dino-

#! /usr/bin/env runhaskell

import Text.HTML.TagSoup

main :: IO ()
main = do
   tags <- fmap parseTags $ readFile "foo.xml";
   let names = sections (~== "<name>") $ tags
   mapM_ (\t -> putStrLn $ "saw: " ++ t ) $ map fromTagText
      $ map (flip (!!) 1) names

dino-

The interesting type of foldl (flip id)

System.Console.GetOpt

Going through the example code for System.Console.GetOpt got me thinking about the type of foldl (flip id)

Specifically, the second example Interpreting flags as transformations of an options record. The code is using this to combine all of the command-line args into a record of the args as a whole.

I was confused about how foldl (flip id) has the type it does

dino-

In Haskell, it's sometimes useful to turn off buffering when writing code that uses the standard input/output file handles. That can be done to the three commonly-used handles in one line like this:

  import System.IO

  mapM_ (flip hSetBuffering NoBuffering) [ stdout, stderr, stdin ]

It's kind of terse though, let's go through what's happening in it.

dino-

#!/usr/bin/env stack
-- stack --resolver lts-12.24 script

-- If stack isn't installed on your system and you can't/won't get it, install
-- a reasonably-modern GHC and use this instead of the above two lines:
-- #! /usr/bin/env runhaskell

import Control.Monad.State

dino-

#! /usr/bin/env stack
-- stack --resolver lts-18.8 script

{-# LANGUAGE OverloadedStrings #-}

{-
This is a handy illustration of converting between five of the commonly-used
string types in Haskell (String, ByteString, lazy ByteString, Text and lazy
Text).

dino-

#! /usr/bin/env stack
-- stack --resolver lts-13.15 runghc --package mtl

{-# LANGUAGE FlexibleContexts #-}

import Control.Monad.Except


main :: IO ()
main = do

dino-

Keybase proof

I hereby claim:

• I am dino- on github.
• I am dino733 (https://keybase.io/dino733) on keybase.
• I have a public key ASCV2424hXHoyxWn_lBsR3WEbtttYO4BTEUHwjNPPupxxQo

To claim this, I am signing this object:

dino-

import Control.Monad ( void )
import Data.Aeson ( FromJSON, ToJSON )
import qualified Data.Text as T
import GHC.Generics ( Generic )
import Language.Plutus.Contract
import Language.PlutusTx as PlutusTx
import Language.PlutusTx.Prelude
import Ledger
import Ledger.Ada as Ada
import Ledger.Constraints as Constraints

dino-

Haskell symbols

When starting out with Haskell, I found it difficult to read a lot of the symbols. I made this document explaining the names of some symbols and how I read them.

:: "has type"

x :: Int

dino-

// A JavaScript promises cheat-sheet


// an immediately resolved promise
const p1 = Promise.resolve('foo');

// can get it after the fact, unlike events
p1.then((res) => console.log('p1 got:', res));
// => p1 got: foo