A type of deriving plugins.

A structure or signature deriving function accepts a list of ~options, a ~path of modules for the type declaration currently being processed (with [] for toplevel phrases), and a type declaration item (type t = .. and t' = ..), and returns a list of items to be appended after the type declaration item in structure and signature. It is invoked by [\@\@deriving] annotations.

A type deriving function accepts a type and returns a corresponding derived expression. It is invoked by [%derive.foo:] and [%foo:] annotations. If this function is missing, the corresponding [%foo:] annotation is ignored.

The structure and signature deriving functions are invoked in the order in which they appear in the source code.

register deriver registers deriver according to its name field.

add_register_hook hook adds hook to be executed whenever a new deriver is registered.

derivers () returns all currently registered derivers.

Creating deriver structure.

lookup name looks up a deriver called name.

Error handling

string_of_core_type typ unparses typ, omitting any attributes.

string_of_constant_opt c returns Some s if the constant c is a string s, None otherwise.

string_of_expression_opt e returns Some s if the expression e is a string constant s, None otherwise.

Arg contains convenience functions that extract constants from AST fragments, to be used when parsing options or [\@attributes] attached to types, fields or constructors.

A quoter remembers a set of expressions.

quoter () creates an empty quoter.

quote quoter expr records a pure expression expr within quoter and returns an expression which has the same value as expr in the context that sanitize provides.

sanitize module_ quoter expr wraps expr in a way that ensures that the contents of module_ and Stdlib, as well as the identifiers in expressions returned by quote are in scope, and returns the wrapped expression. module_ defaults to Ppx_deriving_runtime if it's not provided

with_quoter fn ≡ fun fn a -> let quoter = create_quoter () in sanitize ~quoter (fn quoter a)

expand_path name returns name with the path module path prepended, e.g. expand_path ["Foo";"M"] "t" = "Foo.M.t" and expand_path [] "t" = "t"

path_of_type_decl ~path type_ returns path if type_ does not have a manifest or the manifest is not a constructor, and the module path of manifest otherwise.

path_of_type_decl is useful when determining the canonical path location of fields and constructors; e.g. for type bar = M.foo = A | B, it will return ["M"].

mangle_type_decl ~fixpoint affix type_ derives a function name from type_ name by doing nothing if type_ is named fixpoint ("t" by default), or appending and/or prepending affix via an underscore.

mangle_lid ~fixpoint affix lid does the same as mangle_type_decl, but for the last component of lid.

attr ~deriver name attrs searches for an attribute [\@deriving.deriver.attr] in attrs if any attribute with name starting with \@deriving.deriver exists, or [\@deriver.attr] if any attribute with name starting with \@deriver exists, or [\@attr] otherwise.

attr_warning expr builds the attribute \@ocaml.warning expr

free_vars_in_core_type typ returns unique free variables in typ in lexical order.

remove_pervasives ~deriver typ removes the leading "Pervasives." and "Stdlib." module name in longidents. Type expressions marked with [\@nobuiltin] are ignored.

The name of the deriving plugin should be passed as deriver; it is used in error messages.

fresh_var bound returns a fresh variable name not present in bound. The name is selected in alphabetical succession.

fold_left_type_decl fn accum type_ performs a left fold over all type variable (i.e. not wildcard) parameters in type_.

fold_right_type_decl fn accum type_ performs a right fold over all type variable (i.e. not wildcard) parameters in type_.

fold_left_type_ext fn accum type_ performs a left fold over all type variable (i.e. not wildcard) parameters in type_.

fold_right_type_ext fn accum type_ performs a right fold over all type variable (i.e. not wildcard) parameters in type_.

poly_fun_of_type_decl type_ expr wraps expr into fun poly_N -> ... for every type parameter 'N present in type_. For example, if type_ refers to type ('a, 'b) map, expr will be wrapped into fun poly_a poly_b -> [%e expr].

_ parameters are ignored.

Same as poly_fun_of_type_decl but for type extension.

poly_apply_of_type_decl type_ expr wraps expr into expr poly_N for every type parameter 'N present in type_. For example, if type_ refers to type ('a, 'b) map, expr will be wrapped into [%e expr] poly_a poly_b.

_ parameters are ignored.

Same as poly_apply_of_type_decl but for type extension.

poly_arrow_of_type_decl fn type_ typ wraps typ in an arrow with fn [%type: 'N] as argument for every type parameter 'N present in type_. For example, if type_ refers to type ('a, 'b) map and fn is fun var -> [%type: [%t var] -> string], typ will be wrapped into ('a -> string) -> ('b -> string) -> [%t typ].

_ parameters are ignored.

Same as poly_arrow_of_type_decl but for type extension.

core_type_of_type_decl type_ constructs type ('a, 'b, ...) t for type declaration type ('a, 'b, ...) t = ....

Same as core_type_of_type_decl but for type extension.

instantiate bound type_ returns typ, vars, bound' where typ is a type instantiated from type declaration type_, vars ≡ free_vars_in_core_type typ and bound' ≡ bound @ vars.

fold_exprs ~unit fn exprs folds exprs using head of exprs as initial accumulator value, or unit if exprs = [].

See also seq_reduce and binop_reduce.

When sep is present: seq_reduce ≡ fun x a b -> [%expr [%e a]; [%e x]; [%e b]]. When sep is missing: seq_reduce ≡ fun a b -> [%expr [%e a]; [%e b]].

binop_reduce ≡ fun x a b -> [%expr [%e x] [%e a] [%e b]].

strong_type_of_type ty transform a type ty to freevars . ty, giving a strong polymorphic type

hash_variant x ≡ Btype.hash_variant x.