[odin/en] Add Odin.md (#5346)

* Create odin.md

* Add link to Odin book

* Improve build-int data structure section

* Fix os.open() example and remove SIMD

odin.md

@@ -0,0 +1,575 @@
+---
+name: Odin
+contributors:
+    - ["Collin MacDonald", "https://github.com/CollinEMac"]
+filename: learnodin.odin
+---
+
+Odin was created by Bill "gingerBill" Hall. It is a general-purpose systems
+programming language that emphasizes simplicity, readability, and performance
+without garbage collection. Odin bills itself as "the C alternative for the
+joy of programming."
+
+```odin
+// Single line comments start with two slashes.
+
+/*
+   Multiline comments start with slash-star,
+   and end with star-slash. They can be nested!
+   /*
+       Like this!
+   */
+*/
+
+// This is the classic "hello world" program in Odin.
+package main
+
+import "core:fmt"
+
+main :: proc() {
+    fmt.println("Hellope!")
+}
+
+////////////////////////////////////////////////////
+## 1. Basic Data Types and Operators
+////////////////////////////////////////////////////
+
+// Integers - Odin has explicit sized integer types
+x: i32 = 42          // 32-bit signed integer
+y: u64 = 100         // 64-bit unsigned integer
+z: int = 123         // Platform-dependent integer (usually i64)
+
+// You can use underscores for readability in numbers
+big_number := 1_000_000
+
+// Floating point numbers
+pi: f32 = 3.14159    // 32-bit float
+e: f64 = 2.71828     // 64-bit float (default for float literals)
+
+// Boolean
+is_true: bool = true
+is_false: bool = false
+
+// Rune (Unicode character)
+letter: rune = 'A'
+emoji: rune = '🚀'
+
+// Strings
+name: string = "Odin Programming"
+raw_string := `C:\Windows\System32`  // Raw string with backticks
+
+// String length (in bytes, not characters!)
+length := len(name)
+
+// Arithmetic operators work as you'd expect
+result := 10 + 5    // 15
+diff := 10 - 5      // 5
+product := 10 * 5   // 50
+quotient := 10 / 5  // 2
+remainder := 10 % 3 // 1
+
+// Comparison operators
+is_equal := 10 == 10        // true
+not_equal := 10 != 5        // true
+greater := 10 > 5           // true
+less_equal := 5 <= 10       // true
+
+// Logical operators
+and_result := true && false  // false
+or_result := true || false   // true
+not_result := !true          // false
+
+// Bitwise operators
+bit_and := 0b1010 & 0b1100   // 0b1000
+bit_or := 0b1010 | 0b1100    // 0b1110
+bit_xor := 0b1010 ~ 0b1100   // 0b0110 (note: ~ is XOR in Odin)
+bit_not := ~0b1010           // bitwise NOT
+
+////////////////////////////////////////////////////
+## 2. Variables and Constants
+////////////////////////////////////////////////////
+
+// Variable declaration with type inference
+some_number := 42            // Type inferred as int
+some_text := "Hello"         // Type inferred as string
+
+// Explicit type declaration
+explicit_int: int = 42
+explicit_float: f64 = 3.14
+
+// Uninitialized variables are zero-initialized
+uninitialized_int: int       // Defaults to 0
+uninitialized_bool: bool     // Defaults to false
+uninitialized_string: string // Defaults to ""
+
+// Constants are defined with ::
+PI :: 3.14159
+MESSAGE :: "This is a constant"
+
+// Typed constants
+TYPED_CONSTANT : f32 : 2.71828
+
+// Multiple assignment
+a, b := 10, 20
+a, b = b, a  // Swap values
+
+////////////////////////////////////////////////////
+## 3. Arrays and Slices
+////////////////////////////////////////////////////
+
+// Fixed-size arrays
+numbers: [5]int = {1, 2, 3, 4, 5}
+chars: [3]rune = {'A', 'B', 'C'}
+
+// Array with inferred size
+inferred := [..]int{10, 20, 30, 40}
+
+// Zero-initialized array
+zeros: [10]int  // All elements are 0
+
+// Accessing array elements
+first := numbers[0]     // 1
+last := numbers[4]      // 5
+array_length := len(numbers)  // 5
+
+// Slices - dynamic views into arrays
+slice: []int = {1, 2, 3, 4, 5}  // Slice literal
+array_slice := numbers[1:4]     // Slice of array from index 1 to 3
+full_slice := numbers[:]        // Slice of entire array
+
+// Dynamic arrays - can grow and shrink
+dynamic_array: [dynamic]int
+append(&dynamic_array, 1)
+append(&dynamic_array, 2, 3, 4)  // Append multiple elements
+
+// Remember to clean up dynamic arrays
+defer delete(dynamic_array)
+
+////////////////////////////////////////////////////
+## 4. Control Flow
+////////////////////////////////////////////////////
+
+// If statements
+age := 25
+if age >= 18 {
+    fmt.println("Adult")
+} else if age >= 13 {
+    fmt.println("Teenager")
+} else {
+    fmt.println("Child")
+}
+
+// For loops - Odin's only loop construct
+// C-style for loop
+for i := 0; i < 10; i += 1 {
+    fmt.println(i)
+}
+
+// While-style loop
+counter := 0
+for counter < 5 {
+    fmt.println(counter)
+    counter += 1
+}
+
+// Infinite loop
+for {
+    // This runs forever (until break)
+    break  // Exit the loop
+}
+
+// Iterating over arrays/slices with index
+numbers_array := [3]int{10, 20, 30}
+for value, index in numbers_array {
+    fmt.printf("Index %d: Value %d\n", index, value)
+}
+
+// Iterating over just values
+for value in numbers_array {
+    fmt.println(value)
+}
+
+// Switch statements
+day := "Monday"
+switch day {
+case "Monday", "Tuesday", "Wednesday", "Thursday", "Friday":
+    fmt.println("Weekday")
+case "Saturday", "Sunday":
+    fmt.println("Weekend")
+case:  // Default case
+    fmt.println("Unknown day")
+}
+
+// Switch with no condition (like if-else chain)
+switch {
+case age < 13:
+    fmt.println("Child")
+case age < 20:
+    fmt.println("Teenager")
+case:
+    fmt.println("Adult")
+}
+
+////////////////////////////////////////////////////
+## 5. Procedures (Functions)
+////////////////////////////////////////////////////
+
+// Basic procedure definition
+add :: proc(a: int, b: int) -> int {
+    return a + b
+}
+
+// Procedure with multiple return values
+divide :: proc(a: int, b: int) -> (int, bool) {
+    if b == 0 {
+        return 0, false  // Division by zero
+    }
+    return a / b, true
+}
+
+// Using the procedure
+sum := add(5, 3)                    // 8
+quotient, ok := divide(10, 2)       // 5, true
+quotient_bad, ok_bad := divide(10, 0) // 0, false
+
+// Procedure with default parameters (using overloading)
+greet :: proc(name: string) {
+    fmt.printf("Hello, %s!\n", name)
+}
+
+greet :: proc() {
+    greet("World")
+}
+
+// Variadic procedures (variable number of arguments)
+sum_all :: proc(numbers: ..int) -> int {
+    total := 0
+    for number in numbers {
+        total += number
+    }
+    return total
+}
+
+result_sum := sum_all(1, 2, 3, 4, 5)  // 15
+
+////////////////////////////////////////////////////
+## 6. Structs
+////////////////////////////////////////////////////
+
+// Struct definition
+Person :: struct {
+    name: string,
+    age:  int,
+    height: f32,
+}
+
+// Creating struct instances
+person1 := Person{
+    name = "Alice",
+    age = 30,
+    height = 5.6,
+}
+
+// Partial initialization (remaining fields are zero-initialized)
+person2 := Person{
+    name = "Bob",
+    // age and height default to 0
+}
+
+// Accessing struct fields
+fmt.printf("%s is %d years old\n", person1.name, person1.age)
+
+// Modifying struct fields
+person1.age = 31
+
+// Procedure that works with structs
+celebrate_birthday :: proc(person: ^Person) {  // ^ means pointer
+    person.age += 1
+    fmt.printf("Happy birthday! %s is now %d\n", person.name, person.age)
+}
+
+celebrate_birthday(&person1)  // Pass address with &
+
+////////////////////////////////////////////////////
+## 7. Enums and Unions
+////////////////////////////////////////////////////
+
+// Enums
+Color :: enum {
+    RED,
+    GREEN,
+    BLUE,
+    YELLOW,
+}
+
+my_color := Color.RED
+
+// Enums with explicit values
+Status :: enum u8 {
+    OK = 0,
+    ERROR = 1,
+    WARNING = 2,
+}
+
+// Unions (tagged unions)
+Shape :: union {
+    Circle: struct { radius: f32 },
+    Rectangle: struct { width, height: f32 },
+    Triangle: struct { base, height: f32 },
+}
+
+my_shape := Shape(Circle{{radius = 5.0}})
+
+// Pattern matching with unions
+switch shape in my_shape {
+case Circle:
+    fmt.printf("Circle with radius %.2f\n", shape.radius)
+case Rectangle:
+    fmt.printf("Rectangle %.2f x %.2f\n", shape.width, shape.height)
+case Triangle:
+    fmt.printf("Triangle base %.2f, height %.2f\n", shape.base, 
+               shape.height)
+}
+
+////////////////////////////////////////////////////
+## 8. Maps
+////////////////////////////////////////////////////
+
+// Map declaration
+scores: map[string]int
+
+// Initialize map
+scores = make(map[string]int)
+defer delete(scores)  // Clean up when done
+
+// Add key-value pairs
+scores["Alice"] = 95
+scores["Bob"] = 87
+scores["Charlie"] = 92
+
+// Access values
+alice_score := scores["Alice"]  // 95
+
+// Check if key exists
+bob_score, exists := scores["Bob"]
+if exists {
+    fmt.printf("Bob's score: %d\n", bob_score)
+}
+
+// Iterate over map
+for name, score in scores {
+    fmt.printf("%s: %d\n", name, score)
+}
+
+// Map literal
+ages := map[string]int{
+    "Alice" = 30,
+    "Bob" = 25,
+    "Charlie" = 35,
+}
+defer delete(ages)
+
+////////////////////////////////////////////////////
+## 9. Pointers and Memory Management
+////////////////////////////////////////////////////
+
+// Pointers
+number := 42
+number_ptr := &number        // Get address of number
+value := number_ptr^         // Dereference pointer (get value)
+
+fmt.printf("Value: %d, Address: %p\n", value, number_ptr)
+
+// Dynamic memory allocation
+// new() allocates and returns a pointer
+int_ptr := new(int)
+int_ptr^ = 100
+defer free(int_ptr)  // Clean up memory
+
+// make() for complex types
+my_slice := make([]int, 5)    // Slice with length 5
+defer delete(my_slice)
+
+////////////////////////////////////////////////////
+## 10. Error Handling
+////////////////////////////////////////////////////
+
+// Odin uses multiple return values for error handling
+read_file :: proc(filename: string) -> (string, bool) {
+    // Simulate file reading
+    if filename == "" {
+        return "", false  // Error case
+    }
+    return "file contents", true  // Success case
+}
+
+// Using the error-returning procedure
+content, success := read_file("myfile.txt")
+if !success {
+    fmt.println("Failed to read file")
+} else {
+    fmt.printf("File content: %s\n", content)
+}
+
+// Common pattern with or_return
+parse_number :: proc(s: string) -> (int, bool) {
+    // This is a simplified example
+    if s == "42" {
+        return 42, true
+    }
+    return 0, false
+}
+
+example_with_error_handling :: proc() -> bool {
+    // or_return automatically returns false if the second value is false
+    num := parse_number("42") or_return
+    fmt.printf("Parsed number: %d\n", num)
+    return true
+}
+
+////////////////////////////////////////////////////
+## 11. Packages and Imports
+////////////////////////////////////////////////////
+
+// Every .odin file starts with a package declaration
+// package main  // (Already declared at the top)
+
+// Import from core library
+import "core:fmt"
+import "core:strings"
+import "core:os"
+
+// Import with alias
+import str "core:strings"
+
+// Using imported procedures
+text := "Hello, World!"
+upper_text := strings.to_upper(text)
+fmt.println(upper_text)
+
+// Import from vendor packages (external libraries)
+// import "vendor:raylib"
+
+////////////////////////////////////////////////////
+## 12. Compile-time Features
+////////////////////////////////////////////////////
+
+// Compile-time conditionals
+when ODIN_OS == .Windows {
+    // Windows-specific code
+    fmt.println("Running on Windows")
+} else when ODIN_OS == .Linux {
+    // Linux-specific code
+    fmt.println("Running on Linux")
+} else {
+    // Other platforms
+    fmt.println("Running on other platform")
+}
+
+// Compile-time constants
+ODIN_DEBUG :: #config(DEBUG, false)
+
+when ODIN_DEBUG {
+    fmt.println("Debug mode enabled")
+}
+
+// Generics (Parametric polymorphism)
+Generic_Array :: struct($T: typeid) {
+    data: []T,
+}
+
+max :: proc(a: $T, b: T) -> T {
+    return a if a > b else b
+}
+
+max_int := max(10, 20)      // T becomes int
+max_float := max(3.14, 2.71) // T becomes f64
+
+////////////////////////////////////////////////////
+## 13. Built-in Data Structures
+////////////////////////////////////////////////////
+
+// Bit sets for flags
+File_Mode :: enum {
+    READ,
+    WRITE,
+    EXECUTE,
+}
+
+permissions: bit_set[File_Mode]
+permissions |= {.READ, .WRITE}        // Set multiple flags
+permissions &~= {.WRITE}              // Remove flag
+has_read := .READ in permissions      // Check flag
+is_readonly := permissions == {.READ} // Compare sets
+
+// Complex numbers
+z1 := complex64(3 + 4i)
+z2 := complex64(1 - 2i)
+sum := z1 + z2                        // (4 + 2i)
+magnitude := abs(z1)                  // 5.0
+
+// Matrices for linear algebra
+transform := matrix[3, 3]f32{
+    1, 0, 5,  // Translation X = 5
+    0, 1, 3,  // Translation Y = 3  
+    0, 0, 1,  // Homogeneous coordinate
+}
+
+point := [3]f32{10, 20, 1}
+transformed := transform * point      // Matrix multiplication
+
+// Quaternions for 3D rotations
+identity_rot := quaternion128{0, 0, 0, 1}  // No rotation
+rotation_90_z := quaternion128{0, 0, 0.707, 0.707}  // 90° around Z
+
+////////////////////////////////////////////////////
+## 14. Context System and Defer
+////////////////////////////////////////////////////
+
+// Odin has an implicit context system for threading allocators,
+// loggers, and other utilities through your program
+
+example_with_context :: proc() {
+    // Save current context
+    old_allocator := context.allocator
+    
+    // Use a different allocator temporarily
+    temp_allocator := context.temp_allocator
+    context.allocator = temp_allocator
+    
+    // All allocations in this scope use temp_allocator
+    temp_data := make([]int, 100)
+    // No need to delete temp_data - it's automatically cleaned up
+    
+    // Restore original allocator
+    context.allocator = old_allocator
+}
+
+// defer ensures cleanup happens when scope exits
+resource_management_example :: proc() {
+    file_handle := os.open("example.txt", os.O_RDONLY, 0) or_return
+    defer os.close(file_handle)  // Always closed when function exits
+    
+    buffer := make([]u8, 1024)
+    defer delete(buffer)  // Always freed when function exits
+    
+    // Use file_handle and buffer...
+    // They're automatically cleaned up even if we return early
+}
+```
+
+## Further Reading
+
+The [Odin Programming Language website](https://odin-lang.org/) provides 
+excellent documentation and examples.
+
+The [overview](https://odin-lang.org/docs/overview/) covers much of the 
+language in detail.
+
+The [GitHub examples repository](https://github.com/odin-lang/examples) 
+contains idiomatic Odin code examples.
+
+For learning resources:
+- ["Understanding the Odin Programming Language" by Karl Zylinski](https://odinbook.com)
+- [Odin Discord](https://discord.gg/sVBPHEv) for community support
+- [FAQ](https://odin-lang.org/docs/faq/) for common questions