Contracts in Clojure: the best-yet compromise between types and tests. As delivered at Philly ETE, April 7, 2015

1. @jessitron
es!
Tests!
Clojure!
Contracts
in

2. Contracts and Clojure:
the Best-Yet Compromise
Between
Types and Tests
Philly ETE, 7 April 2015

3. What do we know?
How do we know it?
…
This code works!

4. Formal
Proofs
Informal
Reasoning
Experimental
Evidence

5. def formatReport(data: ReportData): ExcelSheet
// Scala

6. types

8. (defn format-report [report-data]
…)

9. (defn ad-performance-report [params]
(-> (fetch-events params)
(analyze-ad-performance params)
format-report))

10. (defn ad-performance-report [params]
(-> (fetch-events params)
(analyze-ad-performance params)
format-report))

11. (defn analyze-ad-performance [events params]
(-> events
(group-up params)
summarize
add-total-row
(add-headers params)))

12. {:when 12:34:56 7/8/90
:what "show"
:who "abc123"}

13. {:when org.joda.time.DateTime
:what java.lang.String
:who java.lang.String}
(def Event
)

14. (def Event
)
{:when DateTime
:what s/Str
:who s/Str}
(:require [schema.core :as s])

15. (def Event
)
{:when DateTime
:what Incident
:who Customer}
(:require [schema.core :as s])
Event

16. (def Event
)
{:when DateTime
:what Incident
:who Customer}
(:require [schema.core :as s])
[Event]

17. [Event]
(defn ad-performance-report [params]
(-> (fetch-events params)
(analyze-ad-performance params)
format-report))

18. [Event]
…)
(s/defn fetch-events [params]

19. [Event]
(:require [schema.core :as s])
…)
(s/defn fetch-events
[params]
:-

20. (deftest fetch-events-test
…
(= (expected (fetch-events input))))

21. (deftest fetch-events-test
…
(= (expected (fetch-events input))))
(use-fixtures schema.test/validate-schemas)

22. (def Event
)
{:when DateTime
:what Incident
:who Customer}
(:require [schema.core :as s])
[Event]

23. (def Event
)
{:when DateTime
:what Incident
:who Customer}
(:require [schema.core :as s])
[Event] [[Event]]

24. [Event] [[Event]][Event]

25. [Event] [[Event]]
[Event]

26. [Event] [[Event]]
[[Event] Summation]

27. [Event]
[( one [Event] )
( one Summation )]
[[Event]]

28. [Event]
[(s/one [Event] "event list")
(s/one Summation "group sum")]
[[Event]]

29. (def Group
)
[Event]
[(s/one [Event] "event list")
(s/one Summation "group sum")]
[[Event]] [Group]

30. [Event] [[Event]]
{:groups [Group]}

31. [Event] [[Event]]
{:groups [Group]
:totals Totals}

32. [Event] [[Event]]
{:header Headers
:groups [Group]
:totals Totals}

33. [Event] [[Event]]
{:header Headers
:groups [Group]
:totals Totals}
(def ReportData
)

34. {:header Headers
:groups [Group]
:totals Totals}
(def ReportData
)

35. ReportData(s/defn analyze-ad-performance :-
[events :-
params :- Params]
(-> events
(group-up params)
summarize
add-total-row
(add-headers params)))
[Event]

36. (deftest analyze-ad-performance-test
(testing "grouping of rows"
(let […
result (analyze-ad-performance
events
{})
(is (= expected (:groups result))))))

37. (deftest analyze-ad-performance-test
(testing "grouping of rows"
(let […
result (analyze-ad-performance
events
{})
(is (= expected (:groups result))))))
(use-fixtures schema.test/validate-schemas)

38. result (analyze-ad-performance
events
{})
(is (= expected (:groups result))))))
Input does not match schema Params
Missing required key :title
Missing required key :start
Missing required key :end

39. :title string
:start date
:end date
Params

40. tle string
art date
nd date
:title string
:start date
:end date
param-gen

41. n't empty
end date
now
:title string
:start date
:end date
:title string
:start date
:end date
param-gen

42. :title string that isn't empty
:start date before end date
:end date before now
:
:
:
param-gen

43. (deftest analyze-ad-performance-test
(testing "grouping of rows"
(let […
result (analyze-ad-performance
[events]
(sample-one param-gen))
(is (= expected (:groups result))))))

44. (defspec analyze-ad-performance-spec 100
(for-all [events events-gen
params param-gen]
(analyze-ad-performance events params))))

45. Q: What do we know?
A: Schemas
Q: How do we know it?
A: Generative Tests

46. Q: What do we know?
data shape

47. We live in this weird time where a rose by any other name
throws a compile/runtime error. @deech

48. Q: What do we know?
data shape
data value boundaries

49. :title
- string
- not empty
- capitalized
Headers

50. (def Headers
{:title
(s/both
s/Str
(s/pred (complement empty?) "nonempty")
(s/pred capitalized? "Title Caps"))
…})

51. Q: What do we know?
data shape
value boundaries
relationships within values

52. {:title …
:start DateTime
:end DateTime}
- start is before end
Headers

53. Q: What could we know?
produced types

54. (s/def params :- (generator-of Params)
(gen/hash-map
:title …
:start …
:end …))
what
if?

55. (defgen params Params (gen/hash-map
:title …
:start …
:end …))
what
if?

56. (defgen params Params (gen/hash-map
:title …
:start …
:end …))
what
if?
Generator: my-project.generators/params
Value: {:end #<DateTime -58693684-08-30T03:25:35.104Z>, :
Error: (not (keyword? a-clojure.lang.PersistentArrayMap))

57. (s/defn fetch-events :- [Event]
[params]
…)

58. (s/defn fetch-events :- (lazy-seq-of Event)
[params]
…)
what
if?

59. Generator of A
Function from A to B
Lazy sequence of A

60. Q: What could we know?
produced types
relationships between types

61. (s/defn sample-one [A :- Schema]
(s/fn :- A [g :- (generator-of A)]
(last (gen/sample g))))
((sample-one Params) params-gen)

62. (tdefn sample-one :- A
[A :- Schema
g :- (generator-of A)]
(last (gen/sample g)))
what
if?
(sample-one Params param-gen)
(sample-one param-gen)

63. what
if?
(tdefn add-headers :- (merge A
{:header Headers})
[data-so-far :- [A :< AnyMap]
params])

64. what
if?
(add-headers data params)
(add-headers GroupsWithTotal data params)
(tdefn add-headers :- (merge A
{:header Headers})
[data-so-far :- [A :< AnyMap]
params])

65. Q: What could we know?
produced types
relationships between types
relationships between values

66. (defn group-up [events params]
{:post [(as-lazy-as events %)]
…))

67. relationships between types
produced types
relationships between values
data shape
data value boundaries
relationships within values

70. (def Event {:when DateTime
:what Incident
:who Customer})
(s/defn fetch-events :- [Event]
[params]
…)

71. (def Event {:when DateTime
:what Incident
:who Customer})
(s/defn fetch-events :- [t/Event]
[params]
…)
(:require
[my-project.schemas :as t])
my-project.schemas

72. implementation
schemas

73. implementation
schemas
src

74. (def params (hash-map :title gen/string-alpha-numeric
:start (datetime-before (now))
:end (datetime-before (now))))
(defspec analyze-ad-performance-spe
(for-all [events mygen/events
params mygen/params]
(analyze-ad-performance events
(:require
[my-project.gen :as mygen])
my-project.gen

75. tests
generators

76. test
tests
generators

77. test
tests
generators

78. test
tests
generators
implementation
schemas
src

79. test
tests
generators
implementation
schemas
src

80. test
tests
generators
implementation
schemas
src
src test
client

81. test
tests
generators
implementation
schemas
src
src test
client

82. implementation
schemas generators
tests

83. implementation
schemas generators
tests

84. implementation
schemas
generators
tests

85. implementation
schemas
generators
tests

86. implementation
schemas
generators
tests
src test
client

87. implementation
schemas generators
tests
src test

88. implementation
schemas
generators
tests

89. implementation
schemas
generators
tests
src test
client

90. testkit
implementation
schemas
generators
tests

91. testkit
implementation
schemas
generators
tests

92. testkit
implementation
schemas
generators
tests

93. testkit
implementation
schemas
generators
tests

95. Executable Specifications
what do we know?
how do we know it?

97. Science!
test.check
prismatic/schema
Clojure

98. Science!
generative tests
types and contracts
… your language …
Science!

99. Science!
in-memory test tools
native API definitions
… your language …
everyone!forScience!

100. Formal
Proofs
Informal
Reasoning
Experimental
Evidence

101. @jessitron
blog.jessitron.com
https://github.com/jessitron/contracts-as-types-examples
https://github.com/jessitron/slack-client
examples
resources
https://github.com/Prismatic/schema
https://github.com/miner/herbert (value relationships)
http://david-mcneil.com/post/114783282473/
extending-prismatic-schema-to-higher-order
https://github.com/jessitron/schematron
http://dl.acm.org/citation.cfm?id=2661156
Static typing and productivity: Stefik & Hanenberg 2014