Declarative Thinking and Programming

•

2 likes•827 views

Florian Wilhelm

Technology

2
! @FlorianWilhelm
" FlorianWilhelm
florianwilhelm.info
Dr. Florian Wilhelm
Data Scientist@inovex
Contributor to Pandas,
Scikit-Learn, Scipy etc.
Creator of PyScaffold

3
Outline
1. Motivation & Concept
2. Examples
3. Math Riddle

4
Motivation
House-warming
party with your
friends

6
Level of Abstraction
Right level of abstraction given a task
What is needed to describe the problem?
map & reduce

7
Imperative vs. Declarative
How vs. What
imperative declarative
over-specification,
detailed
instructions, ...
separation of
concerns, single
level of abstraction,
...
depending on the level of abstraction

8
Leaky Abstractions
Law of Leaky Abstractions by Spolsky:
“All non-trivial abstractions, to some degree, are leaky.”

9
Outline
1. Motivation & Concept
2. Examples
3. Math Riddle

10
Example 1:
List of squared number from 1 to 10
imperative:
declarative:
List Comprehensions

11
Example 2:
Dispatching with respect to some argument
Imperative:

12
Example 2: Dictionaries
Dispatching with respect to some argument
Declarative:

13
Example 3:
Find Plagiarism
How many sentences of work A are equal to my work B?
Set Theory
Sets

14
Example 4: Configuration Files
Python modules vs markup languages
YAMLvs

15
Outline
1. Motivation & Concept
2. Examples
3. Math Riddle

16Quelle: Die Zeit, Logelei 52, http://www.zeit.de/2016/52/spiele-logelei-52
Math Riddle
horizontal:
A: digit sum of horizontal C,
C: prime number,
E: palindrome,
G: multiple of the backward
number of horizontal A,
...
vertical:
All numbers are square numbers.

17
Datalog
• declarative logic programming
• subset of Prolog
• query language for deductive DBs
• other use-cases: security, data integration, information
extraction, networking, program analysis etc.
PyDatalog: https://sites.google.com/site/pydatalog/home
Features

18
PyDatalog
Rules & Facts
Read the leftmost <= as if
Is X a square number?
Is X divisible by Y?

20
PyDatalog
Rules & Facts
Map digits to number

21
Math Riddle
Keep the number of
solutions low at all times
Leaky Abstraction

22
Math Riddle
Upper left corner
A2, A3 are digits from [1...9] and number A2 A3 is prime

23http://www.florianwilhelm.info/2017/07/declarative_thinking_and_programming/
Math Riddle
Solution
Querying the knowledge base:
Solution:

25
Summary
Advantages of Declarative Programming
• improved readability of our code
• reduced number of errors
• increased performance
• separation of concerns
„Declarative programming means finding the right
abstraction level describing the problem“

26Find more details under http://florianwilhelm.info/2017/07/declarative_thinking_and_programming/
Thanks for your Attention!
Questions?

Declarative Programming is a programming paradigm that focuses on describing what should be computed in a problem domain without describing how it should be done. The talk starts by explaining differences between a declarative and imperative approach with the help of examples from everyday life. Having established a clear notion of declarative programming as well as pointed out some advantages, we transfer these concepts to programming in general. For example, the usage of control flow statements like loops over-determine the order of computation which impedes scalable execution as well as it often violates the single level of abstraction principle. Following the theoretical part of the talk, some practical examples are given how declarative programming can be applied easily within Python. This comprises the advantages and disadvantages of using a configuration file, e.g. config.yaml, versus a Python configuration module, e.g. setup.py. Furthermore, the benefits of avoiding statements of control flow with the help of list and dictionary comprehensions as well as sets are demonstrated. The talk is concluded by a short, high-level excursion to a logistic programming language, namely PyDatalog in order to build the bridge between logistic and declarative programming. This is accomplished by showing how a mathematical crossword can be easily solved with the help of declarative and logistic programming. Event: EuroPython, 13.07.2017 Speaker: Dr. Florian Wilhelm (inovex) Mehr Tech-Vorträge: https://www.inovex.de/de/content-pool/vortraege Mehr Tech-Artikel: https://www.inovex.de/blog/

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Declarative Thinking and Programming

1. Declarative Thinking & Programming Florian Wilhelm EuroPython, Rimini, 2017-07-13

2. 2 ! @FlorianWilhelm " FlorianWilhelm florianwilhelm.info Dr. Florian Wilhelm Data Scientist@inovex Contributor to Pandas, Scikit-Learn, Scipy etc. Creator of PyScaffold

3. 3 Outline 1. Motivation & Concept 2. Examples 3. Math Riddle

4. 4 Motivation House-warming party with your friends

5. 5 Motivation What is the actual task?

6. 6 Level of Abstraction Right level of abstraction given a task What is needed to describe the problem? map & reduce

7. 7 Imperative vs. Declarative How vs. What imperative declarative over-specification, detailed instructions, ... separation of concerns, single level of abstraction, ... depending on the level of abstraction

8. 8 Leaky Abstractions Law of Leaky Abstractions by Spolsky: “All non-trivial abstractions, to some degree, are leaky.”

9. 9 Outline 1. Motivation & Concept 2. Examples 3. Math Riddle

10. 10 Example 1: List of squared number from 1 to 10 imperative: declarative: List Comprehensions

11. 11 Example 2: Dispatching with respect to some argument Imperative:

12. 12 Example 2: Dictionaries Dispatching with respect to some argument Declarative:

13. 13 Example 3: Find Plagiarism How many sentences of work A are equal to my work B? Set Theory Sets

14. 14 Example 4: Configuration Files Python modules vs markup languages YAMLvs

15. 15 Outline 1. Motivation & Concept 2. Examples 3. Math Riddle

16. 16Quelle: Die Zeit, Logelei 52, http://www.zeit.de/2016/52/spiele-logelei-52 Math Riddle horizontal: A: digit sum of horizontal C, C: prime number, E: palindrome, G: multiple of the backward number of horizontal A, ... vertical: All numbers are square numbers.

17. 17 Datalog • declarative logic programming • subset of Prolog • query language for deductive DBs • other use-cases: security, data integration, information extraction, networking, program analysis etc. PyDatalog: https://sites.google.com/site/pydatalog/home Features

18. 18 PyDatalog Rules & Facts Read the leftmost <= as if Is X a square number? Is X divisible by Y?

19. 19 PyDatalog Rules & Facts Is X prime?

20. 20 PyDatalog Rules & Facts Map digits to number

21. 21 Math Riddle Keep the number of solutions low at all times Leaky Abstraction

22. 22 Math Riddle Upper left corner A2, A3 are digits from [1...9] and number A2 A3 is prime

23. 23http://www.florianwilhelm.info/2017/07/declarative_thinking_and_programming/ Math Riddle Solution Querying the knowledge base: Solution:

24. 24 Other Applications NixOS

25. 25 Summary Advantages of Declarative Programming • improved readability of our code • reduced number of errors • increased performance • separation of concerns „Declarative programming means finding the right abstraction level describing the problem“

26. 26Find more details under http://florianwilhelm.info/2017/07/declarative_thinking_and_programming/ Thanks for your Attention! Questions?

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