Conditions and iteration

This guide explains how to express a deterministic business rule in Touba. A computable decision does not need a model.

Choose a path

if / else if / else evaluates conditions in order and runs the first selected branch. Each condition must be a Boolean. These controls compose inside functions, skills and strategies.

triage.tb

module examples.triage

type Ticket
    id is Text
    overdue_days is Int
    active is Boolean

function FirstAction
    takes tickets as List of Ticket
    gives Optional of Text
    do
        for ticket in tickets
            if ticket.active
                if ticket.overdue_days >= 7
                    give some("Urgent: " ++ ticket.id)
                else if ticket.overdue_days >= 3
                    give some("Follow up: " ++ ticket.id)
        give none(Text)

The function walks tickets in input order and returns an action for the first active ticket needing attention: urgent from seven days, follow-up from three days. If none matches, it returns absence. It does not sort tickets by urgency.

Iterate without implicit mutation

• for item in items walks a typed list in order.
• bind and into results are local to their block; they do not reassign a variable in the caller's scope.
• give ends the current call, including from a nested loop.
• while uses the host limit max_loop_iterations (100 by default). Reaching this limit produces a runtime refusal. There is no source max_iterations clause. See the syntax reference.

A loop does not introduce a mutable accumulator. To transform each item into a result, use a typed target inside a strategy or skill and bounded parallelism. For a first-match search, a for loop with an early return is appropriate.

Preserve execution controls

bounded-loop.tb

module examples.bounded_loop
function Wait
    takes repeat as Boolean
    gives Text
    do
        while repeat
            bind observed as Boolean = repeat
        give "Ready"

touba compile bounded-loop.tb --out bounded-loop.air.json
touba run bounded-loop.air.json --entry function:examples.bounded_loop/Wait --inputs-json '{"repeat":false}' --max-loop-iterations 3 --output json

With false, the result is Ready. With true, the host stops the loop after three iterations. CLI option --max-loop-iterations sets the runtime's max_loop_iterations limit.

Repeating a call grants no additional authority. Declared capabilities, grants, scopes and run budgets remain checked on every call. An authorized capability may be used repeatedly while its constraints permit it.

Loops and conditions do not prevent human pauses: the continuation preserves the calls and scopes needed for resumption. See Durable recovery to choose the right mechanism.

Try it

The classification tutorial combines enums, optionals and branches with JSON inputs and verifiable results.

For a closed enum choice, use match / case. The compiler checks that every member is handled exactly once.