miso

Platform

MisoString

MisoString is miso's canonical string type, chosen to minimise copying between the Haskell and JavaScript heaps.

  • JS / WASM backends — MisoString is JSString, a direct reference to a JavaScript string; no marshalling cost when passing to the DOM or FFI.
  • Server / vanilla GHC (-fssr) — MisoString is Data.Text.

Use MisoString anywhere you would otherwise reach for String or Text in a miso application. See Miso.String for the full API (it re-exports the underlying module wholesale).

Converting to MisoString

ms (shorthand for toMisoString) converts any type with a ToMisoString instance:

ms "hello"          -- String -> MisoString
ms (42 :: Int)      -- Int    -> MisoString
ms (3.14 :: Double) -- Double -> MisoString
ms myText           -- Text   -> MisoString

Instances exist for String, strict and lazy Text, ByteString, Int, Word, Double, Float and Char.

Converting from MisoString

fromMisoString parses back into another type (throwing on failure); fromMisoStringEither is the safe variant:

fromMisoString "42"     :: Int     -- 42
fromMisoString "3.14"   :: Double  -- 3.14
fromMisoStringEither s  :: Either String Int

Multiline literals

GHC's MultilineStrings extension (9.12+) works directly with MisoString — this site uses it for all of its code samples:

{-# LANGUAGE MultilineStrings #-}

snippet :: MisoString
snippet = """
  line one
  line two
  """

On older compilers, Miso.String.QQ provides the misoString quasi-quoter for the same purpose.