Loops

Draft provides several looping constructs for iteration.

For Loop

Iterate over a range or collection:

@// Range iteration
for @i in 0..10
    write(@i)
fin for.

@// Exclusive range
for @i in 0..<10
    write(@i)
fin for.

Iterating Arrays

@fruits = ["apple", "banana", "cherry"]
for @fruit in @fruits
    write(@fruit)
fin for.

Iterating with Index

for @index, @fruit in @fruits
    write(string(@index) + ": " + @fruit)
fin for.

Iterating Maps

@scores = {"Alice": 95, "Bob": 87, "Charlie": 92}
for @name, @score in @scores
    write(@name + ": " + string(@score))
fin for.

Iterating Strings

for @char in "Hello"
    write(@char)
fin for.

While Loop

Execute while a condition is true:

mut @count = 0
while @count < 10
    write(@count)
    @count = @count + 1
fin while.

Infinite Loop

while true
    @input = read_line()
    if @input == "quit"
        break
    fin if.
    process(@input)
fin while.

Loop Control

Break

Exit the loop immediately:

for @i in 0..100
    if @i == 50
        break
    fin if.
    write(@i)
fin for.

Continue

Skip to the next iteration:

for @i in 0..10
    if @i % 2 == 0
        continue
    fin if.
    write(@i)  @// Only odd numbers
fin for.

Break with Value

Return a value from a loop:

@result = for @i in 0..100
    if @i > 50
        break @i
    fin if.
fin for.
@// result = 51

Nested Loops

for @i in 0..3
    for @j in 0..3
        write(string(@i) + "," + string(@j))
    fin for.
fin for.

Labeled Loops

Break or continue outer loops:

outer: for @i in 0..10
    inner: for @j in 0..10
        if @i * @j > 50
            break outer
        fin if.
    fin for.
fin for.

Loop Expressions

Loops can return values:

@sum = for @i in 1..10
    @i * @i
fin for.
@// sum = 1 + 4 + 9 + 16 + 25 + 36 + 49 + 64 + 81 + 100 = 385

Iterators

Create custom iterators:

record Counter
    current: Int
    max: Int
fin record.

impl Iterator for Counter
    action next(@self: Counter) -> Option<Int>
        if @self#current < @self#max
            @value = @self#current
            @self#current = @self#current + 1
            return some(@value)
        fin if.
        return none
    fin action.
fin impl.

@counter = Counter { current: 0, max: 10 }
for @value in @counter
    write(@value)
fin for.

Common Patterns

Collect Results

@squares = for @i in 1..10
    @i * @i
fin for.
@// squares = [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

Find First Match

@first_even = for @i in 1..100
    if @i % 2 == 0
        break @i
    fin if.
fin for.
@// first_even = 2

Filter and Transform

@evens_squared = for @i in 1..20
    if @i % 2 == 0
        @i * @i
    fin if.
fin for.

Next Steps

Learn about Objects and Enums for data structures.