= Cobra Code Examples =

Some highlights of Cobra code and syntax ( on .Net).

These are selected cobra code samples for the same items as in  
[http://www.harding.edu/fmccown/vbnet_csharp_comparison.html VB and C# comparison].

== Program Structure ==

{{{
#!cobra

#use System  # already defaulted in 

namespace Hello 
	class HelloWorld 
		def main is shared
			name = "Cobra"

			args = CobraCore.commandLineArgs
			# See if an argument was passed from the command line
			# (first arg is progname)
			if args.count == 2
				name = args[1]

			Console.writeLine("Hello, " + name + "!")
			#print "Hello, [name]!"
}}}

== Comments ==
{{{
#!cobra

# Single line comment
/# Multiple
    lines  #/
    
# <summary>XML comments on single line</summary>
/# <summary>XML comments on multiple lines</summary> #/
}}}


== Data Types ==
These are as per .Net (using .Net naming rather than C#)
{{{ 
#!cobra
# Value Types
    bool
    uint8   # byte
    char
    int16, uint16, int, uint, int64, uint64        # short, ushort, int, uint, long, ulong
    float, float32, float64     #float, double
    Decimal
    DateTime   #(not a built-in C# type)
    Struct
    Enum (enumerations)

#Reference Types
    Object
    String
    arrays
    Sigs/Delegates

#Initializing  ( the explicit typing (clause 'as ????' ) is optional, types are inferred from initialisation)
		correct as bool = true
		b as uint8 = 0x2A   # hex
		person as Object? = nil
		name as String = "Dwight"
		grade as char = c'B'
		today as DateTime= DateTime.parse("12/31/2010 12:15:00 PM")
		amount as decimal = 35.99 
		gpa as float = 2.9f
		pi as float64 = 3.14159265_f64
		lTotal as int64 = 123456_i64
		sTotal as int16  = 123
		usTotal as uint16 = 123
		uiTotal as uint  = 123   # or 123u
		ulTotal as uint64 = 123   # or 123u64

		#Nilable Types
		x as int? = nil

#Anonymous Types
# Havent worked out how Cobra handle these examples yet...
#var stu = new {Name = "Sue", Gpa = 3.5}
#var stu2 = new {Name = "Bob", Gpa = 2.9}   # no Key equivalent

#Implicitly Typed Local Variables
		s = "Hello!"
		nums = @[ 1, 2, 3 ] #init from array literal
		hero = SuperHero("Batman")

#Type Information
		x as int? = 0  # Nilable int
		Console.writeLine(x.getType)        # Prints System.Int32
		Console.writeLine(sharp'typeof(int)')      # Prints System.Int32
		Console.writeLine(x.getType.name)   # prints Int32

#Type Conversion / Casting
		d = 3.5f
		i = Convert.toInt32(d)     # Set to 4 (rounds)
		i1 as int = d to int       # set to 3 (truncates decimal)	

}}}

== Constants ==
{{{ 
#!cobra
const MAX_STUDENTS as int = 25

# Can set to a const or var; may be initialized in a constructor
var MIN_DIAMETER as float is readonly= 4.93f 
}}}


== Enumerations ==
{{{
#!cobra
enum Action 
    Start, Stop, Rewind, Forward

enum Status 
    Flunk = 50
    Pass = 70 
    Excel = 90

a = Action.Stop
if a <> Action.Start
    Console.WriteLine(a + " is " + (int) a);    # Prints "Stop is 1"

Console.writeLine(Status.Pass to int) # Prints 70
Console.writeLine(Status.Pass)        # Prints Pass
}}}

== Operators ==
{{{
#!cobra

#Comparison
==  <  >  <=  >=  <>

# Arithmetic
+  -  *  /
%  (mod)
/  (integer division if both operands are ints)
Math.Pow(x, y)

#Assignment
=  +=  -=  *=  /=   %=  &=  |=  ^=  <<=  >>= 
# +=1  -=1  # ++, -- No post increment/decrement

#Bitwise
&   |   ^   ~   <<   >>

#Logical
and   or  not 
#Note: and and or perform short-circuit logical evaluations

#String Concatenation
+

}}}

== Choices ==
{{{
#!cobra

# Nil-coalescing operator
x = y ? 5   # if y != null then x = y, else x = 5

# non nil coalescing
x = y ! y.parseIt   # if y nil x = nil else x = y.parseIt()

# Ternary/Conditional operator
greeting = if(age < 20, "What's up?", "Hello")

if age < 20
    greeting = "What's up?"
else
    greeting = "Hello"

# Multiple statements must be indented following
if x <> 100 and y < 5
    x *= 5
    y *= 2


# braces not needed around condition expressions unless complicated
if x > 5
    x *= y
else if x == 5 or y % 2 == 0
    x += y
else if x < 10
    x -= y
else
     x /= y

# alternatively (1 liners)
if x > 5, x *= y
else if x == 5 or y % 2 == 0, x += y
else if x < 10, x -= y
else, x /= y

# indented action blocks, breaks not needed
case color  #   Must be integer, character, enumeration or string
  on "pink" or "red" #constants
    r++ 
  on "blue"
    b++
  on "green"
    g++ 
  else
    other++        

# 1 liners
case color                     
  on 'pink' or  'red', r++ 
  on 'blue',  b++
  on 'green', g++ 
  else,    other++        
}}}

== Loops ==
{{{
#!cobra
# re-test Loops:  

# no "until" keyword
while c < 10
    c += 1


for c in 2 : 11 : 2  # start: stop : step
    Console.writeLine(c)
    #print c

#Post-test Loop:
post while c < 10
    c += 1


# Array or collection looping
names = {"Fred", "Sue", "Barney"}
for s in names
    Console.writeLine(s)
    # print s


# Breaking out of loops
i = 0
while true
    if i == 5
        break
    i += 1

# Continue to next iteration
for i in 0 : 5 
    if i < 4
        continue
    print i       #same as Console.writeLine(i)   # Only prints 4
  
}}} 


== Arrays ==

#Preference is for (typed) collections rather than arrays

{{{
#!cobra
nums as int[] = @[1, 2, 3]
for  i in 0 : nums.length
  Console.writeLine(nums[i])


# 5 is the size of the array
names as String[]= String[](5)
names[0] = 'David';
names[5] = "Bobby";   # Throws System.IndexOutOfRangeException

# Add two elements, keeping the existing values
Array.resize(ref names, 7)

# multi dim and jagged arrays not well supported (use Collections)
twoD = sharp'new float[rows, cols]'
twoD[2,0] = 4.5f 

jagged as int[][] = sharp'new int[3][] { new int[5], new int[2], new int[3] }'
jagged[0][4] = 5 
}}}

As a collection

{{{
#!cobra
nums = [1, 2, 3]
for i in 0 : nums.count
  print nums[i]

# 5 is the size of the array
names = List(5)
names[0] = "David";
names[5] = "Bobby";   # Throws System.IndexOutOfRangeException

}}}

== Functions ==
{{{
#!cobra

	# Pass by value (in, default), in/out reference (inout), and reference (out)
	def testFunc(x as int, y as inout int, z as out int)
		x += 1  
		y += 1
		z = 5

	# Accept variable number of arguments
	def sum(nums as vari int) as int
		sum as int = 0
		for i in nums
			sum += i
		return sum
	
	def sayHello(name as String, prefix = "")
		Console.writeLine("Greetings, " + prefix + " " + name)

	def main
	
		a = 1
		b = 1 
		c as int  # c doesn't need initializing
		.testFunc(a, inout b, out c)
		Console.writeLine("{0} {1} {2}", a, b, c)  # 1 2 5
                assert c == 5 and b == 2

		total = .sum(4, 3, 2, 1)   # returns 10
		assert total == 10
		
		
		.sayHello("Strangelove", "Dr.")
		.sayHello("Mom") 
}}}


== Strings ==
{{{
#!cobra

# Escape sequences
# \r    # carriage-return
# \n    # line-feed
# \t    # tab
# \\    # backslash

# Can use either " or ' to delimit String literals
# preference is for ' unless string contains ', then use "

# String concatenation
school = "Harding\t"
school = school + "University"   # school is "Harding (tab) University"
school += "University"   # Same thing
school += 'University'   # Same thing

# Chars
letter = school[0]              # letter is H
letter = 'Z'                    # letter is Z
letter = Convert.toChar(65)     # letter is A
letter = 65 to Char             # same thing
word = school.toCharArray       # word holds Harding

# String literal
string filename = r'c:\temp\x.dat'   # Same as "c:\\temp\\x.dat"

# String comparison
mascot = 'Bisons' # or mascot = "Bisons"
if mascot == "Bisons"    # true
if mascot.equals('Bisons')   # true
if mascot.toUpper.equals('BISONS')   # true
if mascot.compareTo('Bisons') == 0  # true

# String matching - No Like equivalent, use Regex


# Substring
s = mascot.substring(2, 3)     # s is "son"

# Replacement
s = mascot.replace('sons', 'nomial')     # s is "Binomial"

# Split
names = 'Michael,Dwight,Jim,Pam'
parts = names.split(','.toCharArray())   # One name in each slot
#or
parts = names.split([ c',']) 

# Date to string
DateTime dt = DateTime(1973, 10, 12)
s = dt.toString('MMM dd, yyyy')     # Oct 12, 1973

# int to string
x = 2
y = x.toString()     # y is "2"
# string to int
x = Convert.toInt32('-5')     # x is -5

# Mutable string
buffer = System.Text.StringBuilder('two ')
buffer.append('three ')
buffer.insert(0, 'one ')
buffer.replace('two', 'TWO')
Console.writeLine(buffer)     # Prints "one TWO three"

}}}


== Regular Expressions ==
{{{
#!cobra
use System.Text.RegularExpressions


		# Match a string pattern
		r = Regex(r'j[aeiou]h?. \d:*', RegexOptions.IgnoreCase | RegexOptions.Compiled)
		if r.match('John 3:16').success   # true
			Console.writeLine("Match")


		# Find and remember all matching patterns
		s = 'My number is 305-1881, not 305-1818.'
		r = Regex(r'(\\d+-\\d+)')
		# Matches 305-1881 and 305-1818
		m as Match = r.match(s) 
		while m.success 
			#Console.writeLine("Found number: " + m.groups[1].toString + " at position " + m.groups[1].index.toString)
			print 'Found number: [m.groups[1]] at position [m.groups[1].index]'
			m = m.nextMatch to !


		# Remember multiple parts of matched pattern
		r = Regex(r'(\d\d):(\d\d) (am|pm)')
		m = r.match("We left at 03:15 pm.")
		if m.success
			Console.writeLine("Hour: " + m.groups[1].toString)       # 03
			Console.writeLine("Min: "  + m.groups[2].toString)       # 15
			Console.writeLine("Ending: " + m.groups[3].toString)   # pm

		# Replace all occurrances of a pattern
		r = Regex(r'h\\w+?d', RegexOptions.IgnoreCase)
		s = r.replace("I heard this was HARD!", "easy")   # I easy this was easy!

		# Replace matched patterns
		s = Regex.replace('123 < 456', r'(\d+) . (\d+)', '$2 > $1')   # 456 > 123

		# Split a string based on a pattern
		names = 'Michael, Dwight, Jim, Pam'
		r = Regex(r',\s*')
		parts = r.split(names)   # One name in each slot 

}}}

== Exceptions ==
{{{
#!cobra

# Throw an exception
up = Exception('Something is really wrong.')
throw up  # ha ha

# Catch an exception
try  
    y = 0
    x = 10 / y
catch ex as Exception    # Argument is optional, no "When" keyword 
    Console.writeLine(ex.message)
finally 
     Microsoft.VisualBasic.Interaction.beep
 
}}}

== Namespaces ==

{{{
#!cobra

namespace Harding.Compsci.Graphics
  ...

# or

namespace Harding 
    namespace Compsci 
        namespace Graphics
      ...

use Harding.Compsci.Graphics 
}}}

== Classes and Interfaces ==
{{{
#!cobra

## Access Modifiers
    public  # default
    private
    internal
    protected
    protected internal

#Class Modifiers
    abstract
    shared

#Method Modifiers
    abstract
    shared
    virtual #default

#No Module equivalent - just use static class

# Partial classes
class Competition is partial
  ...

# Inheritance
class FootballGame inherits Competition 
  ...


# Interface definition
interface IAlarmClock 
  def ring  # public returns void by default
  pro currentDateTime as DateTime from var
}

# Extending an interface 
interface IAlarmClock inherits IClock 
  ...
}


# Interface implementation
class WristWatch implements IAlarmClock, ITimer 

    def ring
        Console.writeLine('Wake up!')

  pro triggerDateTime as DateTime from var
  ...
}}}

== Constructors and Destructors ==
{{{
#!cobra

class SuperHero inherits Person 

    var powerLevel as int is private
    var name as String is private


    # Default constructor
    cue init 
        .powerLevel = 0
        .name = 'Super Bison'

    cue init(powerLevel as int)
        base.init('Super Bison')   # Call other constructor
        .powerLevel = powerLevel 

    cue init(name as String)
        base.init(name)      # Call base classes' constructor
        .name = name

    cue init is shared
        # Static constructor invoked before 1st instance is created

    cue finalize
        # Destructor implicitly creates a Finalize method
}}}

== Using Objects ==
{{{
#!cobra

hero as SuperHero? = SuperHero()

# No "With" but can use property initializers
hero = SuperHero(name = "SpamMan", powerLevel = 3) 

hero.defend("Laura Jones")
SuperHero.rest   # Calling static method


hero2 = hero   # Both reference the same object
hero2.name = 'WormWoman'
Console.writeLine(hero.name)   # Prints WormWoman

hero = nil    # Free the object

if hero == nil # or    if not hero
    hero = SuperHero()

obj as Object = SuperHero() 
if obj inherits SuperHero
    Console.writeLine("Is a SuperHero object.")

# Mark object for quick disposal
using reader as StreamReader = File.openText("test.txt") 
  line as String?
  while (line = reader.readLine) <> nil
    Console.writeLine(line)

}}}

== Structs ==
{{{
#!cobra
struct Student 
    var name as String
    var gpa as float

    cue init(name as String, gpa as float)
        .name = name
        .gpa = gpa

stu = Student("Bob", 3.5f)
stu2 = stu  

stu2.name = "Sue"
Console.writeLine(stu.name)    # Prints Bob
Console.writeLine(stu2.name)   # Prints Sue
}}}


== Properties ==
{{{
#!cobra


# Auto-implemented properties
pro name as String from var
get size as int from var #   Set default value in constructor

# Traditional property implementation
var name as String is private # private backing variable
#or
#var __name as String #private
#var _name as String  #protected


pro Name as String
    get 
        return .name
        # return __name
    set
        .name = value
        #__name =value

# Read-only property
var powerLevel as int is private # private backing variable
get powerlevel from var

#alternatively 
var __powerLevel = 0 # inferred as type int, private
get powerlevel from var

# Write-only property
var height as double is private # private backing variable
set height as double
    .height = if(value < 0,  0, value)

}}}

== Generics ==
{{{
#!cobra
# Enforce accepted data type at compile-time
numbers = List<of int>()
numbers.add(2)
numbers.add(4)
.displayList<of int>(numbers)

# Function can display any type of List
def displayList<of T>(List<of T> list)
    for item as T in list
        Console.writeLine(item)

# Class works on any data type
class SillyList<of T> 
    list as T[] = T[](10)
    rand as Random = Random()

    public void add(item as T)
        list[rand.next(10)] = item

    public getItem as T
        return list[rand.next(10)]
}

# Limit T to only types that implement IComparable
def maximum<of T>(items as vari T) where T must be IComparable<of T> 
    max as T = items[0]
    for item in items
        if item.compareTo(max) > 0
            max = item
    return max
}}}

== Delegates and Lambda Expresssions ==
{{{
#!cobra
sig HelloDelegate(s as String) # returns void

def sayHello(s as String) 
    Console.writeLine('Hello, ' + s)

# C# 1.0 delegate syntax with named method
hello as HelloDelegate = ref .sayHello
hello('World')   # Or hello.Invoke('World')

# C# 2.0 delegate syntax with anonymous method
# method body indented on lines following do(args)
hello2 as HelloDelegate = do(s as String)
    Console.WriteLine('Hello, ' + s)

hello2("World")

# C# 3.0 delegate syntax with lambda expression
HelloDelegate hello3 as HelloDelegate = do(s as string)=Console.writeLine('Hello, ' + s) 
hello3("World")

# Use Func<in T, out TResult> delegate to call Uppercase
convert as Func<of String, of String> = ref .uppercase
Console.writeLine(convert("test"))

def uppercase(s as String)
  return s.toUpper

# Declare and invoke Func using a lambda expression
Console.WriteLine( Func<of int, of int>do(num as int) = num + 1)(2))

# Pass lamba expression as an argument
TestValues(do(x, y) = x % y == 0)

void TestValues(Func<of int, of int, of bool> f)
  if f(8, 4)
    Console.writeLine("true")
  else
    Console.writeLine("false")

}}}


== Events ==
{{{
#!cobra
sig MsgArrivedEventHandler(message as String)

event MsgArrivedEvent as MsgArrivedEventHandler 


# listen EVENT_NAME, METHOD_NAME
listen MsgArrivedEvent, MsgArrivedEventHandler(.my_MsgArrivedEventCallback)
raise MsgArrivedEvent, "Test message"    # Throws exception if obj is null
#ignore EVENT_NAME, METHOD_NAME
ignore MsgArrivedEvent, MsgArrivedEventHandler(.my_MsgArrivedEventCallback)


using System.Windows.Forms

myButton = Button() 
listen myButton.click, System.EventHandler(ref .myButton_Click)

def myButton_Click(sender as Object, e as System.EventArgs )
    MessageBox.show(this, "Button was clicked", "Info",
        MessageBoxButtons.OK, MessageBoxIcon.Information)

}}}

== LINQ ==
 TBI
{{{
#!cobra
}}}

== Attributes ==
{{{
#!cobra
# Attribute can be applied to anything
class IsTestedAttribute inherits Attribute
    pass
    
# Attribute can only be applied to classes or structs
class AuthorAttribute inherits Attribute 
    has AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct)

    pro name as String from var
    pro version as int from var

    cue init(name as String )
        .name = name;
        .version = 0;

class Shape 
    has Author("Sue", version = 3)

    def move 
        has IsTested 
        # Do something...
    
}}}


== Console I/O ==
{{{
#!cobra
    
Console.write("What's your name? ")
name as String = Console.readLine
Console.write('How old are you? ')
age as int = Convert.toInt32(Console.readLine)
Console.writeLine("{0} is {1} years old.", name, age)
# or
Console.writeLine(name + " is " + age + " years old.")

c as int = Console.read  # Read single char
Console.writeLine(c)    # Prints 65 if user enters "A"

# alternatively

print "What's your name? " stop
name = Console.readLine
print 'How old are you? ' stop
age  = Convert.toInt32(Console.readLine)
print '[name] is [age] years old.'
# or
print String.format('{0} is {1} years old.', name, age)

c as int = Console.read  # Read single char
print c                  # Prints 65 if user enters "A"
}}}

== File I/O ==
{{{
#!cobra
#use System.IO # already autoloaded

# Write out to text file
writer as StreamWriter  = File.createText(r'c:\myfile.txt')
writer.writeLine('Out to file.')
writer.close

# Read all lines from text file
reader as StreamReader  = File.openText(r'c:\myfile.txt')
line = reader.readLine
while line 
    Console.writeLine(line)
    line = reader.readLine
reader.close

# Write out to binary file
str as String = "Text data"
num = 123
binWriter = BinaryWriter(File.openWrite(r'c:\myfile.dat'))
binWriter.write(str)
binWriter.write(num)
binWriter.close

# Read from binary file
binReader = BinaryReader(File.openRead(r'c:\myfile.dat'))
str = binReader.readString
num = binReader.readInt32
binReader.close
}}}


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