Help understanding verse syntax on race w/ verse persistance template

[t.tutiya]

Hi.
The inequality in the “decides” function acts like an exception checker.

FuncA(arg1:int)<decides><transacts>:void = 
    arg1 > 0

If “arg1 > 0” is true, nothing happens.
If “arg1 > 0” is false, the function fails (like an exception call).