? modifier

[Mouvedia]

//if this object wasn't previously set this would set it
@object ? name { … }

@value example { keywordA }
@value example2 { … }
   & ? example { keywordB }

//this would use keywordA since example was already set
property: example;

It's quite useful when you rely on third party hss.

alternate proposal

Since we can't start an object name wth a ? we could either get rid of the space or make it optional.

@object ?name { … }

concequense

//since
#new name { … }
//is equivalent to
#new @container name { … }
//then
#new ? name { … }
//is equivalent to
#new @container ? name { … }

Which means that the ? will be scope aware when used with the new instruction and that this construct will replace the ensure instruction.

//example with several elements
#new @container elementA & ? elementB { … }
//is equivalent to
#new elementA & ? elementB { … }

PS: depends on axr/core#190

Question

//should we allow
?@object nameA & nameB { … }
//to resolve to
@object ? nameA & ? nameB { … }
//which would mean we would also have to accept
!#support (A) & (B) { }
//which would be equivalent to
#support !(A) & !(B) { }

[Mouvedia]

Coffeescript has the existential operator and Roole has the conditional assignment operator ?=.

It's also pretty useful to set a default fallback placed after in the source. So for example if an user chose not to do something we would have a default dynamically set afterwards.