Types
The languages supports the types Strings, Booleans, Integers, and Floats. Null
is a valid value of every type.
Syntax
expr ::= expr && expr # Conjunction ("and")
| expr || expr # Disjunction ("or")
| expr < expr
| expr > expr
| expr = expr
| expr != expr
| expr ++ expr # String concatenation
| expr + expr # Also works for string concatenation
| expr ** expr # generic exponential function
| ( expr )
| const
| var
const ::= ('"'[^'"']*'"') | ('\''[^'\'']*'\'') # string
| ('-'? digit+) # int
| ('-'? digit+ '.' digit+) # double
| true
| false
| null
var ::= (char|['_' '$'])(char|['-' '_' '\'']|digit)* # identifier
Examples of constant expressions:
1
10.0
"A string"
null
true
false
Reserved keywords
The following list of reserved keywords cannot be used for activity ids.
Semantics
Variables var refer to events in scope at the location of the expression;
see [articles/location.md] for details.
Less-than and greater-than operators convert between numeric types, and return
false if either side is null.
Examples
An expression that evaluates to true if the event Amount is greater than 10000:
Amount > 10000
An expression that evaluates to true if the event Type is equal to the
string Architect or null.
Type == "Architect" || Type == null
An expression that evaluates to true if the event Amount plus 1000 is greater
than 10000 or less than 20000:
(Amount + 1000 > 10000) || (Amount + 1000 < 20000)
Programmatic specification
Expressions are constructed programmatically using the
Expression class.
Use the from-string constructor
which parses an expression from a string:
Expression e = new Expression("I > 1000");
Use expressions to construct guarded relations. E.g., to construct
a condition from top-level event “G” to top-level event “H” which
is active only when the top-level event “I” has a value greater than 1000:
graph.AddCondition("G", "H", null, new Expression("I > 0"), null);
You can check whether an expression is syntax and type-correct in a
particular graph using the call
CheckExpression.
