What does this expression mean?

[linwaytin]

Hi community,

I'm new to Nim and try to learn the basics from Exercism.  
In the exercise `React`, I need to implement a spreadsheet-like function.  


This exercise has little information and thus I have to figure out the 
structure of the code from the test suite as follows. 
    
    
    suite "React":
      test "setting the value of an input cell changes the observable value":
        let
          reactor = newReactor()
          i1 = reactor.createInput(1)
        check i1.value == 1
        i1.value = 2
        check i1.value == 2
      
      test "the value of a compute is determined by the value of the 
dependencies":
        let
          reactor = newReactor()
          i1 = reactor.createInput(1)
          # Using @[Cell i1] to avoid the compiler inferring the array type as 
seq[InputCell],
          # which is incompatible with seq[Cell].
          c1 = reactor.createCompute(@[Cell i1], proc(vals: seq[int]): int = 
vals[0] + 1)
        check c1.value == 2
        i1.value = 2
        check c1.value == 3
    
    
    Run

I have no idea of what `@[Cell i1]`, mentioned in the comment, means.  
Does anybody have some idea?  


Thank you.