This module is similar to the Ast_helper module distributed with OCaml but uses different conventions.

Locations

Ast_helper uses a global variable for the default locations, we found that to it makes it quite easy to mess up locations. Instead this modules forces you to provide a location argument.

For building fragment using the same location everywhere, a functor is provided.

Naming

The names match the Parsetree names closely, which makes it easy to build AST fragments by just knowing the Parsetree.

For types of the form a wrapper record with a _desc field, helpers are generated for each constructor constructing the record directly. For instance for the type Parsetree.expression:

type expression =
  { pexp_desc       : expression_desc
  ; pexp_loc        : Location.t
  ; pexp_attributes : attributes
  }

and expression_desc =
  | Pexp_ident    of Longident.t loc
  | Pexp_constant of constant
  | Pexp_let      of rec_flag * value_binding list * expression
  ...

The following helpers are created:

val pexp_ident    : loc:Location.t -> Longident.t Located.t          -> expression
val pexp_constant : loc:Location.t -> constant                       -> expression
val pexp_let      : loc:Location.t -> rec_flag -> value_binding list -> expression
...

For other record types, such as type_declaration, we have the following helper:

type type_declaration =
  { ptype_name       : string Located.t
  ; ptype_params     : (core_type * variance) list
  ; ptype_cstrs      : (core_type * core_type * Location.t) list
  ; ptype_kind       : type_kind
  ; ptype_private    : private_flag
  ; ptype_manifest   : core_type option
  ; ptype_attributes : attributes
  ; ptype_loc        : Location.t
  }


val type_declaration
  :  loc      : Location.t
  -> name     : string Located.t
  -> params   : (core_type * variance) list
  -> cstrs    : (core_type * core_type * Location.t) list
  -> kind     : type_kind
  -> private  : private_flag
  -> manifest : core_type option
  -> type_declaration

Attributes are always set to the empty list. If you want to set them you have to override the field with the { e with pexp_attributes = ... } notation.