Bugzilla – Full Text Bug Listing
| Summary: | Support return values for loop-expressions | ||
|---|---|---|---|
| Product: | [Modeling] TMF | Reporter: | Moritz Eysholdt <moritz.eysholdt> |
| Component: | Xtext | Assignee: | Project Inbox <tmf.xtext-inbox> |
| Status: | CLOSED WORKSFORME | QA Contact: | |
| Severity: | enhancement | ||
| Priority: | P3 | CC: | knut.wannheden |
| Version: | unspecified | ||
| Target Milestone: | --- | ||
| Hardware: | PC | ||
| OS: | Mac OS X - Carbon (unsup.) | ||
| Whiteboard: | |||
Maybe I've missed the point, but isn't it always possible to achieve the same result using higher order functions like filter(), map(), reduce(), and fold()? E.g. val result = if (integerList.exists(e|e == 5)) "foo" val result = if (integerList.exists(e|e == 5)) "foo" else "bar" val result = integerList.filter(e|e<5).map(e|e) I have probably missed the point, but IMHO using higher order functions is even more declarative. In fact I wouldn't use for loops as much in Java if higher order functions were as concise as in Xtend2. |
Xtend2 supports while-loops and foreach-loops. Both loops are expressions, but they doen't have return values. To allow an even more declarative programming style, it would be nice to allow return values. I think it's a good idea to distinguish between single-value return values and multi-value return values. Actually, these are loop-canceling expressions and expressions that don't cancel loop execution. Example 1: Use "break" for loops like "return" for methods: ---- val result = for(i:integerList) { if(i == 5) { break "foo" } } ---- expect result to be "foo" if the list contains the number 5, void otherwise. ---- val result = for(i:integerList) { if(i == 5) { break "foo" } } default "bar" ---- expect result to be "foo" if the list contains the number 5, "bar" otherwise. Example 2: initalize a list within a loop: --- val result = newArrayList() : for(i:integerList) { if(i < 5) { add(i) } --- expect result to contain all values from integerList that are smaller than 5. another syntax for the same expression might be: --- val result = for(i:integerList -> newArrayList()) { if(i < 5) { add(i) } --- potential problem: the returned list is an implicit receiver and I'm not sure if we do or want to suport this (I like it). The same kinds of concepts can be applied to while-loops.