Module 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 = {
get : 'a -> 'b option;
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
val array : ( Types.value, Types.array ) lens

Lens to an array value.

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

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