DataFrames transform list comprehension

julia> using DataFrames, ShiftedArrays

julia> df = DataFrame(ret = rand(100));

julia> transform!(df, ["ret" => (col -> lag(col, i)) => "lag$i" for i ∈ 1:3])
100×4 DataFrame
 Row │ ret        lag1             lag2             lag3            
     │ Float64    Float64?         Float64?         Float64?        
─────┼──────────────────────────────────────────────────────────────
   1 │ 0.624376   missing          missing          missing         
   2 │ 0.605845         0.624376   missing          missing         
   3 │ 0.0379192        0.605845         0.624376   missing         
   4 │ 0.759851         0.0379192        0.605845         0.624376
   5 │ 0.32622          0.759851         0.0379192        0.605845