Expressions

Expressions are function chains applied to particular values, most often during transitions. Expressions can include Transformers and Predicates, and are generally nested function calls around some property key, so Expression is either a <PROPERTY_NAME>, a <FUNC_OPERATOR>(<PROPERTY_NAME>[,<CONSTANT_ARGS>...]) or a <FUNC_OPERATOR>(<FUNC_OPERATOR>), i.e.

• index : returns value of index key in a related source object
• sum(index,2) : returns arithmetic result index+2, where index is converted to decimal
• round(sum(index,2)) : return the rounded result of a previous operation

Bound Property

In any case, an Expression has a primary operand which is hereby called Bound Property. The Property is always the first (leftmost) argument in the tree of calls. Bound Property is the one that will receive a default value, if set. Other properties used in an Expression can't have a default value. This limitation is intentional and aims to force explicitness and reduce the probability of an undesired pitfall in code.

Recursion

Using recursion is allowed, however, maximum depth of stack in any Expression is 8. This limitation is intentional, forcing you to explicitly define complex composition of functions as a new function.

Multiple properties

An Expression can reference more than one property as arguments of functions, but all except for the leftmost one are not considered Bound Properties

Null Property

If the most deeply nested function of an Expression does not require a parameter, the Bound Property is considered to equal Null for the sake of unification. This value would be passed as an argument to the function if its definition does actually have a parameter. Example:

• random(): returns Math.random() value, compare to random, which would be a property reference
• if(isGreater(random(),0.5),f1(some_property),f2(some_property)): applies one of two functions f1,f2 to some_property randomly with 50% chance. However, since the leftmost argument is absend, the Bound Property is Null