Error: cannot evaluate at compile time: col

# Using the col constant breaks the compilation.
var a = @[("asdf", 1323.3434), ("bleh", 123.456), ("meh", -32444.232)]
let col = 1 # column I want
var r = @[a[0][col]]
for i in 1..len(a)-1:
  r.add(a[i][col])
echo(r)

# but hardcoding it works:
var a = @[("asdf", 1323.3434), ("bleh", 123.456), ("meh", -32444.232)]
var r = @[a[0][1]]
for i in 1..len(a)-1:
  r.add(a[i][1])
echo(r)