package ppx_yojson

ppx_yojson

PPX extension for Yojson literals and patterns

Overview

ppx_yojson lets you write Yojson expressions and patterns using ocaml syntax to make your code more concise and readable.

For example you can turn:

let json =
  `List
    [ `Assoc
        [ ("name", `String "Anne")
        ; ("grades", `List [`String "A"; `String "B-"; `String "B+"]
        ]
    ; `Assoc
        [ ("name", `String "Bernard")
        ; ("grades", `List [`String "B+"; `String "A"; `String "B-"]
        ]
    ]

into:

let json =
  [%yojson
    [ {name = "Anne"; grades = ["A"; "B-"; "B+"]}
    ; {name = "Anne"; grades = ["A"; "B-"; "B+"]}
    ]
  ]

Expressions

The expression rewriter supports the following Yojson values:

• Null: [%yojson None]
• Bool of bool: [%yojson true]
• Float of float: [%yojson 1.2e+10]
• Int of int: [%yojson 0xff]. As long as the int literal in the payload fits in an int, the 0x, 0o and 0b notations are accepted.
• Intlit of string: [%yojson 100000000000000000000000000000000]. For arbitrary long integers, 0x, 0o and 0b notations are currently not supported and the rewriter will raise an error.
• String of string: [%yojson "abc"]
• List of json list: [%yojson [1; 2; 3]]. It supports mixed type list as well such as ["a"; 2].
• Assoc of (string * json) list: [%yojson {a = 1; b = "b"}]
• any valid combination of the above

The resulting expression are not constrained, meaning it works with Yojson.Safe or Yojson.Basic regardless.

Patterns

Currently unsupported, coming soon.