help writing a conditional access operator

[mat]

I have just started playing with nim and like it enormously so far.

I have written a nimble module 'elvis' to expose some syntactic sugar for 
working with truthy, ternary and conditional assignment operators which is 
avialable 
[https://github.com/mattaylor/elvis](https://github.com/mattaylor/elvis) . All 
is looking good and working well but any advice from more experienced nim folks 
(nims?, nimers?, nimblers?) would be much appreciated.

I would also like to add a conditional access operator 'a .? b' which only 
invokes the right operand if the left operand is 'truthy' and otherwise returns 
am uninitiated instance of whatever a.b would have returned.

I have trying with templates like..
    
    
    template `?.`*[T,U,V](left: T, right: proc (x: T, y: U): V): V =
      if ?left: right(left) else: (var r:V)
    
    template `?.`*[T,U](left: T, right: U): U =
      if ?left: left.right else: (var r:U)
    
    
    Run

But the compiles seems to be getting confused when I call it eg..
    
    
    nim> import elvis
    nim> assert ?""
      false`  [AssertionError]
    nim> ""?.len
    template/generic instantiation from here
    ../../Volumes/Mat/work/nimby/elvis/elvis.nim(50, 35) Error: invalid type: 
'HSlice[len.U, len.V]' in this context: 'proc (x: HSlice[len.U, len.V]): 
int{.inline, noSideEffect.}' for var
    
    
    Run

Not sure what I am doing wrong here.