Introspection & Debug

CXL provides 4 introspection methods and 1 debug method. These are the only methods that accept null receivers without propagating null – they are designed specifically for inspecting and handling null values.

type_of() -> String

Returns the type name of the receiver as a string. Works on any value, including null.

Type name strings: "String", "Int", "Float", "Bool", "Date", "DateTime", "Null", "Array", "Map".

$ cxl eval -e 'emit a = 42.type_of()' -e 'emit b = "hello".type_of()' \
    -e 'emit c = null.type_of()'

{
  "a": "Int",
  "b": "String",
  "c": "Null"
}

Useful for branching on dynamic types:

emit formatted = match value.type_of() {
  "Int"   => value.to_string() + " (integer)",
  "Float" => value.round_to(2).to_string() + " (decimal)",
  _       => value.to_string()
}

is_null() -> Bool

Returns true if the receiver is null, false otherwise. This is the primary way to test for null values – it is NOT subject to null propagation.

$ cxl eval -e 'emit a = null.is_null()' -e 'emit b = 42.is_null()'

{
  "a": true,
  "b": false
}

Use in filter statements:

filter not field.is_null()

is_empty() -> Bool

Returns true for empty strings, empty arrays, or null values. Returns false for all other values.

$ cxl eval -e 'emit a = "".is_empty()' -e 'emit b = "hello".is_empty()' \
    -e 'emit c = null.is_empty()'

{
  "a": true,
  "b": false,
  "c": true
}

Useful for filtering out blank or missing records:

filter not name.is_empty()

catch(fallback: Any) -> Any

Returns the receiver if it is non-null, otherwise returns the fallback value. This is the method equivalent of the ?? operator.

$ cxl eval -e 'emit a = null.catch("default")' \
    -e 'emit b = "present".catch("default")'

{
  "a": "default",
  "b": "present"
}

catch and ?? are interchangeable:

# These two are equivalent:
emit name = raw_name.catch("Unknown")
emit name = raw_name ?? "Unknown"

debug(label: String) -> Any

Passes the receiver through unchanged while emitting a trace log with the given label. Zero overhead when tracing is disabled. The return value is always the receiver, making it safe to insert into any expression chain.

$ cxl eval -e 'emit result = 42.debug("check value")'

{
  "result": 42
}

Insert debug anywhere in a method chain for inspection without affecting the output:

emit total = price.debug("price")
    * qty.debug("qty")

When tracing is enabled, this produces log lines like:

TRACE source_row=1 source_file=input.csv: price: Integer(100)
TRACE source_row=1 source_file=input.csv: qty: Integer(5)

Null-safe summary