NodesIter.nodeEntries failed to typecheck

[dsiu]

open Graphology

let log = Console.log
let log2 = Console.log2

module Dict = Dict
module H = Graph.MakeGraph({
  type node = string
  type edge = string
})
let h = H.makeGraph()
"hi"->log
h->H.addNode("John", ~attr={"lastName": "Doe"})
h->H.addNode("Peter", ~attr={"lastName": "Egg"})
h->H.addNode("Mary")
h->H.addEdge("John", "Peter", ~attr={"dist": 23})
h->H.addEdge("Peter", "Mary", ~attr={"dist": 12})

let iter:it = h->H.NodesIter.nodeEntries
iter->log2("iter", _)

17 │ h->H.addEdge("Peter", "Mary", ~attr={"dist": 12})
  18 │ 
  19 │ let iter = h->H.NodesIter.nodeEntries
  20 │ iter->log2("iter", _)
  21 │ 

  This expression's type contains type variables that cannot be generalized:
  Iterator.t<H.NodesIter.nodeIterValue<{_..}>>
  
  This happens when the type system senses there's a mutation/side-effect,
  in combination with a polymorphic value.
  Using or annotating that value usually solves it.