catala/compiler/dcalc/ast.mli

(* This file is part of the Catala compiler, a specification language for tax
   and social benefits computation rules. Copyright (C) 2020 Inria, contributor:
   Denis Merigoux <denis.merigoux@inria.fr>, Alain Delaët-Tixeuil
   <alain.delaet--tixeuil@inria.fr>

   Licensed under the Apache License, Version 2.0 (the "License"); you may not
   use this file except in compliance with the License. You may obtain a copy of
   the License at

   http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
   License for the specific language governing permissions and limitations under
   the License. *)

(** Abstract syntax tree of the default calculus intermediate representation *)

open Utils
module ScopeName : Uid.Id with type info = Uid.MarkedString.info
module StructName : Uid.Id with type info = Uid.MarkedString.info
module StructFieldName : Uid.Id with type info = Uid.MarkedString.info
module StructMap : Map.S with type key = StructName.t
module EnumName : Uid.Id with type info = Uid.MarkedString.info
module EnumConstructor : Uid.Id with type info = Uid.MarkedString.info
module EnumMap : Map.S with type key = EnumName.t

(** Abstract syntax tree for the default calculus *)

(** {1 Abstract syntax tree} *)

type typ_lit = TBool | TUnit | TInt | TRat | TMoney | TDate | TDuration

type marked_typ = typ Marked.pos

and typ =
  | TLit of typ_lit
  | TTuple of marked_typ list * StructName.t option
  | TEnum of marked_typ list * EnumName.t
  | TArrow of marked_typ * marked_typ
  | TArray of marked_typ
  | TAny

type date = Runtime.date
type duration = Runtime.duration

type lit =
  | LBool of bool
  | LEmptyError
  | LInt of Runtime.integer
  | LRat of Runtime.decimal
  | LMoney of Runtime.money
  | LUnit
  | LDate of date
  | LDuration of duration

type op_kind =
  | KInt
  | KRat
  | KMoney
  | KDate
  | KDuration  (** All ops don't have a KDate and KDuration. *)

type ternop = Fold

type binop =
  | And
  | Or
  | Xor
  | Add of op_kind
  | Sub of op_kind
  | Mult of op_kind
  | Div of op_kind
  | Lt of op_kind
  | Lte of op_kind
  | Gt of op_kind
  | Gte of op_kind
  | Eq
  | Neq
  | Map
  | Concat
  | Filter

type log_entry =
  | VarDef of typ
      (** During code generation, we need to know the type of the variable being
          logged for embedding *)
  | BeginCall
  | EndCall
  | PosRecordIfTrueBool

type unop =
  | Not
  | Minus of op_kind
  | Log of log_entry * Utils.Uid.MarkedString.info list
  | Length
  | IntToRat
  | GetDay
  | GetMonth
  | GetYear
  | RoundMoney
  | RoundDecimal

type operator = Ternop of ternop | Binop of binop | Unop of unop

(** Contains some structures used for type inference *)
module Infer : sig
  module Any : Utils.Uid.Id with type info = unit

  type unionfind_typ = typ Marked.pos UnionFind.elem
  (** We do not reuse {!type: typ} because we have to include a new [TAny]
      variant. Indeed, error terms can have any type and this has to be captured
      by the type sytem. *)

  and typ =
    | TLit of typ_lit
    | TArrow of unionfind_typ * unionfind_typ
    | TTuple of unionfind_typ list * StructName.t option
    | TEnum of unionfind_typ list * EnumName.t
    | TArray of unionfind_typ
    | TAny of Any.t

  val typ_to_ast : unionfind_typ -> marked_typ
  val ast_to_typ : marked_typ -> unionfind_typ
end

type untyped = { pos : Pos.t } [@@unboxed]
type typed = { pos : Pos.t; ty : marked_typ }
type inferring = { pos : Pos.t; uf : Infer.unionfind_typ }

(** The generic type of AST markings. Using a GADT allows functions to be
    polymorphic in the marking, but still do transformations on types when
    appropriate *)
type _ mark =
  | Untyped : untyped -> untyped mark
  | Typed : typed -> typed mark
  | Inferring : inferring -> inferring mark

type ('a, 'm) marked = ('a, 'm mark) Marked.t

type 'm marked_expr = ('m expr, 'm) marked

(** The expressions use the {{:https://lepigre.fr/ocaml-bindlib/} Bindlib}
    library, based on higher-order abstract syntax*)
and 'm expr =
  | EVar of 'm expr Bindlib.var
  | ETuple of 'm marked_expr list * StructName.t option
      (** The [MarkedString.info] is the former struct field name*)
  | ETupleAccess of 'm marked_expr * int * StructName.t option * marked_typ list
      (** The [MarkedString.info] is the former struct field name *)
  | EInj of 'm marked_expr * int * EnumName.t * marked_typ list
      (** The [MarkedString.info] is the former enum case name *)
  | EMatch of 'm marked_expr * 'm marked_expr list * EnumName.t
      (** The [MarkedString.info] is the former enum case name *)
  | EArray of 'm marked_expr list
  | ELit of lit
  | EAbs of
      (('m expr, 'm marked_expr) Bindlib.mbinder[@opaque]) * marked_typ list
  | EApp of 'm marked_expr * 'm marked_expr list
  | EAssert of 'm marked_expr
  | EOp of operator
  | EDefault of 'm marked_expr list * 'm marked_expr * 'm marked_expr
  | EIfThenElse of 'm marked_expr * 'm marked_expr * 'm marked_expr
  | ErrorOnEmpty of 'm marked_expr

(** {3 Expression annotations ([Marked.t])} *)

type typed_expr = typed marked_expr
type struct_ctx = (StructFieldName.t * marked_typ) list StructMap.t
type enum_ctx = (EnumConstructor.t * marked_typ) list EnumMap.t
type decl_ctx = { ctx_enums : enum_ctx; ctx_structs : struct_ctx }
type 'm binder = ('m expr, 'm marked_expr) Bindlib.binder

(** This kind annotation signals that the let-binding respects a structural
    invariant. These invariants concern the shape of the expression in the
    let-binding, and are documented below. *)
type scope_let_kind =
  | DestructuringInputStruct  (** [let x = input.field]*)
  | ScopeVarDefinition  (** [let x = error_on_empty e]*)
  | SubScopeVarDefinition
      (** [let s.x = fun _ -> e] or [let s.x = error_on_empty e] for input-only
          subscope variables. *)
  | CallingSubScope  (** [let result = s ({ x = s.x; y = s.x; ...}) ]*)
  | DestructuringSubScopeResults  (** [let s.x = result.x ]**)
  | Assertion  (** [let _ = assert e]*)

type ('expr, 'm) scope_let = {
  scope_let_kind : scope_let_kind;
  scope_let_typ : marked_typ;
  scope_let_expr : ('expr, 'm) marked;
  scope_let_next : ('expr, ('expr, 'm) scope_body_expr) Bindlib.binder;
  scope_let_pos : Pos.t;
}
(** This type is parametrized by the expression type so it can be reused in
    later intermediate representations. *)

(** A scope let-binding has all the information necessary to make a proper
    let-binding expression, plus an annotation for the kind of the let-binding
    that comes from the compilation of a {!module: Scopelang.Ast} statement. *)
and ('expr, 'm) scope_body_expr =
  | Result of ('expr, 'm) marked
  | ScopeLet of ('expr, 'm) scope_let

type ('expr, 'm) scope_body = {
  scope_body_input_struct : StructName.t;
  scope_body_output_struct : StructName.t;
  scope_body_expr : ('expr, ('expr, 'm) scope_body_expr) Bindlib.binder;
}
(** Instead of being a single expression, we give a little more ad-hoc structure
    to the scope body by decomposing it in an ordered list of let-bindings, and
    a result expression that uses the let-binded variables. The first binder is
    the argument of type [scope_body_input_struct]. *)

type ('expr, 'm) scope_def = {
  scope_name : ScopeName.t;
  scope_body : ('expr, 'm) scope_body;
  scope_next : ('expr, ('expr, 'm) scopes) Bindlib.binder;
}

(** Finally, we do the same transformation for the whole program for the kinded
    lets. This permit us to use bindlib variables for scopes names. *)
and ('expr, 'm) scopes = Nil | ScopeDef of ('expr, 'm) scope_def

type 'm program = { decl_ctx : decl_ctx; scopes : ('m expr, 'm) scopes }

(** {1 Helpers} *)

(** {2 Manipulation of marks} *)

val no_mark : 'm mark -> 'm mark
val mark_pos : 'm mark -> Pos.t
val pos : ('a, 'm) marked -> Pos.t
val ty : ('a, typed) marked -> marked_typ
val with_ty : marked_typ -> ('a, 'm) marked -> ('a, typed) marked

(** All the following functions will resolve the types if called on an
    [Inferring] type *)

val map_mark :
  (Pos.t -> Pos.t) -> (marked_typ -> marked_typ) -> 'm mark -> 'm mark

val map_mark2 :
  (Pos.t -> Pos.t -> Pos.t) ->
  (typed -> typed -> marked_typ) ->
  'm mark ->
  'm mark ->
  'm mark

val fold_marks :
  (Pos.t list -> Pos.t) -> (typed list -> marked_typ) -> 'm mark list -> 'm mark

val get_scope_body_mark : ('expr, 'm) scope_body -> 'm mark
val untype_expr : 'm marked_expr -> untyped marked_expr
val untype_program : 'm program -> untyped program

(** {2 Boxed constructors} *)

val evar : 'm expr Bindlib.var -> 'm mark -> 'm marked_expr Bindlib.box

val etuple :
  'm marked_expr Bindlib.box list ->
  StructName.t option ->
  'm mark ->
  'm marked_expr Bindlib.box

val etupleaccess :
  'm marked_expr Bindlib.box ->
  int ->
  StructName.t option ->
  marked_typ list ->
  'm mark ->
  'm marked_expr Bindlib.box

val einj :
  'm marked_expr Bindlib.box ->
  int ->
  EnumName.t ->
  marked_typ list ->
  'm mark ->
  'm marked_expr Bindlib.box

val ematch :
  'm marked_expr Bindlib.box ->
  'm marked_expr Bindlib.box list ->
  EnumName.t ->
  'm mark ->
  'm marked_expr Bindlib.box

val earray :
  'm marked_expr Bindlib.box list -> 'm mark -> 'm marked_expr Bindlib.box

val elit : lit -> 'm mark -> 'm marked_expr Bindlib.box

val eabs :
  ('m expr, 'm marked_expr) Bindlib.mbinder Bindlib.box ->
  marked_typ list ->
  'm mark ->
  'm marked_expr Bindlib.box

val eapp :
  'm marked_expr Bindlib.box ->
  'm marked_expr Bindlib.box list ->
  'm mark ->
  'm marked_expr Bindlib.box

val eassert :
  'm marked_expr Bindlib.box -> 'm mark -> 'm marked_expr Bindlib.box

val eop : operator -> 'm mark -> 'm marked_expr Bindlib.box

val edefault :
  'm marked_expr Bindlib.box list ->
  'm marked_expr Bindlib.box ->
  'm marked_expr Bindlib.box ->
  'm mark ->
  'm marked_expr Bindlib.box

val eifthenelse :
  'm marked_expr Bindlib.box ->
  'm marked_expr Bindlib.box ->
  'm marked_expr Bindlib.box ->
  'm mark ->
  'm marked_expr Bindlib.box

val eerroronempty :
  'm marked_expr Bindlib.box -> 'm mark -> 'm marked_expr Bindlib.box

type ('expr, 'm) box_expr_sig =
  ('expr, 'm) marked -> ('expr, 'm) marked Bindlib.box

val box_expr : ('m expr, 'm) box_expr_sig

(**{2 Program traversal}*)

(** Be careful when using these traversal functions, as the bound variables they
    open will be different at each traversal. *)

val map_expr :
  'a ->
  f:('a -> 'm1 marked_expr -> 'm2 marked_expr Bindlib.box) ->
  ('m1 expr, 'm2 mark) Marked.t ->
  'm2 marked_expr Bindlib.box
(** If you want to apply a map transform to an expression, you can save up
    writing a painful match over all the cases of the AST. For instance, if you
    want to remove all errors on empty, you can write

    {[
      let remove_error_empty =
        let rec f () e =
          match Marked.unmark e with
          | ErrorOnEmpty e1 -> map_expr () f e1
          | _ -> map_expr () f e
        in
        f () e
    ]}

    The first argument of map_expr is an optional context that you can carry
    around during your map traversal. *)

val map_expr_top_down :
  f:('m1 marked_expr -> ('m1 expr, 'm2 mark) Marked.t) ->
  'm1 marked_expr ->
  'm2 marked_expr Bindlib.box
(** Recursively applies [f] to the nodes of the expression tree. The type
    returned by [f] is hybrid since the mark at top-level has been rewritten,
    but not yet the marks in the subtrees. *)

val map_expr_marks :
  f:('m1 mark -> 'm2 mark) -> 'm1 marked_expr -> 'm2 marked_expr

val fold_left_scope_lets :
  f:('a -> ('expr, 'm) scope_let -> 'expr Bindlib.var -> 'a) ->
  init:'a ->
  ('expr, 'm) scope_body_expr ->
  'a
(** Usage:
    [fold_left_scope_lets ~f:(fun acc scope_let scope_let_var -> ...) ~init scope_lets],
    where [scope_let_var] is the variable bound to the scope let in the next
    scope lets to be examined. *)

val fold_right_scope_lets :
  f:(('expr1, 'm1) scope_let -> 'expr1 Bindlib.var -> 'a -> 'a) ->
  init:(('expr1, 'm1) marked -> 'a) ->
  ('expr1, 'm1) scope_body_expr ->
  'a
(** Usage:
    [fold_right_scope_lets ~f:(fun scope_let scope_let_var acc -> ...) ~init scope_lets],
    where [scope_let_var] is the variable bound to the scope let in the next
    scope lets to be examined (which are before in the program order). *)

val map_exprs_in_scope_lets :
  f:(('expr1, 'm1) marked -> ('expr2, 'm2) marked Bindlib.box) ->
  varf:('expr1 Bindlib.var -> 'expr2 Bindlib.var) ->
  ('expr1, 'm1) scope_body_expr ->
  ('expr2, 'm2) scope_body_expr Bindlib.box

val fold_left_scope_defs :
  f:('a -> ('expr1, 'm1) scope_def -> 'expr1 Bindlib.var -> 'a) ->
  init:'a ->
  ('expr1, 'm1) scopes ->
  'a
(** Usage:
    [fold_left_scope_defs ~f:(fun acc scope_def scope_var -> ...) ~init scope_def],
    where [scope_var] is the variable bound to the scope in the next scopes to
    be examined. *)

val fold_right_scope_defs :
  f:(('expr1, 'm1) scope_def -> 'expr1 Bindlib.var -> 'a -> 'a) ->
  init:'a ->
  ('expr1, 'm1) scopes ->
  'a
(** Usage:
    [fold_right_scope_defs ~f:(fun  scope_def scope_var acc -> ...) ~init scope_def],
    where [scope_var] is the variable bound to the scope in the next scopes to
    be examined (which are before in the program order). *)

val map_scope_defs :
  f:(('expr, 'm) scope_def -> ('expr, 'm) scope_def Bindlib.box) ->
  ('expr, 'm) scopes ->
  ('expr, 'm) scopes Bindlib.box

val map_exprs_in_scopes :
  f:(('expr1, 'm1) marked -> ('expr2, 'm2) marked Bindlib.box) ->
  varf:('expr1 Bindlib.var -> 'expr2 Bindlib.var) ->
  ('expr1, 'm1) scopes ->
  ('expr2, 'm2) scopes Bindlib.box
(** This is the main map visitor for all the expressions inside all the scopes
    of the program. *)

(** {2 Variables} *)

type 'm var = 'm expr Bindlib.var

val new_var : string -> 'm var

val translate_var : 'm1 var -> 'm2 var
(** used to convert between e.g. [untyped expr var] into a [typed expr var] *)

module Var : sig
  type t

  val t : 'm expr Bindlib.var -> t
  (** Hides the marking type parameter annotation behind an existential type so
      that variables can be stored in non-polymorphic sets and maps *)

  val get : t -> 'm expr Bindlib.var
  (** Be careful with this, it breaks the type abstraction by casting the
      existential type annotation. See [!Bindlib.copy_var] for more detail. *)

  val compare : t -> t -> int
  val eq : t -> t -> bool
end

module VarMap : Map.S with type key = Var.t
module VarSet : Set.S with type elt = Var.t

val free_vars_expr : 'm marked_expr -> VarSet.t
val free_vars_scope_body_expr : ('m expr, 'm) scope_body_expr -> VarSet.t
val free_vars_scope_body : ('m expr, 'm) scope_body -> VarSet.t
val free_vars_scopes : ('m expr, 'm) scopes -> VarSet.t

(* type vars = expr Bindlib.mvar *)

val make_var : ('m var, 'm) marked -> 'm marked_expr Bindlib.box

(** {2 Boxed term constructors} *)

type ('e, 'm) make_abs_sig =
  'e Bindlib.mvar ->
  ('e, 'm) marked Bindlib.box ->
  marked_typ list ->
  'm mark ->
  ('e, 'm) marked Bindlib.box

val make_abs : ('m expr, 'm) make_abs_sig

val make_app :
  'm marked_expr Bindlib.box ->
  'm marked_expr Bindlib.box list ->
  'm mark ->
  'm marked_expr Bindlib.box

type ('expr, 'm) make_let_in_sig =
  'expr Bindlib.var ->
  marked_typ ->
  ('expr, 'm) marked Bindlib.box ->
  ('expr, 'm) marked Bindlib.box ->
  Pos.t ->
  ('expr, 'm) marked Bindlib.box

val make_let_in : ('m expr, 'm) make_let_in_sig

(**{2 Other}*)

val empty_thunked_term : 'm mark -> 'm marked_expr
val is_value : 'm marked_expr -> bool

val equal_exprs : 'm marked_expr -> 'm marked_expr -> bool
(** Determines if two expressions are equal, omitting their position information *)

(** {1 AST manipulation helpers}*)

val build_whole_scope_expr :
  box_expr:('expr, 'm) box_expr_sig ->
  make_abs:('expr, 'm) make_abs_sig ->
  make_let_in:('expr, 'm) make_let_in_sig ->
  decl_ctx ->
  ('expr, 'm) scope_body ->
  'm mark ->
  ('expr, 'm) marked Bindlib.box
(** Usage: [build_whole_scope_expr ctx body scope_position] where
    [scope_position] corresponds to the line of the scope declaration for
    instance. *)

type 'expr scope_name_or_var =
  | ScopeName of ScopeName.t
  | ScopeVar of 'expr Bindlib.var

val unfold_scopes :
  box_expr:('expr, 'm) box_expr_sig ->
  make_abs:('expr, 'm) make_abs_sig ->
  make_let_in:('expr, 'm) make_let_in_sig ->
  decl_ctx ->
  ('expr, 'm) scopes ->
  'm mark ->
  'expr scope_name_or_var ->
  ('expr, 'm) marked Bindlib.box

val build_whole_program_expr :
  'm program -> ScopeName.t -> 'm marked_expr Bindlib.box
(** Usage: [build_whole_program_expr program main_scope] builds an expression
    corresponding to the main program and returning the main scope as a
    function. *)

val expr_size : 'm marked_expr -> int
(** Used by the optimizer to know when to stop *)

val remove_logging_calls : 'm marked_expr -> 'm marked_expr Bindlib.box
(** Removes all calls to [Log] unary operators in the AST, replacing them by
    their argument. *)

val build_scope_typ_from_sig :
  decl_ctx -> StructName.t -> StructName.t -> Pos.t -> typ Marked.pos
(** [build_scope_typ_from_sig ctx in_struct out_struct pos] builds the arrow
    type for the specified scope *)