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-- This gist shows how we can use abilities to provide nicer syntax for any monad.
-- We can view abilities as "just" providing nicer syntax for working with the
-- free monad.

ability Monadic f where
  eval : f a -> a

-- Here's a monad, encoded as a first-class value with
-- two polymorphic functions, `pure` and `bind`
type Monad f = Monad (forall a . a -> f a) (forall a b . f a -> (a -> f b) -> f b)

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module Elmz.Layout where

import List
import Array (Array)
import Either(..)
import Graphics.Element as E
import Graphics.Element (Direction, Element, Position)

type Pt = { x : Int, y: Int }

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// WARNING! totally untested, I have only compiled the code! :)

package json

import collection.immutable.Map
import scalaz.{\/, MonadPlus}
import scalaz.\/._
import scalaz.std.vector._
import scalaz.std.map._
import scalaz.std.list._

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unique ability Batch where
  increment : Nat -> () 

-- Like `State.transact`, but pauses the computation every `batchSize` calls to 
-- `Batch.increment` and commits the work so far in one transaction, then resumes
-- the rest of the computation.
State.transact.batched : Nat -> Database -> '{Batch, Transaction, Exception} a ->{State, Exception} a
State.transact.batched batchSize db b = 
  go : Nat -> Request {Batch} a -> Either ('{Batch,Transaction,Exception} a) a
  go acc = cases

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Take-home functional programming interview

This document is licensed CC0.

These are some questions to give a sense of what you know about FP. This is more of a gauge of what you know, it's not necessarily expected that a single person will breeze through all questions. For each question, give your answer if you know it, say how long it took you, and say whether it was 'trivial', 'easy', 'medium', 'hard', or 'I don't know'. Give your answers in Haskell for the questions that involve code.

Please be honest, as the interviewer may do some spot checking with similar questions. It's not going to look good if you report a question as being 'trivial' but a similar question completely stumps you.

Here's a bit more guidance on how to use these labels:

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use data Array

structural type Sequence a
  = Empty Nat
  | Sequence Nat Nat (Array a) (Sequence (Array a)) (Array a)

Sequence.arity : Sequence a -> Nat
Sequence.arity = cases
  Sequence.Empty arity   -> arity
  Sequence arity _ _ _ _ -> arity

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This is material to go along with a 2014 Boston Haskell talk.

We are going to look at a series of type signatures in Haskell and explore how parametricity (or lack thereof) lets us constrain what a function is allowed to do.

Let's start with a decidedly non-generic function signature. What are the possible implementations of this function which typecheck?

wrangle :: Int -> Int

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Here's a transcript of me updating a dependency in Unison. We're going to make this more streamlined, but this is the process for now. First, I made a copy of the branch I was updating (in this case main of distributed):

.distributed> fork main topics.baseupdate

  Done.

Next I pulled the new version of base into lib.base_new:

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unique type test.Result = Fail Failure | Ok Text

unique ability Weighted a where
  bump : Nat -> ()
  give : a -> ()

unique ability Gen where
  generate : '{Weighted a} () -> a

Weighted.map : (a ->{g} b) -> '{Weighted a, g} r -> '{Weighted b,g} r 

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-- id is the doc id, a is the text type, v is the value type
unique type Trie id txt
  = Remainder txt (Trie.Pos id)
  | Branch Nat (Dataset Value (Trie.Pos id)) (Map txt (Value (Trie id txt)))
  --Remainder id txt Nat
  -- there can be multiple docs at this suffix
  -- Branch size 
  --| Branch Nat (Dataset Value id) (Map txt (Value (Trie id txt)))

unique type Trie.Pos id = Pos id Nat