(program	
 (fun foo
  [(:= v1 float3) 
   (:= v2 float3)])

 (fun foo
  [(:= v1 float2) 
   (:= v2 float2) 
   (:= v3 float2)])

 (fun vertex vs_main
  [] 
  (:= v float 2) 
  (foo v v)))