ExpectPreconditionWithReason
Type
statement
Summary
Check a precondition, with a reason
Syntax
expect [that] <Condition> because <Reason>
Description
Use this statement at the start of a handler to check that necessary preconditions for the handler are satisfied. For example, the handler may require that its parameters have a particular structure or fall within a particular range, or may need the system to be in a specific state.
If the Condition is false, an error will be thrown including the Reason for the check.
Parameters
| Name | Type | Description |
|---|---|---|
Condition | Expression that must be true for code to work | |
Reason | Description of the precondition |
Examples
-- Draw a random variate from the Bernoulli distribution with
-- parameter pParam. A Bernoulli variate may be 0 or 1; the
-- parameter pParam is the probability that the result is 1.
handler BernoulliVariate(in pParam as Number) returns Number
expect (pParam >= 0 and pParam <= 1) \
because "Bernoulli parameter must be a probability in [0,1]"
if (any number <= pParam) then
return 1
else
return 0
end if
end handler
Related
statement: ExpectPrecondition