Fallbacks
A fallback, (or fallback expression) is an optional component of a getter that can return a default value if the getter fails (such as due to a missing variable, index, or key).
A fallback expression only runs if the data requested by the associated getter is not found; otherwise, it is ignored completely.
To use a fallback, it must be added to the end of the accessor, within the brackets, with a leading ?
character as shown below.
Example
# Store a value to use as a fallback
<$fallback = "I don't exist!">
{
# Define a variable `foo`
<$foo = "I exist!">
# Get `foo` with fallback
<foo ? <fallback>> # -> "I exist!"
}\n
# Getting `foo` again out of scope will trigger the fallback
<foo ? <fallback>> # -> "I don't exist!"
# Getting `foo` without a fallback here would crash the program
<foo> # error