Diogo Castro dcastro

$ cabal run exe:coffer -- create diogo/google-work \
  --field user:[email protected] \
  --field pw:123 \
  --field url:www.google.com

[SUCCESS] Entry created at '/diogo/google-work'

$ cabal run exe:coffer -- create diogo/google-home \

This tutorial assumes you're already familiar with Haskell's kind system and extensions like DataKinds. If not, please read my blog post first </shameless-plug>.

Say you want to model a TCP connection, and it can be in either an "open" or "closed" status.

data Connection = MkConnection ...

A type variable can be either universally ("for all x, then ...") or existentially quantified ("there exists some x, ...").

(If you're a maths persons, this corresponds to ∀x. x and ∃x. x, respectively)

In haskell, universally quantified type vars are represented with a forall:

head :: forall a. [a] -> Maybe a

	{
	"envelope_id": "f34c6197-a7ef-45ed-acad-4d5a3147ec86",
	"payload": {
	"token": "Pct6Sm6JynybrFXkjEiH7hhX",
	"team_id": "T02NDBHSWSG",
	"api_app_id": "A03BLN935DK",
	"event": {
	"type": "message",
	"subtype": "message_changed",
	"message": {

	{
	"envelope_id": "012327ef-4c84-41e3-a952-09af25782c17",
	"payload": {
	"token": "Pct6Sm6JynybrFXkjEiH7hhX",
	"team_id": "T02NDBHSWSG",
	"api_app_id": "A03BLN935DK",
	"event": {
	"client_msg_id": "0837851c-2d34-4d4d-804c-7aed753c3421",
	"type": "message",
	"text": "Hello world",

	>>>>0: https://hangzhou.testnet.tezos.serokell.team/version
	>>>>1: https://hangzhou.testnet.tezos.serokell.team/chains/main/blocks/head/protocols
	>>>>2: https://hangzhou.testnet.tezos.serokell.team/chains/main/blocks/head/context/contracts/tz1ZSedNyGuqibEYCPbuMS3yEhhLHfZEuLtA/counter
	>>>>3: https://hangzhou.testnet.tezos.serokell.team/chains/main/blocks/head/context/contracts/tz1ZSedNyGuqibEYCPbuMS3yEhhLHfZEuLtA/manager_key
	>>>>4: https://hangzhou.testnet.tezos.serokell.team/monitor/bootstrapped
	>>>>5: https://hangzhou.testnet.tezos.serokell.team/chains/main/blocks/head/context/constants
	>>>>6: https://hangzhou.testnet.tezos.serokell.team/chains/main/blocks/head/hash
	>>>>7: https://hangzhou.testnet.tezos.serokell.team/chains/main/chain_id
	>>>>8: https://hangzhou.testnet.tezos.serokell.team/chains/main/chain_id
	>>>>9: https://hangzhou.testnet.tezos.serokell.team/chains/main/blocks/head/helpers/scripts/simulate_operation

	$ nix-build ci.nix -A all-components --no-out-link


	building '/nix/store/bflfb6jrxykrp53fkd5f0gd0d45z776s-git-ls-files.drv'...
	trace: To make this a fixed-output derivation but not materialized, set `stack-sha256` to the output of /nix/store/w4f2lcmndg68m64cdrhm1vkhz2s216i7-calculateSha
	trace: To materialize the output entirely, pass a writable path as the `materialized` argument and pass that path to /nix/store/y1w6r7c4wrvhllzmz4k3h6g30b4hph74-generateMaterialized
	building '/nix/store/36nhcnn93ik0zdsmbcbrpqbq0ajl5lsc-morley-stack-to-nix-pkgs.drv'...
	substituteStream(): WARNING: pattern '/nix/store/fn96af9026mkyk28pj3ivwd9drzd247m-morley' doesn't match anything in file '/nix/store/zyzl3v6lww8a81qhmv052075a4qbbj7n-morley-stack-to-nix-pkgs/default.nix'
	substituteStream(): WARNING: pattern '/nix/store/fn96af9026mkyk28pj3ivwd9drzd247m-morley' doesn't match anything in file '/nix/store/zyzl3v6lww8a81qhmv052075a4qbbj7n-morley-stack-to-nix-pkgs/pkgs.nix'
	these derivations will be built:

	import Data.Vinyl (Rec(..))

	data Tag = TagInt \| TagPair Tag Tag

	data Exp (t :: Tag) where
	EInt :: Int -> Exp 'TagInt
	EPair :: Exp t1 -> Exp t2 -> Exp ('TagPair t1 t2)

	type family RightComb (tags :: [Tag]) :: Tag where
	RightComb '[ x, y ] = 'TagPair x y

	import Language.Haskell.TH.Lib
	import Language.Haskell.TH.Syntax

	module Problem where

	data PP a where
	PP :: forall a. Typeable a => PP a

	instance Lift (PP a) where
	lift PP = [\|PP\|]