Input:
// LGSL version of C2E1v_green from "The Cg Tutorial" (Addison-Wesley, ISBN
// 0321194969) by Randima Fernando and Mark J. Kilgard.  See page 38.

float3 C2E1v_green(in float2 position : ATTRIBUTE_0, out float4 NDCPosition : HPOS) : INTERPOLATOR_0
{
  NDCPosition = float4(position,0,1);
  return float3(0,1,0);
}

------------------------------------------
Output:

layout(location = 0) out vec3 return_value_INTERPOLATOR_0;
layout(location = 0) in vec2 position;

void main()
{

  gl_Position = vec4(position,0,1);
  return_value_INTERPOLATOR_0 =  vec3(0,1,0);
}