package ocaml-base-compiler

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package ocaml-base-compiler
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Representation of types and declarations

Types defines the representation of types and declarations (that is, the content of module signatures).

CMI files are made of marshalled types.

Asttypes exposes basic definitions shared both by Parsetree and Types.

type type_expr

Type expressions for the core language.

The type_desc variant defines all the possible type expressions one can find in OCaml. type_expr wraps this with some annotations.

The level field tracks the level of polymorphism associated to a type, guiding the generalization algorithm. Put shortly, when referring to a type in a given environment, both the type and the environment have a level. If the type has an higher level, then it can be considered fully polymorphic (type variables will be printed as 'a), otherwise it'll be weakly polymorphic, or non generalized (type variables printed as '_a). See http://okmij.org/ftp/ML/generalization.html for more information.

Note about type_declaration: one should not make the confusion between type_expr and type_declaration.

type_declaration refers specifically to the type construct in OCaml language, where you create and name a new type or type alias.

type_expr is used when you refer to existing types, e.g. when annotating the expected type of a value.

Also, as the type system of OCaml is generative, a type_declaration can have the side-effect of introducing a new type constructor, different from all other known types. Whereas type_expr is a pure construct which allows referring to existing types.

Note on mutability: TBD.

type row_desc
type row_field
type field_kind
type commutable
type type_desc =
  1. | Tvar of string option
    (*

    Tvar (Some "a") ==> 'a or '_a Tvar None ==> _

    *)
  2. | Tarrow of Asttypes.arg_label * type_expr * type_expr * commutable
    (*

    Tarrow (Nolabel, e1, e2, c) ==> e1 -> e2 Tarrow (Labelled "l", e1, e2, c) ==> l:e1 -> e2 Tarrow (Optional "l", e1, e2, c) ==> ?l:e1 -> e2

    See commutable for the last argument.

    *)
  3. | Ttuple of type_expr list
    (*

    Ttuple [t1;...;tn] ==> (t1 * ... * tn)

    *)
  4. | Tconstr of Path.t * type_expr list * abbrev_memo ref
    (*

    Tconstr (`A.B.t', [t1;...;tn], _) ==> (t1,...,tn) A.B.t The last parameter keep tracks of known expansions, see abbrev_memo.

    *)
  5. | Tobject of type_expr * (Path.t * type_expr list) option ref
    (*

    Tobject (`f1:t1;...;fn: tn', `None') ==> < f1: t1; ...; fn: tn > f1, fn are represented as a linked list of types using Tfield and Tnil constructors.

    Tobject (_, `Some (`A.ct', [t1;...;tn]') ==> (t1, ..., tn) A.ct. where A.ct is the type of some class.

    There are also special cases for so-called "class-types", cf. Typeclass and Ctype.set_object_name:

    Tobject (Tfield(_,_,...(Tfield(_,_,rv)...), Some(`A.#ct`, [rv;t1;...;tn]) ==> (t1, ..., tn) #A.ct Tobject (_, Some(`A.#ct`, [Tnil;t1;...;tn]) ==> (t1, ..., tn) A.ct

    where rv is the hidden row variable.

    *)
  6. | Tfield of string * field_kind * type_expr * type_expr
    (*

    Tfield ("foo", field_public, t, ts) ==> <...; foo : t; ts>

    *)
  7. | Tnil
    (*

    Tnil ==> <...; >

    *)
  8. | Tsubst of type_expr * type_expr option
    (*

    Tsubst is used temporarily to store information in low-level functions manipulating representation of types, such as instantiation or copy. The first argument contains a copy of the original node. The second is available only when the first is the row variable of a polymorphic variant. It then contains a copy of the whole variant. This constructor should not appear outside of these cases.

    *)
  9. | Tvariant of row_desc
    (*

    Representation of polymorphic variants, see row_desc.

    *)
  10. | Tunivar of string option
    (*

    Occurrence of a type variable introduced by a forall quantifier / Tpoly.

    *)
  11. | Tpoly of type_expr * type_expr list
    (*

    Tpoly (ty,tyl) ==> 'a1... 'an. ty, where 'a1 ... 'an are names given to types in tyl and occurrences of those types in ty.

    *)
  12. | Tpackage of Path.t * (Longident.t * type_expr) list
    (*

    Type of a first-class module (a.k.a package).

    *)
and fixed_explanation =
  1. | Univar of type_expr
    (*

    The row type was bound to an univar

    *)
  2. | Fixed_private
    (*

    The row type is private

    *)
  3. | Reified of Path.t
    (*

    The row was reified

    *)
  4. | Rigid
    (*

    The row type was made rigid during constraint verification

    *)
and abbrev_memo =
  1. | Mnil
    (*

    No known abbreviation

    *)
  2. | Mcons of Asttypes.private_flag * Path.t * type_expr * type_expr * abbrev_memo
    (*

    Found one abbreviation. A valid abbreviation should be at least as visible and reachable by the same path. The first expression is the abbreviation and the second the expansion.

    *)

abbrev_memo allows one to keep track of different expansions of a type alias. This is done for performance purposes.

For instance, when defining type 'a pair = 'a * 'a, when one refers to an 'a pair, it is just a shortcut for the 'a * 'a type. This expansion will be stored in the abbrev_memo of the corresponding Tconstr node.

In practice, abbrev_memo behaves like list of expansions with a mutable tail.

Note on marshalling: abbrev_memo must not appear in saved types. Btype, with cleanup_abbrev and memo, takes care of tracking and removing abbreviations.

commutable is a flag appended to every arrow type.

When typing an application, if the type of the functional is known, its type is instantiated with commu_ok arrows, otherwise as commu_var ().

When the type is not known, the application will be used to infer the actual type. This is fragile in presence of labels where there is no principal type.

Two incompatible applications must rely on is_commu_ok arrows, otherwise they will trigger an error.

let f g = g ~a:() ~b:(); g ~b:() ~a:();

Error: This function is applied to arguments in an order different from other calls. This is only allowed when the real type is known.

val is_commu_ok : commutable -> bool
val commu_ok : commutable
val commu_var : unit -> commutable

field_kind indicates the accessibility of a method.

An Fprivate field may become Fpublic or Fabsent during unification, but not the other way round.

The same field_kind is kept shared when copying Tfield nodes so that the copies of the self-type of a class share the same accessibility (see also PR#10539).

type field_kind_view =
  1. | Fprivate
  2. | Fpublic
  3. | Fabsent
val field_kind_repr : field_kind -> field_kind_view
val field_public : field_kind
val field_absent : field_kind
val field_private : unit -> field_kind
val field_kind_internal_repr : field_kind -> field_kind

Getters for type_expr; calls repr before answering a value

val get_desc : type_expr -> type_desc
val get_level : type_expr -> int
val get_scope : type_expr -> int
val get_id : type_expr -> int
type transient_expr = private {
  1. mutable desc : type_desc;
  2. mutable level : int;
  3. mutable scope : int;
  4. id : int;
}

Transient type_expr. Should only be used immediately after Transient_expr.repr

module Transient_expr : sig ... end

Operations on transient_expr

val create_expr : type_desc -> level:int -> scope:int -> id:int -> type_expr

Functions and definitions moved from Btype

val newty3 : level:int -> scope:int -> type_desc -> type_expr

Create a type with a fresh id

val newty2 : level:int -> type_desc -> type_expr

Create a type with a fresh id and no scope

module TransientTypeOps : sig ... end

Comparisons for functors

Comparisons for type_expr; cannot be used for functors

val eq_type : type_expr -> type_expr -> bool
val compare_type : type_expr -> type_expr -> int

Constructor and accessors for row_desc

`X | `Y (row_closed = true) < `X | `Y (row_closed = true) > `X | `Y (row_closed = false) < `X | `Y > `X (row_closed = true)

type t = > `X as 'a (row_more = Tvar a) type t = private > `X (row_more = Tconstr ("t#row", , ref Mnil))

And for:

let f = function `X -> `X -> | `Y -> `X

the type of "f" will be a Tarrow whose lhs will (basically) be:

Tvariant row_fields = [("X", _)]; row_more = Tvariant { row_fields = [("Y", _)]; row_more = Tvariant { row_fields = []; row_more = _; _ ; _

}

; _

}

val create_row : fields:(Asttypes.label * row_field) list -> more:type_expr -> closed:bool -> fixed:fixed_explanation option -> name:(Path.t * type_expr list) option -> row_desc
val row_fields : row_desc -> (Asttypes.label * row_field) list
val row_more : row_desc -> type_expr
val row_closed : row_desc -> bool
val row_fixed : row_desc -> fixed_explanation option
val row_name : row_desc -> (Path.t * type_expr list) option
val set_row_name : row_desc -> (Path.t * type_expr list) option -> row_desc
val get_row_field : Asttypes.label -> row_desc -> row_field
type row_desc_repr =
  1. | Row of {
    1. fields : (Asttypes.label * row_field) list;
    2. more : type_expr;
    3. closed : bool;
    4. fixed : fixed_explanation option;
    5. name : (Path.t * type_expr list) option;
    }

get all fields at once; different from the old row_repr

val row_repr : row_desc -> row_desc_repr
type row_field_view =
  1. | Rpresent of type_expr option
  2. | Reither of bool * type_expr list * bool
  3. | Rabsent

Current contents of a row field

val row_field_repr : row_field -> row_field_view
val rf_present : type_expr option -> row_field
val rf_absent : row_field
val rf_either : ?use_ext_of:row_field -> no_arg:bool -> type_expr list -> matched:bool -> row_field
val rf_either_of : type_expr option -> row_field
val eq_row_field_ext : row_field -> row_field -> bool
val changed_row_field_exts : row_field list -> (unit -> unit) -> bool
val match_row_field : present:(type_expr option -> 'a) -> absent:(unit -> 'a) ->