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Function Statements

Function Statements

Function statements define reusable custom functions that can be called throughout your Trilogy scripts.

Syntax

syntax-example
function: "def" IDENTIFIER "(" function_binding_list ")" "->" expr
function_binding_item: IDENTIFIER function_binding_type? function_binding_default?
function_binding_type: ":" (data_type | validated_type)
function_binding_default: "=" expr

Basic Function

Define a simple function:


def double(x) -> x * 2;

With Type Hints

Specify parameter types:


def calculate_tax(amount: float, rate: float) -> amount * rate;

With Default Values

Provide default parameter values:


def apply_discount(price, discount = 0.1) -> price * (1 - discount);

Calling Functions

Use @ prefix to call custom functions:


def format_currency(amount) -> concat('$', cast(round(amount, 2) as string));
select
    order.id,
    @format_currency(order.total) -> formatted_total
;

Complex Functions

Functions can use expressions, including conditional logic:


def categorize_amount(amount) ->
    case
        when amount > 1000 then 'high'
        when amount > 100 then 'medium'
        else 'low'
    end;

Constrained Parameters

Constrained parameter types reject out-of-domain literal arguments:

def discounted(price: float, rate: float[0..1] = 0.1) -> price * (1 - rate);
select @discounted(100.0, 0.2) as discounted_price;

Passing 2.0 as the rate is an authoring error. A concept argument is not scanned when a function is called; its data constraints belong on the concept declaration and are checked through datasource validation.

Reusable Assertions

Functions can return a boolean aggregate check for datasource assert clauses:

def retains_rows(row_id, fraction = 0.75) ->
    count(row_id) >= fraction * prior(count(row_id));
key record_id int;
datasource records (record_id)
grain (record_id)
address records
assert @retains_rows(record_id)
;

prior(...) is only meaningful within a datasource assertion. Functions from an aliased module are called as @alias.function_name(...); see Functions & Imports.

Use Cases

  • Reusable business logic
  • Standardized calculations
  • Code organization
  • DRY principle

Example


# Define helper functions
def margin(revenue, cost) -> (revenue - cost) / revenue;
def growth_rate(current, previous) -> (current - previous) / previous * 100;
import order as order;
select
    order.product_id,
    sum(order.revenue) -> total_revenue,
    sum(order.cost) -> total_cost,
    @margin(total_revenue, total_cost) -> profit_margin
;