Add few functions to the utils module

CHANGES.md

@@ -20,6 +20,8 @@
 
 - Add an opam package `yojson-bench` to deal with benchmarks dependency
   (@tmcgilchrist, #117)
+- Added utilitaries function `assoc_map`, `assoc_map_filter`, `add`, `update`
+  and `remove` to the `Utils` module (@panglesd, #127)
 
 ### Change
 

lib/util.ml

@@ -202,3 +202,49 @@ let combine (first : t) (second : t) =
   match (first, second) with
   | (`Assoc a, `Assoc b) -> (`Assoc (a @ b) :  t)
   | (a, b) -> raise (Invalid_argument "Expected two objects, check inputs")
+
+let assoc_map f json = match json with
+  | `Assoc l -> 
+    let rec map res l = match l with
+        [] -> res
+      | (k,v) :: q -> map ( (k,f (k,v)) :: res) q in
+    `Assoc (List.rev @@ map [] l)
+  | js -> typerr "Can't assoc_map over non-object type " js
+
+let assoc_map_filter f json = match json with
+  | `Assoc l -> 
+    let rec map res l = match l with
+        [] -> res
+      | (k,v) :: q ->
+        match f (k,v) with
+          None -> map (res) q
+        | Some v -> map ( (k,v) :: res) q in
+    `Assoc (List.rev @@ map [] l)
+  | js -> typerr "Can't assoc_map_filter over non-object type " js
+
+let add json pair = match json with
+  | `Assoc l -> `Assoc (pair :: l)
+  | js -> typerr "Can't assoc_map_filter over non-object type " js
+
+let update json (key, value) = match json with
+  | `Assoc l ->
+    let rec map res l = match l with
+        [] -> List.rev res
+      | (k,v) :: q when k = key ->
+        List.rev_append res ((k, value) :: q)
+      | a :: q ->
+        map (a::res) q in
+    `Assoc (map [] l)
+  | js -> typerr "Can't update field of non-object type " js
+
+let remove json key = match json with
+  | `Assoc l ->
+    let rec map res l = match l with
+        [] -> List.rev res
+      | (k,v) :: q when k = key ->
+        List.rev_append res q
+      | a :: q ->
+        map (a::res) q in
+    `Assoc (map [] l)
+  | js -> typerr "Can't remove field on non-object type " js
+

lib/util.mli

@@ -74,6 +74,17 @@ val keys : t -> string list
 val values : t -> t list
   (** Return all the value in the given JSON object *)
 
+val add : t -> (string * t) -> t
+  (** Add an entry to a JSON object *)
+
+val update : t -> (string * t) -> t
+  (** [update json (key, value)] updates the first field with key [key] of the
+      JSON object [json] to [value] *)
+
+val remove : t -> string -> t
+  (** [remove json key] remove the first field with key [key] of the
+      JSON object [json] *)
+
 val combine : t -> t -> t
   (** Combine two JSON Objects together *)
 
@@ -90,6 +101,15 @@ val map : (t -> t) -> t -> t
   (** [map f arr] calls the function [f] on each element of the JSON array
       [arr], and returns a JSON array containing the results. *)
 
+val assoc_map : (string  * t -> t) -> t -> t
+  (** [assoc_map f json] calls the function [f] on each [(key, value)] pair of
+      the JSON object [json], and returns a JSON object containing the updated
+      [(key, f (key, value))]. *)
+
+val assoc_map_filter : (string  * t -> t option) -> t -> t
+  (** Same as [assoc_map] but filters the output of [f].
+  *)
+
 val to_assoc : t -> (string * t) list
   (** Extract the items of a JSON object or raise [Type_error]. *)