1. In search of good design...
// When I wrote this code, only God and I understood what I was doing
// Now, God only knows
Monday, October 8, 12

2. ABOUT ME
TWITTER.COM/FAUST45
GITHUB.COM/FAUST45
Monday, October 8, 12

3. What is programing about?
Goal of program convert input to reasonable output.
We calculate something and storing temp results in
vars, until we can produce complete result.
Monday, October 8, 12

4. What is programing about?
temp temp complete
results results result
Calculates Calculates Calculates
Monday, October 8, 12

5. What is programing about?
Program
State
temp temp complete
results results result
Calculates Calculates Calculates
Monday, October 8, 12

6. What is programing about?
Program
State
temp temp complete
results results result
Calculates Calculates Calculates
Layer control order of calculations
Monday, October 8, 12

7. What is programing about?
Program
State
temp temp complete
results results result
Layer manages access to program state
Calculates Calculates Calculates
Layer control order of calculations
Monday, October 8, 12

8. Looks simple?
Program
State
temp temp complete
results results result
Layer manages access to program state
Calculates Calculates Calculates
Layer control order of calculations
Monday, October 8, 12

9. Lets add some complexity
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10. Lets make
control order layer
hard to understand
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11. Let’s split
control order layer
and hide in Calculate units
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12. Who can help us?
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13. GOTO
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14. Lets do the same with
state manages layer
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15. Lets make
state manages layer
hard to understand
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16. Lets split
state manages layer
and hide in Calculate units
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17. Example
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18. Example
Will never
happens
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19. Happy debugging suckers
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20. Any part of the program can
rewrite state, and it's not easy to
tell where it's happening.
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21. Unit tests don’t save us
Unit test passed success.
Only when you run all program
you can touch the bug
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22. Thats most popular
programing style, for
today.
Imperative
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23. Where the answer?
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24. Functional Programming
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25. Functional model
Program
State
temp temp complete
results results result
Layer manages access to program state
Calculates Calculates Calculates
Layer control order of calculations
Monday, October 8, 12

26. You construct program
from units of pure
calculations
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27. Units of pure calculations
have no direct access to
program state
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28. You pass a pice of state in
params
function send_money(sender_account,
receiver_account,
amount_to_send)
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29. and return result of
calculations, some
new pice of state
function send_money(sender_account, ...)
return
how_sender_account_looks_after_money_was_send
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30. Calculations depends only
from params you passed,
nothing hidden
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31. Functional
Program
state
Pice of program
state
Calculate
return result
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32. Imperative
Program
state
Pice of program
dir state
ect
acc
ess
Calculate
return result
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33. Rich Hickey
Creator of clojure, language with immutable
data by default.
Dialect of Lisp on top of Java Virtual Machine
He was inspired by paper “Out of the Tar Pit”
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34. Model where you don’t
rewrite values but
produce new values
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35. Clojure introduce fast
immutable data
structures
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36. Implemented with
Binary trees
and
structure sharing
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37. Monday, October 8, 12

38. Mutable data
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39. Resources
★ “Out of the Tar Pit”
★ “The Art of Unix Programming”
★ “Functional programming is a ghetto” (blog bost by
Michael O.Church)
★ Rich Hickey videos
★ Stuart Holloway videos - “Simplicity Ain't Easy”
Monday, October 8, 12