mojo-syntax

def compute(x: Int) -> Int:              # non-raising (compiler enforced)
    return x * 2

def load(path: String) raises -> String: # explicitly raising
    return open(path).read()

def main() raises:                       # main usually raises → def raises
    ...

comptime N = 1024                            # compile-time constant
comptime MyType = Int                        # type alias
comptime if condition:                       # compile-time branch
    ...
comptime for i in range(10):                 # compile-time loop
    ...
comptime assert N > 0, "N must be positive"  # compile-time assertion

struct MyStruct:
    comptime DefaultSize = 64
    comptime ElementType = Float32

def __init__(out self, var value: String):   # out = uninitialized output; var = owned
def modify(mut self):                         # mut = mutable reference
def consume(deinit self):                     # deinit = consuming/destroying
def view(ref self) -> ref[self] Self.T:       # ref = reference with origin
def view2[origin: Origin, //](ref[origin] self) -> ...:           # ref[origin] = explicit origin

# Constructor
def __init__(out self, x: Int):
    self.x = x

# Copy constructor (keyword-only `copy` arg)
def __init__(out self, *, copy: Self):
    self.data = copy.data

# Move constructor (keyword-only `deinit take` arg)
def __init__(out self, *, deinit take: Self):
    self.data = take.data^

# Destructor
def __del__(deinit self):
    self.ptr.free()

# @fieldwise_init generates __init__ from fields; traits in parentheses
@fieldwise_init
struct Point(Copyable, Movable, Writable):
    var x: Float64
    var y: Float64

# Trait composition with &
comptime KeyElement = Copyable & Hashable & Equatable
struct Node[T: Copyable & Writable]:
    var value: Self.T          # Self-qualify struct parameters

# Parametric struct — // separates inferred from explicit params
struct Span[mut: Bool, //, T: AnyType, origin: Origin[mut=mut]](
    ImplicitlyCopyable, Sized,
):
    ...

# @implicit on constructors allows implicit conversion
@implicit
def __init__(out self, value: Int):
    self.data = value

# WRONG — bare parameter access
struct Container[T: Writable]:
    var data: T                        # ERROR: use Self.T
    def size(self) -> T:                # ERROR: use Self.T

# CORRECT — Self-qualified
struct Container[T: Writable]:
    var data: Self.T
    def size(self) -> Self.T:
        return self.data

# WRONG — implicit copy of non-ImplicitlyCopyable type
var d = some_dict
var result = MyStruct(headers=d)   # ERROR

# CORRECT — explicit copy or transfer
var result = MyStruct(headers=d.copy())  # or: headers=d^

from std.testing import assert_equal, TestSuite
from std.algorithm import vectorize
from std.python import PythonObject
import std.random

struct MyType(Writable):
    var x: Int

    def write_to(self, mut writer: Some[Writer]):       # for print() / String()
        writer.write("MyType(", self.x, ")")

    def write_repr_to(self, mut writer: Some[Writer]):   # for repr()
        t"MyType(x={self.x})".write_to(writer)           # t-strings for interpolation

struct MyCollection(Iterable):
    comptime IteratorType[
        iterable_mut: Bool, //, iterable_origin: Origin[mut=iterable_mut]
    ]: Iterator = MyIter[origin=iterable_origin]

    def __iter__(ref self) -> Self.IteratorType[origin_of(self)]: ...

# Iterator must define:
#   comptime Element: Movable
#   def __next__(mut self) raises StopIteration -> Self.Element

# Struct field — specify origin explicitly
var _ptr: UnsafePointer[Self.T, MutExternalOrigin]

# Allocate with alloc[]
fn __init__(out self, size: Int):
    self._ptr = alloc[Self.T](size)

struct Span[mut: Bool, //, T: AnyType, origin: Origin[mut=mut]]: ...

from std.testing import assert_equal, assert_true, assert_false, assert_raises, TestSuite

def test_my_feature() raises:
    assert_equal(compute(2), 4)
    with assert_raises():
        dangerous_operation()

def main() raises:
    TestSuite.discover_tests[__functions_in_module()]().run()

for entry in my_dict.items():
    print(entry.key, entry.value)      # direct field access, NOT entry[].key

for key in my_dict:
    print(key, my_dict[key])

# WRONG — no List[T](elem1, elem2, ...) constructor
var nums = List[Int](1, 2, 3)

# CORRECT — bracket literals
var nums = [1, 2, 3]                              # List[Int]
var nums: List[Float32] = [1.0, 2.0, 3.0]         # explicit element type
var scores = {"alice": 95, "bob": 87}              # Dict[String, Int]

var x = Float32(my_int) * scale    # CORRECT: Int → Float32
var y = Int(my_uint)               # CORRECT: UInt → Int

var a: Float32 = 0.5              # literal becomes Float32
var b = Float32(x) * 0.003921    # literal adapts — no wrapping needed
var v = SIMD[DType.float32, 4](1.0, 2.0, 3.0, 4.0)  # literals adapt

# Construction and lane access
var v = SIMD[DType.float32, 4](1.0, 2.0, 3.0, 4.0)
v[0]                              # read lane → Scalar[DType.float32]
v[0] = 5.0                        # write lane

# Type cast
v.cast[DType.uint32]()            # element-wise → SIMD[DType.uint32, 4]

# Clamp (method)
v.clamp(0.0, 1.0)                 # element-wise clamp to [lower, upper]

# min/max are FREE FUNCTIONS, not methods
from std.math import min, max
min(a, b)                          # element-wise min (same-type SIMD args)
max(a, b)                          # element-wise max

# Element-wise ternary via bool SIMD
var mask = (v > 0.0)              # SIMD[DType.bool, 4]
mask.select(true_case, false_case) # picks per-lane

# Reductions
v.reduce_add()                     # horizontal sum → Scalar
v.reduce_max()                     # horizontal max → Scalar
v.reduce_min()                     # horizontal min → Scalar

var s = "Hello"
len(s)                  # 5 (bytes)
s.byte_length()         # 5 (same as len)
s.count_codepoints()    # 5 (codepoint count — differs for non-ASCII)

# Iteration — by codepoint slices (not bytes)
for cp_slice in s.codepoint_slices():
    print(cp_slice)

# Codepoint values
for cp in s.codepoints():
    print(Int(cp))      # Codepoint is a Unicode scalar value type

# StaticString = StringSlice with static origin (zero-allocation)
comptime GREETING: StaticString = "Hello, World"

# t-strings for interpolation (lazy, type-safe)
var msg = t"x={x}, y={y}"

# String.format() for runtime formatting
var s = "Hello, {}!".format("world")

def might_fail() raises -> Int:          # raises Error (default)
    raise Error("something went wrong")

def parse(s: String) raises Int -> Int:  # raises specific type
    raise 42

try:
    var x = parse("bad")
except err:                               # err is Int
    print("error code:", err)

# Function type with capture
comptime MyFunc = fn(Int) capturing[_] -> None

# Parametric function type (for vectorize etc.)
comptime SIMDFunc = fn[width: Int](Int) capturing[_] -> None

# vectorize pattern
from std.algorithm import vectorize
vectorize[simd_width](size, my_closure)

AnyType
  ImplicitlyDestructible          — auto __del__; most types
  Movable                         — __init__(out self, *, deinit take: Self)
    Copyable                      — __init__(out self, *, copy: Self)
      ImplicitlyCopyable(Copyable, ImplicitlyDestructible)
    RegisterPassable(Movable)
      TrivialRegisterPassable(ImplicitlyCopyable, ImplicitlyDestructible, Movable, RegisterPassable)