Rethink arrow operators

Currently we have arrow operators such as in
```
x ~~(p:Int)~~>y1
 +~~(s:String)~~y2
```
With the Smalltalk style method calls we split up the method name, but keep the commas (unlike in Scala). We could do something similar for the arrows, to get rid of the ugly plus characters:
```
x ~~(p:Int)~~>y1,
  ~~(s:String)~~>y2
```
or
```
x ~~(p:Int)~~>y1
 ,~~(s:String)~~>y2
```
