feat(decode): add indirect combinator to help with recursion (#6)

Author: glennsl

README.md

@@ -117,6 +117,9 @@ Please see [LICENSE.LGPL-3.0](https://github.com/glennsl/rescript-json-combinato
 
 ## Changes
 
+### 1.3.0
+- add `Decode.indirect` to help with decoding recursive data structures
+
 ### 1.2.0
 - add `Decode.flatMap`
 

examples/Recursive.res

@@ -0,0 +1,10 @@
+type rec t = {value: int, next: option<t>}
+
+module Decode = {
+  open Json.Decode
+
+  let rec list = () => object(field => {
+    value: field.required(. "value", int),
+    next: field.optional(. "next", indirect(list)),
+  })
+}

src/Json_Decode.res

@@ -242,6 +242,8 @@ let flatMap = (decodeA, f) => (. json) => {
   decodeB(. json)
 }
 
+let indirect = f => (. json) => f()(. json)
+
 let decode = (json, decode) =>
   try Ok(decode(. json)) catch {
   | DecodeError(msg) => Error(msg)

src/Json_Decode.resi

@@ -37,4 +37,6 @@ let oneOf: array<t<'a>> => t<'a>
 let map: (t<'a>, (. 'a) => 'b) => t<'b>
 let flatMap: (t<'a>, (. 'a) => t<'b>) => t<'b>
 
+let indirect: (() => t<'a>) => t<'a>
+
 let decode: (Js.Json.t, t<'a>) => result<'a, string>