jonsterling

Things About Interface Builder in No Particular Order

I have many other problems with Interface Builder beyond the ones here; these are just the ones that immediately came to mind. Likewise, however unsafe I have characterized IB to be in this tract, I assure you, it is far more unsafe than that.

Fragility: stringly styped code strikes again (bite me)

There are a number of places where IB-style stuff encourages unchecked stringly-typed code, and worse, the kind of stringly-typed code that doesn't allow you to use the same constant everywhere to provide some semblance of sanity.

1. Cell reuse identifiers.
2. Storyboard scene identifiers.

jonsterling

{-# OPTIONS --type-in-type  --no-positivity-check --no-termination-check #-}

module IndexingByCanonicity where

record Σ (A : Set) (B : A → Set) : Set where
  constructor _,_
  field
    π₁ : A
    π₂ : B π₁
open Σ public

jonsterling

1. Install libffi with my modified homebrew formula: https://github.com/jonsterling/homebrew/blob/master/Library/Formula/libffi.rb
2. export PKG_CONFIG_PATH=/usr/local/Cellar/libffi/3.0.13/lib/pkgconfig
3. cabal install libffi
4. cabal install idris

jonsterling

brew --config:

HOMEBREW_VERSION: 0.9.4
ORIGIN: https://github.com/mxcl/homebrew.git
HEAD: 0c1bf5fc5158d39e7e83ca2a779c4b4e9a2897fc
HOMEBREW_PREFIX: /usr/local
HOMEBREW_CELLAR: /usr/local/Cellar
CPU: quad-core 64-bit haswell
OS X: 10.8.4-x86_64

jonsterling

// RACCommand α β === Kleisli RACSignal α β === α -> RACSignal β
// We can pullback along the kleisli arrow to change the input to a command.
// Likewise, we can pushout along the arrow to change the output to a command.


RACSignal *validationSignal = self.form.validationSignal.replayLast;
UIBarButtonItem *doneButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemDone target:nil action:nil];
doneButton.rac_command = [self.viewModel.doneCommand ys_pullback:^RACSignal *(id input) {
  return [validationSignal take:1];
}];

jonsterling

typedef RACSignal *(^RACSignalKleisliBlock)(id input);

@interface RACSignalKleisli : NSObject
- (id)initWithSignalBlock:(RACSignalKleisliBlock)block;
- (instancetype)compose:(RACSignalKleisli *)kleisli;
- (RACSignal *)execute:(id)input;
@end

@implementation RACSignalKleisli {
	RACSignalBlock _signalBlock;

jonsterling

RACCommand *example = [[RACCommand alloc] initWithSignalBlock:^(id input) { 
  return [RACSignal createWithBlock:^(id<RACSubscriber> subscriber){ 
    [subscriber sendCompleted]; 
    return nil; 
  }];
];

// Now, how will I know when each task has completed?
// I certainly cannot tell from `example.executionSignals.flatten`.

jonsterling

module type TYPE = sig
  type t
end

module type EMPTY = functor (T : TYPE) -> sig
  val apply : T.t
end

type empty = (module EMPTY)

jonsterling

// A nice little example of using transactional signal generators.
// Imagine a board of buttons with numbers on it, and a big red button with a picture of a bomb on it.
// When a button with a number is pressed, `increment` is invoked with that number. When the bomb
// button is pressed, then `reset` is invoked.
//
//This returns a signal of the running total made by incrementing by numbers and resetting by explosions.
RACDynamicSignalGenerator *increment = [[RACDynamicSignalGenerator alloc] initWithBlock:^RACSignal *(NSNumber *add) {
	return [RACSignal return:^(NSNumber *count) {
		return @(count.integerValue + add.integerValue);
	}];

jonsterling

(* It is not possible in Standard ML to construct an identity type (or any other
 * indexed type), but that does not stop us from speculating. We can specify with
 * a signature equality should mean, and then use a functor to say, "If there
 * were a such thing as equality, then we could prove these things with it."
 * Likewise, we can use the same trick to define the booleans and their
 * induction principle at the type-level, and speculate what proofs we could
 * make if we indeed had the booleans and their induction principle.
 *
 * Functions may be defined by asserting their inputs and outputs as
 * propositional equalities in a signature; these "functions" do not compute,