Module Drom_toml.Lenses

Partial lenses (returns option) for accessing TOML structures. They make it possible to read/write deeply nested immutable values.

type ('a, 'b) lens = {
  1. get : 'a -> 'b option;
  2. set : 'b -> 'a -> 'a option;
}
val get : 'a -> ('a, 'b) lens -> 'b option

Extracts a value from some Toml data using a lens. Returns Some value if the underlying data matched the lens, or None.

Example:

  utop # let toml_data = Toml.Parser.(from_string "
  [this.is.a.deeply.nested.table]
  answer=42" |> unsafe);;
  val toml_data : Types.table = <abstr>

  utop # Toml.Lenses.(get toml_data (
    key "this" |-- table
    |-- key "is" |-- table
    |-- key "a" |-- table
    |-- key "deeply" |-- table
    |-- key "nested" |-- table
    |-- key "table" |-- table
    |-- key "answer"|-- int ));;
  - : int option = Some 42
  • since 4.0.0
val set : 'b -> 'a -> ('a, 'b) lens -> 'a option

Replaces an existing value in some Toml data using a lens. Returns Some value if the underlying data matched the lens, or None.

Example:

  utop # let toml_data = Toml.Parser.(from_string "
  [this.is.a.deeply.nested.table]
  answer=42" |> unsafe);;
  val toml_data : Types.table = <abstr>

  utop # let maybe_toml_data' = Toml.Lenses.(set 2015 toml_data (
    key "this" |-- table
    |-- key "is" |-- table
    |-- key "a" |-- table
    |-- key "deeply" |-- table
    |-- key "nested" |-- table
    |-- key "table" |-- table
    |-- key "answer"|-- int ));;
  val maybe_toml_data' : Types.table option = Some <abstr>

  utop # let (Some toml_data') = maybe_toml_data';;
  val toml_data' : Types.table = <abstr>

  utop # Toml.Printer.string_of_table toml_data';;
  - : bytes = "[this.is.a.deeply.nested.table]\nanswer = 2015\n"
  • since 4.0.0
val update : ('b -> 'b option) -> 'a -> ('a, 'b) lens -> 'a option

Applies a function on an existing value in some Toml data. Returns Some value if the underlying data matched the lens, or None.

Example:

  utop # let toml_data = Toml.Parser.(from_string "
    [[table.of.mixed_values]]
    int=0
    str=\"a\"
    [[table.of.mixed_values]]
    str=\"b\"
    [[table.of.mixed_values]]
    int=3
  " |> unsafe);;
  val toml_data : Types.table = <abstr>

  utop # let maybe_toml_data' =  Toml.Lenses.(update
    (fun ts -> Some (
      List.map (fun t ->
        (** Add 'int=42' to each table which doesn't already have an 'int' key *)
        if not (Types.Table.mem (Toml.key "int") t) then
          Types.Table.add (Toml.key "int") (Types.TInt 42) t
        else t) ts))
    toml_data
    (key "table" |-- table
     |-- key "of" |-- table
     |-- key "mixed_values" |-- array |-- tables));;
  val maybe_toml_data' : Types.table option = Some <abstr>

  utop # let (Some toml_data') = maybe_toml_data';;
  val toml_data' : Types.table = <abstr>

  utop # print_endline @@ Toml.Printer.string_of_table toml_data';;

  [[table.of.mixed_values]]
  int = 0
  str = "a"
  [[table.of.mixed_values]]
  int = 42
  str = "b"
  [[table.of.mixed_values]]
  int = 3
  - : unit = ()
  • since 4.0.0
val compose : ('a, 'b) lens -> ('c, 'a) lens -> ('c, 'b) lens

Lens composition.

  • since 4.0.0
val (|--) : ('a, 'b) lens -> ('b, 'c) lens -> ('a, 'c) lens

Flipped lens composition.

  • since 4.0.0
val key : string -> (Types.table, Types.value) lens

Lens to a particular value in a table.

  • raises Types.Table.Key.Bad_key

    if the key contains invalid characters.

  • since 4.0.0
val field : string -> (Types.table, Types.table) lens

Combines the key and table lenses, for the common case of nested tables.

  • raises Types.Table.Key.Bad_key

    if the key contains invalid characters.

  • since 4.0.0
val string : (Types.value, string) lens

Lens to a string value.

  • since 4.0.0
val bool : (Types.value, bool) lens

Lens to a boolean value.

  • since 4.0.0
val int : (Types.value, int) lens

Lens to an int value.

  • since 4.0.0
val float : (Types.value, float) lens

Lens to a float value.

  • since 4.0.0
val date : (Types.value, float) lens

Lens to a date value.

  • since 4.0.0

Lens to an array value.

  • since 4.0.0

Lens to a table value.

  • since 4.0.0
val strings : (Types.array, string list) lens

Lens to an array of strings.

  • since 4.0.0
val bools : (Types.array, bool list) lens

Lens to an array of booleans.

  • since 4.0.0
val ints : (Types.array, int list) lens

Lens to an array of ints.

  • since 4.0.0
val floats : (Types.array, float list) lens

Lens to an array of floats.

  • since 4.0.0
val dates : (Types.array, float list) lens

Lens to an array of dates.

  • since 4.0.0
val tables : (Types.array, Types.table list) lens

Lens to an array of tables.

  • since 4.0.0
val arrays : (Types.array, Types.array list) lens

Lens to an array of arrays.

  • since 4.0.0