Overview

Miso.Data.Map is a Haskell wrapper around the JavaScript Map object. Values of type Map k v live in JavaScript memory; all operations run in IO and mutate the underlying JS map in place.

Unlike Map, keys do not require an Ord instance — any type with a ToJSVal instance can serve as a key, including JS objects and numeric values that compare by identity.

Use this module when you need to share a key-value structure with a browser API or a third-party JavaScript library. For pure Haskell processing, prefer Map.

Import qualified to avoid clashing with Prelude:

import qualified Miso.Data.Map as M

Quick start

import qualified Miso.Data.Map as M

example :: IO ()
example = do
  m <- M.fromList [("a", 1), ("b", 2 :: Int)]
  M.insert "c" 3 m
  v <- M.lookup "b" m   -- Just 2
  n <- M.size m          -- 3
  M.delete "a" m
  pure ()

Operations

• Construction: new, fromList
• Access: lookup, has, size
• Mutation: insert, delete, clear

See also

• Miso.Data.Array — mutable JS Array
• Miso.Data.Set — mutable JS Set
• Miso.DSL — ToJSVal / FromJSVal used by key and value types