val (args', tys') = ListPair.unzip argTys'
		in
(* FIXME: check that actor is defined and has the argument types match *)
		  AST.S_New(actor, args')
		end
	    | PT.S_Die => (AST.S_Die, env)
	    | PT.S_Stabilize => (AST.S_Stabilize, env)
	  (* end case *))

    fun checkDecl (env, cxt, d) = (case d
	   of PT.D_Mark m => checkDecl (env, #span m, #tree m)
	    | PT.D_Input(ty, x, optExp) => let
		val ty = checkTy(cxt, ty)
		val x' = Var.new(x, Var.InputVar, ty)
		val dcl = (case optExp
		       of NONE => AST.D_Input(x', NONE)
			| SOME e => let
			    val (e', ty') = checkExpr (env, cxt, e)
			    in
(* FIXME: check types *)
			      AST.D_Input(x', SOME e')
			    end
		      (* end case *))
		in
		  (dcl, Env.insertGlobal(env, x, x'))
		end
	    | PT.D_Var vd => let
		val vd as AST.VD_Decl(x, _) = checkVarDecl (env, cxt, Var.GlobalVar, vd)
		in
		  (AST.D_Var vd, Env.insertGlobal(env, x, x'))
		end
	    | PT.D_Actor{nam, params, state, methods} => ??
	    | PT.D_InitialArray of create * iter list
	    | PT.D_InitialCollection of create * iter list
	  (* end case *))
*)

    fun check (PT.Program dcls) = AST.Program[]

  end