(* ast.sml
 *
 * COPYRIGHT (c) 2010 The Diderot Project (http://diderot-language.cs.uchicago.edu)
 * All rights reserved.
 *
 * A typed abstract-syntax tree representation of Diderot programs.
 *)

structure AST =
  struct

    structure Ty = Types

  (* AST variable kinds *)
    datatype var_kind
      = BasisVar
      | InputVar
      | GlobalVar
      | StrandParam		(* parameter to strand definition *)
      | StrandStateVar		(* strand state variable *)
      | StrandOutputVar		(* strand output variable *)
      | LocalVar		(* local variable in method *)

    datatype var = V of {
	name : string,		(* print name of variable *)
	id : Stamp.stamp,	(* unique ID *)
	kind : var_kind,	(* variable kind *)
	ty : Ty.scheme		(* type scheme *)
      }

    datatype program
      = Program of decl list

    and decl
      = D_Input of var * expr option
      | D_Var of var_decl			(* global variable decl *)
      | D_Strand of {				(* strand decl *)
	    name : Atom.atom,
	    params : var list,
	    state : var_decl list,		(* true marks output variables *)
	    methods : method list
	  }
      | D_InitialArray of create * iter list
      | D_InitialCollection of create * iter list

    and var_decl
      = VD_Decl of var * expr

    and method
      = M_Method of Atom.atom * stmt

    and create
      = C_Create of (Atom.atom * expr list)

    and iter
    (* NOTE: the typechecker restricts the variable and expression to have integer type *)
      = I_Range of var * expr * expr

    and stmt
      = S_Block of stmt list
      | S_Decl of var_decl
      | S_IfThenElse of expr * stmt * stmt
      | S_Assign of var * expr
      | S_New of Atom.atom * expr list
      | S_Die
      | S_Stabilize

    and expr
      = E_Var of var
      | E_Lit of Literal.literal
      | E_Tuple of expr list
      | E_Apply of var * Ty.meta_var list * expr list * Ty.ty
		(* note: operators can be polymorphic, so we record the type arguments. *)
      | E_Cons of expr list				(* tensor-value construction *)
      | E_Slice of expr * expr option list * Ty.ty	(* tensor slicing *)
      | E_Cond of expr * expr * expr * Ty.ty		(* ty is result type *)

  end

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	<div class="error">does not end with &lt;/html&gt; tag</div>
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	<div class="info">The output has ended thus: ty	(* tensor slicing *)
      | E_Cond of expr * expr * expr * Ty.ty		(* ty is result type *)

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