Immutable Values with define and bind

Goal: name values without introducing mutation or moving pure logic into a handler.

Syntax

Module constant:

source.tb

define Name as Type = literal

Local value inside a block:

source.tb

bind name as Type = expression

define is visible in the module. bind is visible only in the flow where it is declared.

Example

review-score.tb

module examples.review_score

define ScoreLimit as Float = 0.75
define AcceptedLabel as Text = "accepted"
define ReviewLabel as Text = "review"

function ReviewScore
    takes score as Float
    takes bonus as Float
    gives Text
    do
        bind adjusted as Float = (score + bonus) / 2.0
        bind accepted as Boolean = adjusted >= ScoreLimit
        if accepted
            give AcceptedLabel
        else
            give ReviewLabel

Compile

Terminal

touba compile review-score.tb --out review-score.air.json

The AIR contains:

• constants in definitions.constants;
• pure calculations in AIR expressions;
• local bind values as graph nodes.

Run

Terminal

touba run review-score.air.json --inputs-json '{"score":1.0,"bonus":0.8}' --output result

Expected output:

Output

"accepted"

The output is a JSON string, including the quotation marks. Invalid, missing or extra entry fields are refused before execution. You can check the typed entry refusal without changing the program:

Terminal

if touba run review-score.air.json --inputs-json '{"score":"invalid","bonus":0.8}' --output json; then
  exit 1
else
  test "$?" -eq 1
fi

Useful Errors

This constant is refused:

source.tb

define BaseScore as Float = 0.5
define ScoreLimit as Float = BaseScore + 0.25

Reason: define accepts only literals. The calculation must live in a function or in a local bind.

This local value is refused:

source.tb

bind accepted as Boolean = title

Reason: the declared type is Boolean, while the expression produces Text.

Takeaway

Use define for non-sensitive thresholds or labels. Use bind to make a local calculation readable and traceable.

Do not use define for an API key, token, environment variable, or value that changes across execution environments.