Introduction to Gura Programming Language. This has been translated from a material written in Japanese for LL Diver event on Aug 23, 2014.

1. Introduction to Gura Programming Language
www.gura-lang.org
Copyright © 2014 ypsitau@nifty.com
LL Diver on Aug 23, 2014

2. Copyright (C) 2014 ypsitau 2/49
Author
Name Yutaka Saito
Experience Embedded Firmware to GUI
Job History Electric-app maker, chip maker, venture
Current Job Free, unemployed rather
Favorite Lang C++, Gura
devoted to Gura

3. Copyright (C) 2014 ypsitau 3/49
Extension Module
Iterator Operation
Basic Specification
What's Gura?
Agenda
What's Gura?

4. Copyright (C) 2014 ypsitau 4/49
What's Gura?
Repeat processes appear in programs so often.
for (i = 0; i < 10; i++) {
}
people.each do |person|
end
for x in range(10):
hoge
Can I deal them without verbose control sequence?

5. Copyright (C) 2014 ypsitau 5/49
Case Study (1)
Here's a number sequence: -3, -2, -1, 0, 1, 2, 3.
Make a list of squared values of them.
Think it with your
favorite language ...
x
y

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Gura's Program (1)
x = [-3, -2, -1, 0, 1, 2, 3]
y = x * x

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Gura's Program (1)
x = [-3, -2, -1, 0, 1, 2, 3]
y = x * x
Multiplying iterator is generated.
Its evaluation creates list.
Iterator Lists generate iterators.1
2
3Evaluation
List List
Iterator
Iterator
List

8. Copyright (C) 2014 ypsitau 8/49
Case Study (2)
Create a program that reads a text file and prints
its content along with line numbers.
Think it with your
favorite language …
1: #include <std
2: int main()
3: {
4: printf(“H
5: }

9. Copyright (C) 2014 ypsitau 9/49
Gura's Program (2)
printf('%d: %s',
1.., readlines('hello.c'))

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Gura's Program (2)
printf('%d: %s',
1.., readlines('hello.c'))
Iterator that executes printf
for each item is generated.
It's destroyed after evaluated.
1
2
Iterator Iterator
Iterator
Evaluation

11. Copyright (C) 2014 ypsitau 11/49
After All, Gura is ..
A language that can generate iterators
from iterators and evaluate them.
Gura calls this operation “Mapping”.
Iterator
Iterator
Iterator
Iterator
Iterator Iterator
Iterator Evaluation

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Expected Benefits
Simplifies codes of repeat process.
Facilitates parallel computing, maybe.
1
2

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Idea for Parallel Computing
Elements in iterator generated last
Iterator generation
requires less load.
Evaluation stage
needs much load.
Distributes elements
to processors
for evaluation.
Eval
Iterator
Iterator
Iterator
Iterator
Iterator Iterator
Iterator Evaluation
Eval Eval

14. Copyright (C) 2014 ypsitau 14/49
Extension Module
Iterator Operation
Basic Specification
What's Gura?
Agenda
Basic Specification

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Basic Specification
Function
Control Sequence
OOP
Collection
Scope Management

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Basic Spec (1) Function
x = f(a => 3, b => 4)
f(a:number, b:number) = {
a * a + b * b
}
x = f(3, 4)
Definition (1)
Call
Type can be specified
Named arguments

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Basic Spec(1) Function
f(3) // a=3, b=[]
f(3, 1) // a=3, b=[1]
f(3, 1, 4, 1) // a=3, b=[1,4,1]
f(a, b*) = {
// any job
}
Call
Definition (2) Variable-length argument that
takes more than 0 value.
b+ takes more than 1 value.

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Basic Spec(1) Function
my_loop(n) {block} = {
while (n > 0) {
block()
n -= 1
}
}
my_loop(3) {
println('hello')
}
Definition (3)
Call
Takes block expression as function object.
{block?} means an optional block.

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Basic Spec(2) Control Sequence
if (…) {
} elsif (…) {
} elsif (…) {
} else {
}
try {
} catch (…) {
} catch (…) {
}
for (…) {
}
repeat (…) {
}
while (…) {
}
Repeat Branch Exception
cross (…) {
}

20. Copyright (C) 2014 ypsitau 20/49
Basic Spec(3) OOP
Fruit = class {
__init__(name:string, price:number) = {
this.name = name
this.price = price
}
Print() = {
printf('%s %dn', this.name, this.price)
}
}
fruit = Fruit('Orange', 90)
fruit.Print()
Class Definition
Instantiation and Method Call
Constructor

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Basic Spec(3) OOP
A = class {
__init__(x, y) = {
// any jobs
}
}
B = class(A) {
__init__(x, y, z) = {|x, y|
// any jobs
}
}
Inheritance
Arguments for
base class constructor

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Basic Spec(4) Collection
a = [3, 1, 4, 1, 5, 9]
b = ['zero', 'one', 2, 3, 'four', 5]
c = %{ `a => 3, `b => 1, `c => 4 }
d = %{
'いぬ' => 'dog', 'ねこ' => 'cat'
}
List
Dictionary

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Basic Spec(5) Scope Management
create_counter(n:number) = {
function {
n -= 1
}
}
c = create_counter(4)
c() // returns 3
c() // returns 2
c() // returns 1
Closure
Each function has lexical scope.

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Extension Module
Iterator Operation
Basic Specification
What's Gura?
Agenda
Iterator Operation

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Iterator Operation
Implicit Mapping
Member Mapping
Function
Repeat Control
Mapping
Generation
Iterator Operation: Mapping and Generation
Iterator
Iterator
Iterator
Iterator
Iterator

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Gura's List and Iterator
List
Iterator
['apple', 'orange', 'grape']
('apple', 'orange', 'grape')
All the elements are stored in memory.
Each element would be generated.
Capable of random access
Only evaluation could make next element available

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Gura's List and Iterator
Iterator
List Evaluation
Generation

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Iterator Operation(1) Implicit Mapping
Generates iterator embedding function or operator
Function
or
Operator
argument values returned value
Implicit Mapping
Iterator
Iterator
Iterator
Iterator

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Iterator Operation(1) Implicit Mapping
f(a:number, b:number) = {
a * b
}
Usual Function
f(a:number, b:number):map = {
a * b
}
Mappable Function Specifies attribute :map

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Iterator Operation(1) Implicit Mapping
f(3, 4)Number
f([2, 3, 4], [3, 4, 5])List
f((2, 3, 4), (3, 4, 5))Iterator
f(5, (3, 4, 5))Number and
Iterator
Answer: 12
Answer: [6, 12, 20]
Answer: (6, 12, 20)
Answer: (15, 20, 25)

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Iterator Operation(1) Implicit Mapping
List
Scalar
Iterator
List
Others
Mapping process depends arguments' data type
Iterator
Categorize
data types
Three rules to apply mapping

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Iterator Operation(1) Implicit Mapping
Generates an iterator
if at least one iterator exists in arguments.
Rule 1
Iterator
Iterator
Iterator
List
Iterator
Scalar
Iterator
Iterator
Iterator

33. Copyright (C) 2014 ypsitau 33/49
Iterator Operation(1) Implicit Mapping
Generates a list if there's no iterator and
at least one list exists in arguments.
Rule 2
List
List
List
Scalar
List
List

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Iterator Operation(1) Implicit Mapping
Generates a scalar
if only scalars exist in arguments.
Rule 3
Scalar
Scalar
Scalar

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Iterator Operation(2) Member Mapping
Member Mapping
fruits[0] fruits[1] fruits[2]
name name name
Print() Print() Print()
price price price
List of instances
Generates an iterator to access instance members.

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Iterator Operation(2) Member Mapping
Member Mapping
fruits[0] fruits[1] fruits[2]
name name name
Print() Print() Print()
price price price
Iterator
Generates an iterator to access instance members.
fruits:*name
fruits:*price
fruits:*Print()
List of instances

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Iterator Operation(2) Member Mapping
sum = 0
for (fruit in fruits) {
sum += fruit.price
}
println(sum)
println(fruits:*price.sum())
Prints summation of Fruit instance's member price.Task
Solution1 Using repeat control
Using Member MappingSolution2

38. Copyright (C) 2014 ypsitau 38/49
Iterator Operation(3) Function
Function A function should return data sequence
by an iterator, not a list.
rtn = readlines('hello.c')
rtn = range(10)
Iterator to generate strings of each line
Iterator to generate numbers from 0 to 9
Design Policy
Iterator

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Iterator Operation(3) Function
rtn = readlines('hello.c'):list
rtn = range(10):list
List containing strings of each line
List containing numbers from 0 to 9
List
Call with attribute :list
in order to get a listFunction Iterator

40. Copyright (C) 2014 ypsitau 40/49
Iterator Operation(4) Repeat Control
Generate an iterator
from repeat control
Repeat Control
values
repeating job
x = for (…):iter {
}
Evaluation result of
repeating job comes to be
the iterator's element
Specify attribute :iter
for
repeat
while
cross
Iterator

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Iterator Operation(4) Repeat Control
n = 0
x = for (i in 0..5):iter {
n += i
}
Nothing happens at this time
println(x)
Prints result: 0 1 3 6 10 15
Example of repeat control iterator

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Iterator Operation(4) Repeat Control
prime() = {
p = []
for (n in 2..):xiter {
if (!(n % p.each() == 0).or()) {
p.add(n)
n
}
}
}
primes = prime()
Iterator to generate numbers (2, 3, 5, 7..)
Iterator to generate prime numbers

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Extension Module
Iterator Operation
Basic Specification
What's Gura?
Agenda
Extension Module

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Extension Module
Design Policy
Gura Interpreter itself should have as little dependency
on OS-specific functions and libraries as possible.
It should extend capabilities by importing modules.
Gura Interpreter
Module
ModuleModule
Module
Module
Module

45. Copyright (C) 2014 ypsitau 45/49
Bundled Modules
GUI
wxWidgets Tk SDL
Graphic Drawing
Cairo OpenGL FreeType
Image Data
JPEG PNG GIF BMP
ICO XPM PPM TIFF
Network
cURL Server
Text Processing
Regular Exp
yamlXMLCSV
markdown
Archive and Compression
TAR ZIP GZIP BZIP

46. Copyright (C) 2014 ypsitau 46/49
Cooperation between Modules
Gura Interpreter
JPEG PNG GIF BMP ICO XPM PPM TIFF
Cairo OpenGL FreeType wxWidgets Tk SDL
image
Graphic Drawing
Display Output
Read/Write of Image Data

47. Copyright (C) 2014 ypsitau 47/49
Application Example
[ ID Photo Made at Home - Gura Shot ]
Creates ID photos by extracted face
image from a file of digital camera.
Outputs results in PDF and JPEG.
JPEG image Cairo image JPEG
wxWidgets
Reading File Composing Image Writing File
Output to Display

48. Copyright (C) 2014 ypsitau 48/49
Thank you
www.gura-lang.org