has · Builtins · MPL Reference

`has (schema itemName -- hasName)`

Inputs

schema: Object or Ref object whose dereferenced schema is searched for the requested name.
itemName: Known non-NIL Text name being tested for presence.

Outputs

hasName: Known Cond result that is TRUE when at least one matching name exists.

Tests whether the dereferenced schema contains at least one item matching the requested known name.

has uses the same name-matching rules as fieldIndex, but it stops at presence and does not return which ordinal matched.

Behavior

For Dict, the result is TRUE if at least one field has the requested name.
For Dict, duplicate matching names still produce only TRUE; the builtin never reports which ordinal matched.
For Dict, the empty name "" also matches unnamed items.
For List and Tuple, only the empty name "" matches, and it matches only when the Struct object is non-empty.
For all other schemas, the result is FALSE.

Example

{} () {} [
  mixed: { 1 "" def x: 1; y: 2; };

  "-- Dict field names --" printCompilerMessage
  mixed "x" has printStack _:;
  @mixed "x" has printStack _:;

  "-- empty name --" printCompilerMessage
  mixed "" has printStack _:;
  (1 FALSE) "" has printStack _:;
  () "" has printStack _:;

  "-- missing name --" printCompilerMessage
  mixed "z" has printStack _:;
  (1 FALSE) "x" has printStack _:;
] "main" exportFunction

Expected Output During Compilation

-- Dict field names --
TRUE
TRUE
-- empty name --
TRUE
TRUE
FALSE
-- missing name --
FALSE
FALSE