github.com/goplus/gop@v1.2.6/printer/_testdata/12-Select-comprehension/select.gop (about)

     1  a := [2, 3, 5, 7, 9, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59]
     2  where := {i for i, v <- a if v == 19}
     3  println("19 is at index", where)
     4  
     5  if at, ok := {i for i, v <- a if v == 37}; ok {
     6  	println("37 is found! index =", at)
     7  }
     8  
     9  println("first element of a is:", {v for v <- a})