# Main Command: Go
# Ulam Spiral by Guy Walker
# www.logoarts.co.uk

To New
  # set default screen, pen and turtle
  ResetAll SetScreenSize [400 400] HideTurtle
  SetSC Black SetPC Green SetPS 1 PenUp
End

To DrawSpiral
  # draw spiral of 361 square dots from centre 
  For [N 1 19 0.5] [
    Repeat Integer :N [
      Make "Count :Count+1
      If Member? :Count :Primes [SetPC Yellow] [SetPC [0 63 0] ]
      Dot Pos Forward 20 Wait 3]
    Left 90] 
End

To Init 
  Make "Count 0
  Make "Primes [2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 101 103 107 109 113 127 131 137 139 149 151 157 163 167 173 179 181 191 193 197 199 211 223 227 229 233 239 241 251 257 263 269 271 277 281 283 293 307 311 313 317 331 337 347 349 353 359]
End

To Go
  New SetPS 0 SetPW 11 SetH 90 
  Init DrawSpiral
End