Loops

Loops let you repeat actions. Bop has three kinds: repeat, while, and for...in.

repeat

The simplest loop — just “do this N times.” No loop variable, no fuss:

repeat 4 {
  print("Hello!")
}

The count can be any expression:

let times = 3
repeat times {
  print("Again!")
}

repeat is perfect when you just need repetition without tracking a counter.

while

Loops as long as a condition is true:

let n = 1
while n <= 100 {
  n *= 2
}
print(n)    // 128

A while true loop runs forever (until you break out of it or hit the step limit):

let total = 0
let i = 1
while true {
  total += i
  if total > 100 {
    break
  }
  i += 1
}
print("Sum exceeded 100 at i=" + i.to_str())

Counting example

// Count how many numbers under 50 are divisible by 7
let count = 0
let n = 1
while n < 50 {
  if n % 7 == 0 {
    count += 1
  }
  n += 1
}
print("Found " + count.to_str())

for…in

Iterates over ranges, arrays, or dictionary keys.

Ranges

for i in range(5) {
  print(i.to_str())     // 0, 1, 2, 3, 4
}

With a start value:

for i in range(2, 8) {
  print(i.to_str())     // 2, 3, 4, 5, 6, 7
}

Arrays

let fruits = ["apple", "banana", "cherry"]
for fruit in fruits {
  print(fruit)
}

Dictionary keys

let scores = {"Alice": 95, "Bob": 87, "Charlie": 92}
for name in scores {
  let s = scores[name].to_str()
  print(name + ": " + s)
}

Iterators and user-defined containers

for x in v works on anything that participates in the iterator protocol: arrays, strings, dicts, explicit iterators (arr.iter()), and user types that implement .iter():

struct Bag { items }
fn bag_of(arr) { return Bag { items: arr } }
fn Bag.iter(self) { return self.items.iter() }

let b = bag_of([10, 20, 30])
for v in b { print(v) }         // 10  20  30

That’s the structural-typing story: no trait declaration, no ceremony — if v.iter() returns something iterable, for x in v just works.

Strings

You can iterate over the characters of a string:

let word = "hello"
for ch in word {
  print(ch)    // "h", "e", "l", "l", "o"
}

Nesting loops

Loops can be nested. This is useful for working with grids or combinations:

for row in range(3) {
  for col in range(4) {
    print("(" + row.to_str() + ", " + col.to_str() + ")")
  }
}