new-typedb-fun

name	new-typedb-fun
description	Use when defining a new TypeDB 3 `fun` function in a schema file. Provides correct boilerplate and inlines the constraints that cause the most common parse and type errors.

New TypeDB 3 fun Function

Boilerplate Templates

Set-returning function

fun function_name($arg: ArgType) -> { ReturnType }:
  match
    {
      # branch A — unique variable names: $a_x, $a_y, ...
    } or {
      # branch B — unique variable names: $b_x, $b_y, ...
    };
  return { $result };

Single-value function

fun function_name($arg: ArgType) -> ReturnType:
  match
    $result isa ReturnType;
    # ...
  return first $result;

Aggregate (count / max / min)

fun function_name($arg: ArgType) -> integer:
  match
    # ...
  return count;

fun function_name($arg: ArgType) -> double:
  match
    $val isa ...; # ...
  return max($val);

Critical Constraints

Variable naming

• Each OR branch must use unique variable names.
• Never name a variable after a type or role.

Relation syntax inside fun

# CORRECT
$r isa some_relation;
$r links (role: $x);

# WRONG
$r (role: $x) isa some_relation;

Function-call results across OR branches

# WRONG
{ let $out = some_fun($a); } or { let $out = some_fun($b); }

# CORRECT
{ let $tmp = some_fun($a); let $out = $tmp; } or { let $tmp2 = some_fun($b); let $out = $tmp2; }

Recursion

• Mutual recursion between two fun functions is not supported.
• Self-recursion is allowed.

Hoisting constraints

• links constraints can be hoisted before the outer { } or { } block.
• isa constraints before the outer OR block cause parse errors and should stay inside branches.

No rule blocks

• TypeDB 3 does not support rule in define. Use fun only.

plays role-player type checking

• Every isa SomeType in an OR branch must be a valid player of the matched role.

OR Branch Ordering

For batch / all-rules queries, put the branch matching the most inputs first.

For return first functions, early-exit applies. For return min / return max, all branches are evaluated, so ordering has no early-exit benefit.

Calling a fun in a query

# Set-returning: iterate results
let $result in function_name($arg);

# Single-value: bind and use
let $val = function_name($arg);
$val > 0;

# Boolean guard pattern
true == bool_function($arg);