Декларативное программирование и алгебраические типы данных в примерах для Django

Максим Аванов (Shopitize)

Рассказ о том, как базовые примитивы декларативного программирования одновременно избавляют от boilerplate-кода и контролируют согласованность логики гипотетического приложения на Django.

Transcript

1. Declarative Programming & Algebraic Data Types * Maxim Avanov maximavanov.com * from Django's perspective 19th Moscow Django Meetup
2. Our Goal 1. «Outsource» boilerplate (i.e. concentrate on important). 2. Check as much as possible, and as soon as possible. 3. Component coherence.
3. 1. A story of How & What Concentrate on important
4. How vs. What d e f h a n d l e _ a r t i c l e _ f o r m ( r e q u e s t ) : i f r e q u e s t . m e t h o d = = ' P O S T ' : f o r m = A r t i c l e F o r m ( r e q u e s t . P O S T ) i f f o r m . i s _ v a l i d ( ) : s a v e _ a r t i c l e ( f o r m . c l e a n e d _ d a t a ) r e t u r n H t t p R e s p o n s e R e d i r e c t ( ' / s u c c e s s / ' ) e l s e : f o r m = A r t i c l e F o r m ( ) r e t u r n r e n d e r ( r e q u e s t , ' a r t i c l e _ f o r m . h t m l ' , { ' f o r m ' : f o r m } )
5. How i f r e q u e s t . m e t h o d = = ' P O S T ' : f o r m = A r t i c l e F o r m ( r e q u e s t . P O S T ) i f f o r m . i s _ v a l i d ( ) : # . . . e l s e : # . . . What # c a s e 1 s a v e _ a r t i c l e ( f o r m . c l e a n e d _ d a t a ) r e t u r n H t t p R e s p o n s e R e d i r e c t ( ' / s u c c e s s / ' ) # c a s e 2 f o r m = A r t i c l e F o r m ( ) r e t u r n r e n d e r ( r e q u e s t , ' a r t i c l e _ f o r m . h t m l ' , { ' f o r m ' : f o r m } )
6. A few things to worry about d e f h a n d l e _ a r t i c l e _ f o r m ( r e q u e s t ) : i f r e q u e s t . m e t h o d = = ' P O S T ' : f o r m = A r t i c l e F o r m ( r e q u e s t . P O S T ) i f f o r m . i s _ v a l i d ( ) : s a v e _ a r t i c l e ( f o r m . c l e a n e d _ d a t a ) r e t u r n H t t p R e s p o n s e R e d i r e c t ( ' / s u c c e s s / ' ) e l s e : f o r m = A r t i c l e F o r m ( ) r e t u r n r e n d e r ( r e q u e s t , ' a r t i c l e _ f o r m . h t m l ' , { ' f o r m ' : f o r m } ) «What» is obscured by «How» redundant details Single Responsibility principle is violated
7. If we could get rid of How's once and for all, would we miss them?
8. Constraint programming
9. Tribute to Pyramid f r o m r h e t o r i c i m p o r t v i e w _ c o n f i g , v i e w _ d e f a u l t s @ v i e w _ d e f a u l t s ( r o u t e _ n a m e = ' a r t i c l e s ' , r e n d e r e r = ' a r t i c l e _ f o r m . h t m l ' ) c l a s s A r t i c l e s H a n d l e r ( o b j e c t ) : d e f _ _ i n i t _ _ ( s e l f , r e q u e s t ) : s e l f . r e q u e s t = r e q u e s t @ v i e w _ c o n f i g ( r e q u e s t _ m e t h o d = ' G E T ' ) d e f a r t i c l e _ f o r m ( s e l f ) : f o r m = A r t i c l e F o r m ( ) r e t u r n { ' f o r m ' : f o r m } @ v i e w _ c o n f i g ( r e q u e s t _ m e t h o d = ' P O S T ' , v a l i d a t e _ f o r m = A r t i c l e F o r m ) d e f s a v e _ a r t i c l e ( s e l f ) : s a v e _ a r t i c l e ( s e l f . r e q u e s t . f o r m . c l e a n e d _ d a t a ) r e t u r n H t t p R e s p o n s e R e d i r e c t ( ' / s u c c e s s / ' ) @ v i e w _ c o n f i g ( r e q u e s t _ m e t h o d = ' P O S T ' ) d e f i n v a l i d _ a r t i c l e _ f o r m ( s e l f ) : r e t u r n { ' f o r m ' : s e l f . r e q u e s t . f o r m }
10. What it actually means # W e h a v e a n A r t i c l e s H a n d l e r : A r t i c l e s H a n d l e r # I t r e n d e r s a t e m p l a t e : a r t i c l e _ f o r m . h t m l # A u s e r s h a l l b e a b l e t o a d d n e w e n t r i e s : a r t i c l e _ f o r m ( ) # I f w e s u b m i t v a l i d A r t i c l e F o r m : s a v e _ a r t i c l e ( ) # I f w e s u b m i t i n v a l i d A r t i c l e F o r m : i n v a l i d _ a r t i c l e _ f o r m ( ) c l a s s A r t i c l e s H a n d l e r ( o b j e c t ) : d e f _ _ i n i t _ _ ( s e l f , r e q u e s t ) : s e l f . r e q u e s t = r e q u e s t d e f a r t i c l e _ f o r m ( s e l f ) : f o r m = A r t i c l e F o r m ( ) r e t u r n { ' f o r m ' : f o r m } d e f s a v e _ a r t i c l e ( s e l f ) : s a v e _ a r t i c l e ( s e l f . r e q u e s t . f o r m . c l e a n e d _ d a t a ) r e t u r n H t t p R e s p o n s e R e d i r e c t ( ' / s u c c e s s / ' ) d e f i n v a l i d _ a r t i c l e _ f o r m ( s e l f ) : r e t u r n { ' f o r m ' : s e l f . r e q u e s t . f o r m }
11. ...or in other words - - - v i e w : A r t i c l e s H a n d l e r G E T : a r t i c l e _ f o r m P O S T : - v a l i d a t e : a r t i c l e s . A r t i c l e F o r m v i e w : s a v e _ a r t i c l e - v i e w : i n v a l i d _ a r t i c l e _ f o r m c l a s s A r t i c l e s H a n d l e r ( o b j e c t ) : d e f _ _ i n i t _ _ ( s e l f , r e q u e s t ) : s e l f . r e q u e s t = r e q u e s t d e f a r t i c l e _ f o r m ( s e l f ) : f o r m = A r t i c l e F o r m ( ) r e t u r n { ' f o r m ' : f o r m } d e f s a v e _ a r t i c l e ( s e l f ) : s a v e _ a r t i c l e ( s e l f . r e q u e s t . f o r m . c l e a n e d _ d a t a ) r e t u r n H t t p R e s p o n s e R e d i r e c t ( ' / s u c c e s s / ' ) d e f i n v a l i d _ a r t i c l e _ f o r m ( s e l f ) : r e t u r n { ' f o r m ' : s e l f . r e q u e s t . f o r m }
12. A couple of other examples
13. Different ways to do the same thing @ v i e w _ d e f a u l t s ( r o u t e _ n a m e = ' a u t h e n t i c a t i o n ' , r e n d e r e r = ' a u t h _ f o r m . h t m l ' ) c l a s s A u t h e n t i c a t i o n H a n d l e r ( o b j e c t ) : @ v i e w _ c o n f i g ( r e q u e s t _ m e t h o d = ' P O S T ' , v a l i d a t e _ f o r m = E m a i l A u t h F o r m ) d e f a u t h _ w i t h _ e m a i l ( s e l f ) : # . . . @ v i e w _ c o n f i g ( r e q u e s t _ m e t h o d = ' P O S T ' , v a l i d a t e _ f o r m = S M S A u t h F o r m ) d e f a u t h _ w i t h _ s m s ( s e l f ) : # . . . @ v i e w _ c o n f i g ( r e q u e s t _ m e t h o d = ' P O S T ' , v a l i d a t e _ f o r m = L o g i n A u t h F o r m ) d e f a u t h _ w i t h _ l o g i n ( s e l f ) : # . . . @ v i e w _ c o n f i g ( r e q u e s t _ m e t h o d = ' P O S T ' ) d e f o n _ i n v a l i d _ f o r m ( s e l f ) : # . . .
14. API versioning c o n f i g . a d d _ r o u t e ( ' a p i . w o r k f l o w s ' , ' / a p i / w o r k f l o w s ' ) @ v i e w _ d e f a u l t s ( r o u t e _ n a m e = ' a p i . w o r k f l o w s ' , a p i _ v e r s i o n = ' < 2 . 0 ' ) c l a s s W o r k f l o w s A P I v 1 ( o b j e c t ) : # . . . @ v i e w _ d e f a u l t s ( r o u t e _ n a m e = ' a p i . w o r k f l o w s ' , a p i _ v e r s i o n = ' > = 2 . 0 ' ) c l a s s W o r k f l o w s A P I v 2 ( o b j e c t ) : # . . . @ v i e w _ d e f a u l t s ( r o u t e _ n a m e = ' a p i . w o r k f l o w s ' , r e n d e r e r = ' j s o n ' ) c l a s s W o r k f l o w s A P I ( o b j e c t ) : @ v i e w _ c o n f i g ( r e q u e s t _ m e t h o d = ' P O S T ' , a p i _ v e r s i o n = ' < 2 . 0 ' ) d e f c r e a t e _ n e w _ w o r k f l o w _ v 1 ( s e l f ) : # . . . @ v i e w _ c o n f i g ( r e q u e s t _ m e t h o d = ' P O S T ' , a p i _ v e r s i o n = ' > = 2 . 0 ' ) d e f c r e a t e _ n e w _ w o r k f l o w _ v 2 ( s e l f ) : # . . .
15. Algebraic Data Types
16. OCaml ADT example Watch a «Caml Trading» talk by Yaron Minsky at http://youtu.be/hKcOkWzj0_s?t=31m6s
17. OCaml ADT example t y p e o r d e r = { i d : i n t ; p r i c e : f l o a t ; s i z e : i n t ; } t y p e c a n c e l = { x i d : i n t ; } t y p e i n s t r u c t i o n = | O r d e r o f o r d e r | C a n c e l o f c a n c e l l e t f i l t e r _ b y _ o i d i n s t r u c t i o n s o i d = L i s t . f i l t e r i n s t r u c t i o n s ( f u n x - > m a t c h x w i t h | O r d e r o - > o . i d = o i d | C a n c e l c - > c . x i d = o i d )
18. OCaml ADT example t y p e o r d e r = { i d : i n t ; p r i c e : f l o a t ; s i z e : i n t ; } t y p e c a n c e l = { x i d : i n t ; } t y p e c a n c e l _ r e p l a c e = { x r _ i d : i n t ; n e w _ p r i c e : f l o a t ; n e w _ s i z e : i n t ; } t y p e i n s t r u c t i o n = | O r d e r o f o r d e r | C a n c e l o f c a n c e l | C a n c e l _ r e p l a c e o f c a n c e l _ r e p l a c e l e t f i l t e r _ b y _ o i d i n s t r u c t i o n s o i d = L i s t . f i l t e r i n s t r u c t i o n s ( f u n x - > m a t c h x w i t h | O r d e r o - > o . i d = o i d | C a n c e l c - > c . x i d = o i d ) W a r n i n g P : T h i s p a t t e r n - m a t c h i n g i s n o t e x h a u s t i v e H e r e i s a n e x a m p l e o f a v a l u e t h a t i s n o t m a t c h e d . . .
19. 2. Trying to reproduce Check as much as possible, and as soon as possible
20. Python ADT * * kind of
21. Python ADT example Models (product types) f r o m d j a n g o . d b i m p o r t m o d e l s c l a s s O r d e r ( m o d e l s . M o d e l ) : t i d = m o d e l s . I n t e g e r F i e l d ( ) p r i c e = m o d e l s . D e c i m a l F i e l d ( m a x _ d i g i t s = 1 6 , d e c i m a l _ p l a c e s = 4 ) s i z e = m o d e l s . I n t e g e r F i e l d ( ) c l a s s C a n c e l ( m o d e l s . M o d e l ) : x t i d = m o d e l s . I n t e g e r F i e l d ( ) c l a s s C a n c e l R e p l a c e ( m o d e l s . M o d e l ) : x r _ t i d = m o d e l s . I n t e g e r F i e l d ( ) n e w _ p r i c e = m o d e l s . D e c i m a l F i e l d ( m a x _ d i g i t s = 1 6 , d e c i m a l _ p l a c e s = 4 ) n e w _ s i z e = m o d e l s . I n t e g e r F i e l d ( )
22. Python ADT example Smart Enums (union types) f r o m r h e t o r i c . a d t i m p o r t a d t f r o m . m o d e l s i m p o r t O r d e r , C a n c e l , C a n c e l R e p l a c e c l a s s I n s t r u c t i o n ( a d t ) : O R D E R = O r d e r C A N C E L = C a n c e l C A N C E L _ R E P L A C E = C a n c e l R e p l a c e
23. Python ADT example Cases (match statement) f r o m . t y p e s i m p o r t I n s t r u c t i o n @ I n s t r u c t i o n . O R D E R ( ' f i l t e r _ b y _ o i d ' ) d e f f i l t e r _ o r d e r _ b y _ o i d ( o r d e r , o i d ) : r e t u r n o r d e r . t i d = = o i d @ I n s t r u c t i o n . C A N C E L ( ' f i l t e r _ b y _ o i d ' ) d e f f i l t e r _ c a n c e l _ b y _ o i d ( c a n c e l , o i d ) : r e t u r n c a n c e l . x t i d = = o i d @ I n s t r u c t i o n . C A N C E L _ R E P L A C E ( ' f i l t e r _ b y _ o i d ' ) d e f f i l t e r _ c a n c e l _ r e p l a c e _ b y _ o i d ( c r , o i d ) : r e t u r n c r . x r _ t i d = = o i d d e f f i l t e r _ b y _ o i d ( i n s t r u c t i o n s , o i d ) : r e t u r n l i s t ( f i l t e r ( l a m b d a i : I n s t r u c t i o n . m a t c h ( i ) [ ' f i l t e r _ b y _ o i d ' ] ( i , o i d ) , i n s t r u c t i o n s ) )
24. Python ADT example Cases (2) f r o m . t y p e s i m p o r t I n s t r u c t i o n i n l i n e _ m a t c h e r = I n s t r u c t i o n . i n l i n e _ m a t c h ( O R D E R = ( l a m b d a o , o i d : o . t i d = = o i d ) , C A N C E L = ( l a m b d a c , o i d : c . x t i d = = o i d ) , C A N C E L _ R E P L A C E = ( l a m b d a c r , o i d : c r . x r _ t i d = = o i d ) ) d e f f i l t e r _ b y _ o i d _ a l t ( i n s t r u c t i o n s , o i d ) : r e t u r n l i s t ( f i l t e r ( l a m b d a i : i n l i n e _ m a t c h e r ( i ) ( i , o i d ) , i n s t r u c t i o n s ) )
25. 3. Use case: multilingual content Component coherence
26. Use case Define ADT f r o m r h e t o r i c . a d t i m p o r t a d t c l a s s L a n g u a g e ( a d t ) : E N G L I S H = ' e n ' G E R M A N = ' d e '
27. Use case Register Models f r o m d j a n g o . d b i m p o r t m o d e l s f r o m . t y p e s i m p o r t L a n g u a g e c l a s s I R e g i o n a l A r t i c l e ( m o d e l s . M o d e l ) : c l a s s M e t a : a b s t r a c t = T r u e t i t l e = m o d e l s . C h a r F i e l d ( m a x _ l e n g t h = 1 4 0 , d e f a u l t = ' ' ) t e x t = m o d e l s . T e x t F i e l d ( m a x _ l e n g t h = 6 5 5 3 6 , d e f a u l t = ' ' ) @ L a n g u a g e . E N G L I S H ( ' d b : a r t i c l e s ' ) c l a s s E n g l i s h A r t i c l e ( I R e g i o n a l A r t i c l e ) : p a s s @ L a n g u a g e . G E R M A N ( ' d b : a r t i c l e s ' ) c l a s s G e r m a n A r t i c l e ( I R e g i o n a l A r t i c l e ) : p a s s
28. Use case Process requests f r o m r h e t o r i c . v i e w i m p o r t v i e w _ c o n f i g , v i e w _ d e f a u l t s f r o m . t y p e s i m p o r t L a n g u a g e @ v i e w _ d e f a u l t s ( r o u t e _ n a m e = ' a r t i c l e s . r e g i o n a l . i n d e x ' , r e n d e r e r = ' j s o n ' ) c l a s s A r t i c l e s H a n d l e r ( o b j e c t ) : d e f _ _ i n i t _ _ ( s e l f , r e q u e s t , l a n g u a g e ) : s e l f . r e q u e s t = r e q u e s t s e l f . l a n g u a g e = l a n g u a g e s e l f . l a n g u a g e _ s t r a t e g y = L a n g u a g e . m a t c h ( l a n g u a g e ) @ v i e w _ c o n f i g ( r e q u e s t _ m e t h o d = ' G E T ' ) d e f s h o w _ l o c a l _ e n t r i e s ( s e l f ) : r e t u r n { ' o k ' : T r u e }
29. Consistency check Adding a new language c l a s s L a n g u a g e ( a d t ) : E N G L I S H = ' e n ' G E R M A N = ' d e ' S P A N I S H = ' e s ' C o n f i g u r a t i o n E r r o r : C a s e d b : a r t i c l e s o f < c l a s s ' p r o j e c t . a r t i c l e s . t y p e s . L a n g u a g e ' > i s n o t e x h a u s t i v e . H e r e i s t h e v a r i a n t t h a t i s n o t m a t c h e d : S P A N I S H # W e h a v e t o r e g i s t e r t h i s c a s e @ L a n g u a g e . S P A N I S H ( ' d b : a r t i c l e s ' ) c l a s s S p a n i s h A r t i c l e ( I R e g i o n a l A r t i c l e ) : p a s s
30. Consistency check Using undefined variant f r o m r h e t o r i c . a d t i m p o r t a d t c l a s s L a n g u a g e ( a d t ) : E N G L I S H = ' e n ' G E R M A N = ' d e ' i n l i n e _ m a t c h e r = L a n g u a g e . i n l i n e _ m a t c h ( E N G L I S H = l a m b d a : E n g l i s h A r t i c l e . o b j e c t s . a l l ( ) , G E R M A N = l a m b d a : G e r m a n A r t i c l e . o b j e c t s . a l l ( ) , S P A N I S H = l a m b d a : S p a n i s h A r t i c l e . o b j e c t s . a l l ( ) ) P a t t e r n E r r o r : V a r i a n t S P A N I S H d o e s n o t b e l o n g t o t h e t y p e < c l a s s ' p r o j e c t . a r t i c l e s . t y p e s . L a n g u a g e ' >
31. Consistency check Guard boundaries f r o m . t y p e s i m p o r t L a n g u a g e d e f i n c l u d e m e ( c o n f i g ) : R U L E S = { ' l a n g u a g e ' : L a n g u a g e } c o n f i g . a d d _ r o u t e ( ' a r t i c l e s . r e g i o n a l . i n d e x ' , ' / a r t i c l e s / { l a n g u a g e } ' , R U L E S ) / a r t i c l e s / { l a n g u a g e } = > ^ a r t i c l e s / ( ? P < l a n g u a g e > ( ? : d e | e n ) ) $ c l a s s L a n g u a g e ( a d t ) : E N G L I S H = ' e n ' G E R M A N = ' d e ' S P A N I S H = ' e s ' / a r t i c l e s / { l a n g u a g e } = > ^ a r t i c l e s / ( ? P < l a n g u a g e > ( ? : d e | e n | e s ) ) $
32. Use case Strategy map c l a s s A r t i c l e s H a n d l e r ( o b j e c t ) : d e f _ _ i n i t _ _ ( s e l f , r e q u e s t , l a n g u a g e ) : s e l f . r e q u e s t = r e q u e s t s e l f . l a n g u a g e = l a n g u a g e s e l f . l a n g u a g e _ s t r a t e g y = L a n g u a g e . m a t c h ( l a n g u a g e ) G E T / a r t i c l e s / d e { ' d b : a r t i c l e s ' : < c l a s s ' p r o j e c t . a r t i c l e s . m o d e l s . G e r m a n A r t i c l e ' > } G E T / a r t i c l e s / e n { ' d b : a r t i c l e s ' : < c l a s s ' p r o j e c t . a r t i c l e s . m o d e l s . E n g l i s h A r t i c l e ' > }
33. Beyond today's topic Things worth mentioning github.com/lihaoyi/macropy github.com/benanhalt/PyAlgebraicDataTypes (cons ADT) «Say What You Mean» talk by Ryan Kelly
34. Thank you Q & A
35. Credits talk by Yaron Minsky «Caml Trading» Rhetoric Project Venusian Project