Loops Reference

Compact reference for loop forms.

Syntax

while condition { ... }
for i: int in 0..10 { ... }
for i: int in 0...10 by 2 { ... }
foreach item: str in items { ... }

while

Runs while the condition stays truthy.

for

• Loop variable must be typed as int
• .. is inclusive; ... is exclusive
• Optional by sets the step
• Start, end, and step convert to int at runtime
• by 0 aborts (E2702)
• Dedicated numeric for does not allocate a list

Range as a value (0.7.4)

start...end and start..end (optional by step) are expressions that produce a list of int, matching rangeList / rangeListInclusive for step 1.

xs: list = 0...5;          // [0, 1, 2, 3, 4]
ys: list = 0..5;           // [0, 1, 2, 3, 4, 5]
zs: list = 0...10 by 2;

for i: int in 0...10 stays the non-allocating loop. foreach i: int in 0...10 iterates the allocated list value. Slice syntax stays colon (xs[1:4]); xs[0...10] indexes with a list and is a type error.

foreach

• Iterates a runtime iterable (list, or hash keys as str)
• Each element is checked against the declared binding type

break and continue

Only valid inside loops.

Common Mistakes

• for i: str in 0..10 { ... } — loop var must be int
• break; outside a loop
• by 0 — aborts (E2702)

See Also

• Control Flow
• Errors and Troubleshooting