Syntax of statements and expressions

Abort

abort
  skip
with (
  skip;
  skip
)

Execute the first statement, but permanently terminate this execution when the other statements execute.

Delay

delay 1

Postpone the execution with a number of time units (integer or real).

Guard

[true] skip

Block the statement whenever the guard does not evaluate to true. The evaluation of the condition and the execution of the statement together form a single execution step.

If

if true then
  skip
else
  skip
fi

Depending on whether the condition evaluates to true, execute the first or the second body statement. The evaluation of the condition and the execution of any of the body statements are two separate execution steps.

Interrupt

interrupt
  skip
with (
  skip;
  skip
)

Execute the first statement, but temporarily suspend this execution when the other statements execute (possibly multiple times).

Parallel

par
  skip
and
  skip
rap

Execute multiple statements in parallel, in an interleaved way. Communication and synchronization within a process can only be performed through shared variables.

Process method call

method()()

Invoke a process method with a series of input parameter values and a series of output variables. If the process method call is the last statement of a method, then there is no danger of stack overflow.

Select

sel
  skip
or
  skip
les

Non-deterministic choice between multiple alternative statements. It is blocked when all alternatives are blocked. The choice is finally resolved by the first statement that executes. Fairness of the choice is not guaranteed.

Skip

skip

Execute without any observeable effect on variables or messages. If used in the context of a sel statement, a skip statement is never blocked, and can resolve the choice. This can be used to model an internal decision.

Receive

port?msg(var1, var2 | true)

Receive a message over a port, and assign the message parameters to variables. The (optional) condition restricts the accepted parameter values.

Send

port!msg(expr1, expr2)

Send a message over a port, and add the expressions as message parameters.

Switch

switch nil do
  case 42 then
    skip
  default
    skip
od

Evaluate the switch expression and all case expressions. Afterwards execute the body statement of a case with an expression that equals the switch expression. If no such case exists, then execute the default body statement.

The evaluation of all expressions and the execution of any of the body statements are separate execution steps.

While

while true do
  skip
od

As long as the condition evaluates to true, execute the statement. The evaluation of the condition and the execution of the statement are two separate execution steps.

Assignment

v := nil

Current time

currentTime

Data method call

"foo" printString()

If

if true then
  nil
else
  nil
fi

Depending on whether the condition evaluates to true, return the first or the second body expression.

New

new(Object)

Create a new instance of a data class.

Return

return nil

Self

self

Super

self^

Switch

switch nil do
  case 42 then
    nil
  default
    nil
od

Evaluate the switch expression and all case expressions. Afterwards return the body of a case with an expression that equals the switch expression. If no such case exists, then execute the default body.

While

while true do
  nil
od

As long as the condition evaluates to true, evaluate the body expression. Finally return nil.