C has become pretty old school, but the way C developers now and throughout its history have used C, extended C is the foundation of a amazing dynamic languages. This talk describes some dynamic C data structures and also gives an overview of developing a language on top of these tools.

1. What the
C?
Kane Baccigalupi
@rubyghetto

2. What the
C?
What can you do with it, nowadays?

3. C
1998
Coolest Hottest Language was ….
Java
but learning C was like learning ABCs

4. C
1998
Coolest Hottest Language was ….
Java
but learning C was like learning ABCs
And not very hip companies were making websites in it.
Really!

5. Assembly
C stands on the shoulders
of giants (who were women!)

6. C
today
what is done with it

7. C
today
what is done with it
utilities
git, bash, diff …

8. C
today
what is done with it
utilities
git, bash, diff …
language extensions: JSON, ruby => nokogiri

9. C
today
what is done with it
utilities
git, bash, diff …
language extensions: JSON, ruby => nokogiri
languages!

10. Dynamic Languages in
CExtends what C programmers have always done
Bend the mind
Allow unknowns at Runtime
to be compiled into extensible ideas

11. C Building Blocks
Arrays
int counts[3];
char string[6];

12. C Building Blocks
int counts[3];
char string[6];
Limitations:
• variables can’t be asked about size
• variables can’t be asked about type
• variables can’t be increased
by just adding values beyond declaration

13. C Building Blocks
typedef struct Array {
int length;
int capacity;
void **values;
} Array;

14. C Building Blocks
typedef struct Array {
int length;
int capacity;
void **values;
} Array;

15. C Building Blocks
[ _ ]
Dynamic Array
capacity: 4
length: 3
values:

16. C Building Blocks
[ _ _ ]
Dynamic Array: pop
capacity: 4
length: 2
values:

17. C Building Blocks
[ _ ]
Dynamic Array: push
capacity: 4
length: 4
values:

18. C Building Blocks
[ _ … ]
Dynamic Array: push
capacity: 16
length: 5
values:
reallocation

19. C Building Blocks
[ _ ]
Dynamic Array: shift?
capacity: 4
length: 2
values:
not efficient!

20. C Building Blocks
Dynamic Array:
Limitation:
• shift/unshift operations costly
• insert in middle inefficient
Benefit:
• efficient modification to end
• easy value extraction from an index
• easy value addition at a particular index

21. C Building Blocks
Linked Lists:
typedef struct List {
int length;
struct Node *first;
struct Node *last;
} List;
typedef struct Node {
void *value;
struct Node *prev;
struct Node *next;
} Node;

22. C Building Blocks
Linked Lists (double):
length: 4
first:
last:

23. C Building Blocks
Linked Lists (double):
Limitation:
• can’t easily traverse to particular index
Benefits:
• insert anywhere
• easy add to beginning

24. C Building Blocks
Trees:
length: 4
root:

25. C Building Blocks
Hash (combining lots):
// javascript
obj = {“hello”: “world”};
obj[‘hello’] // returns “world”
Also called dictionary & map

26. C Building Blocks
Hash (combining lots):
length: 4
capacity: 5
values:
[ ]
dynamic array
of
dynamic arrays

27. C Building Blocks
Given: string key & value to set
[ ]
dynamic array
of
dynamic arrays
• key converted to hash (long int)
• take modulo of hash to find a bucket
(top level location)
• node has ref to
• original key
• and hash
• and value
• node is shoved into bucket

28. Now that we have
Building Blocks,
let’s build a
language!

29. How to make a
language
1. Lex: convert string to tokens
2. Parse: build a syntax tree from tokens
3. Interpret: evaluate the syntax tree

30. Lexing
Conversion: 1d array to 1d array
1 + x
<integer 1> <id ‘+’> <integer 1>

31. Parsing
Converting 1d array into a tree
<integer 1> <id ‘+’> <id ‘x’>
(method_call,
(receiver, (literal, <integer 1>)),
(message, (lookup, <id ‘+’>)),
(arguments, (lookup, <id ‘x’>))
)

32. Lexing & Parsing
There is a better way!

33. Interpretatio
n
Taking the tree expression
and executing it as code!
(method_call,
(receiver, (literal, <integer 1>)),
(message, (lookup, <id ‘+’>)),
(arguments, (lookup, <id ‘x’>))
)
• Find or build literal integer `1`
• Use Integer class to lookup `+`
method
• lookup in nested contexts id `x`
• Call `+` method on integer object
`1` with lookup value of x as
argument

34. FAUXY!
Watch it happen:
github.com/baccigalupi/fauxy

35. FAUXY!
Faux Objects
Faux Functional
Concurrent
Dynamic
Statically typed and immutable!
with Pattern Matching/Multiple Dispatch

36. FAUXY!
Faux Objects
Faux Functional
Concurrent
Dynamic
Statically typed and immutable!
with Pattern Matching/Multiple Dispatch
NumberToWords.Digit: Class.new(n) -> {
to-words: -> { convert(n) }
convert: -> (n: 1) { 'one' }
convert: -> (n: 2) { 'two' }
convert: -> (n: 3) { 'three' }
convert: -> (n: 4) { 'four' }
convert: -> (n: 5) { 'five' }
convert: -> (n: 6) { 'six' }
convert: -> (n: 7) { 'seven' }
convert: -> (n: 8) { 'eight' }
convert: -> (n: 9) { 'nine' }
}

37. Attribution
• Assembly Example: homepage.cs.uri.edu
• Women using punchcards: en.wikipedia.org

38. ME!
Kane Baccigalupi
@baccigalupi
Ruby/Rails/JS
Rescue Coding