With stage

The with stage in a data pipeline allows the local declaration of functions, which can then be used as part of the pipeline.

Syntax

with <function-declaration>
... # continue pipeline, may call functions in patterns

where <function-declaration> is a function declaration.

Behavior

The with stages in a data pipeline must precede any other kind of stage (together, all with stages are referred to as the pipeline preamble)
with stages must be followed by other data pipeline stages, i.e. with stages by themselves do not consitute a valid data pipeline.
Function declarations in the preamble of a data pipeline are only valid within that pipeline (declared functions may be called in match and fetch stages).

Validation

The usual function validation applies to the function declaration in a with clause.

Examples

Find users with more friends than a specific user and return their usernames

with fun friend_count($user: user) -> integer:
  match friendship($user, $x)
  return count;
match
  $user1 isa user, has username "<name>";
  $user2 isa user, has username $name;
  friend_count($user1) < friend_count($user2);
select $name;

Return all “popular” users in the database

with fun friend_count($user: user) -> integer:
  match friendship($user, $x)
  return count;
with fun popular_users() -> { user }:
  match
    $x isa user;
    friend_count($x) > 500;
  return { $x };
match
  let $y in popular_users();
  $y has username $pop_name;
select $pop_name;