language-deep-dive7 min

Iteration Patterns

Clean Language has several ways to iterate, each suited to a different problem. Ranges for counted loops, list iteration for collections, while for unknown counts. break and continue give you fine control when you need it.

Three iteration forms — range, step, and list:

start:\n    string evens = ""\n    iterate n in 2 to 10 step 2\n        evens = evens + n.toString() + " "\n    print("Evens: " + evens)\n\n    list<string> days = []\n    days.add("Mon")\n    days.add("Tue")\n    days.add("Wed")\n    iterate day in days\n        print("Day: " + day)\n\n    integer n = 1\n    integer total = 0\n    while n <= 5\n        total = total + n\n        n = n + 1\n    print("Sum 1-5: " + total.toString())

Evens: 2 4 6 8 10 \nDay: Mon\nDay: Tue\nDay: Wed\nSum 1-5: 15

iterate n in 2 to 10 step 2 counts by twos. iterate day in days loops over every element by value — no index needed. while n <= 5 runs until the condition is false — use this when the count depends on logic.

break exits early; continue skips to the next iteration:

start:\n    list<string> names = []\n    names.add("Alice")\n    names.add("Bob")\n    names.add("Charlie")\n    names.add("Diana")\n\n    string search = "Charlie"\n    integer found_at = -1\n    iterate i in 0 to names.length() - 1\n        if names[i] == search\n            found_at = i\n            break\n\n    print(search + " at index: " + found_at.toString())\n\n    string result = ""\n    iterate name in names\n        if name.length() < 5\n            continue\n        result = result + name + " "\n    print("Long names: " + result)

Charlie at index: 2\nLong names: Alice Charlie Diana

break exits the iterate block immediately — the search stops as soon as Charlie is found. continue skips to the next iteration — names shorter than 5 characters are skipped. Both work in iterate-range, iterate-list, and while loops.

Quick recap

iterate n in start to end — range loop, inclusive on both ends
iterate n in start to end step N — count by N each iteration
iterate item in myList — loop over every element by value
break exits the loop; continue skips to the next iteration