Statements

Statements are used in process syntax to

• destruct values: Command
• bind values: LetStatement

Process syntax is a series of statements, where all are nonterminating. In a channel expression the last one will be terminating, making it an exception.

Process syntax is introduced by the Proces Rule:

^Syntax
Process : (Statement (;^? Statement) (;^? TerminatingStatement)^?)^?

Statement :
      Command
   | LetStatement

TerminatingStatement :
      TerminatingCommand

It is used in the following places:

• do expressions:

  let x = do { process } in value
  

  The process here may not use terminating statements.

• channel expressions:

  let x = chan dual { process }
  

  The process here must use a terminating statement. It constructs x by destructing its dual, dual.

Let Statements

^Syntax
LetStatement :
      let Pattern = Expression

Let statements are used to create values in processes. They are the only constructive statements, as commands always destruct.

In do expressions, they are used to bind the values used in the value after in:

let true_and_false = do {
  let x: Bool = .true!
  let y: Bool = .false!
} in (x, y)!

In chan expressions, they can be used to construct a value that is then linked with a value of dual type:

def just_true = chan return: chan Bool {
  // constructing the return value
  let b: Bool = .true!
  // linking it
  return <> b
}
// is equivalent to
def just_true = chan return: chan Bool {
  // destructing the result
  return.true!
}