package topojsone

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Sources and Sinks
Mapping
Folding

topojsone
- Topojsone
  - Err
  - Topojson
    
    Geometry
    
    Arc_index
    
    LineString
    
    MultiLineString
    
    MultiPoint
    
    MultiPolygon
    
    Point
    
    Polygon
    
    Position
    
    Topology

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A library for manipulating large TopoJSON documents without reading the whole document into memory using the Jsone streaming, JSON parser.

module Jsone = Geojsone.Jsone

module Ezjsone = Geojsone.Ezjsone

module Err : sig ... end

Topojsone comes with an implementation of a TopoJSON parser using Ezjsone. This is like Ezjsonm but uses Jsone for providing a non-blocking interface.

module Topojson : Topojson.S with type json = Ezjsone.value

Sources and Sinks

Topojsone is intended to be used with a non-blocking IO library using OCaml 5's effect support to provide a direct-style buffer filling and buffer writing functions.

Here's an example using the Eio library:

let src_of_flow ?(size = 2048) flow =
  let buff = Cstruct.create size in
  fun () ->
    let got = Eio.Flow.(single_read flow buff) in
    let t = Cstruct.sub buff 0 got in
    t

let with_src cwd f func =
  Eio.Path.(with_open_in (cwd / f)) @@ fun ic -> func @@ src_of_flow ic

let buffer_to_dst buf bs =
  Eio.Flow.(copy (cstruct_source [ bs ]) (Eio.Flow.buffer_sink buf))

Mapping

Maps are functions that allow you to manipulate common structure in TopoJson objects. These will be written directly back to the destination that you provide.

val map_object : 
  ((string * Topojson.Geometry.t) -> string * Topojson.Geometry.t) ->
  Jsone.src ->
  Jsone.dst ->
  (unit, Err.t) result

map_object f src dst will apply f to all TopoJson objects. The map will recurse into TopoJson Object. Note for the moment if you have a single geometry object as your document, this will not work.

Folding

val fold_object : 
  ('acc -> (string * Topojson.Geometry.t) -> 'acc) ->
  'acc ->
  Jsone.src ->
  ('acc, Err.t) result

fold_object f initial_acc src is much like map_object but allows you to accumulate some result that is then returned to you.