### Compilation failed:

error: 3: 'main' must return: 'vec4', 'float4', or 'half4'
void main() {
^^^^^^^^^^^
error: 4: unknown identifier 'sk_FragColor'
    sk_FragColor.x = half(packHalf2x16(a));
    ^^^^^^^^^^^^
error: 4: unknown identifier 'packHalf2x16'
    sk_FragColor.x = half(packHalf2x16(a));
                          ^^^^^^^^^^^^
error: 5: unknown identifier 'sk_FragColor'
    sk_FragColor.x = half(packUnorm2x16(a));
    ^^^^^^^^^^^^
error: 6: unknown identifier 'sk_FragColor'
    sk_FragColor.x = half(packSnorm2x16(a));
    ^^^^^^^^^^^^
error: 6: unknown identifier 'packSnorm2x16'
    sk_FragColor.x = half(packSnorm2x16(a));
                          ^^^^^^^^^^^^^
error: 7: unknown identifier 'sk_FragColor'
    sk_FragColor.x = half(packUnorm4x8(b));
    ^^^^^^^^^^^^
error: 7: unknown identifier 'packUnorm4x8'
    sk_FragColor.x = half(packUnorm4x8(b));
                          ^^^^^^^^^^^^
error: 8: unknown identifier 'sk_FragColor'
    sk_FragColor.x = half(packSnorm4x8(b));
    ^^^^^^^^^^^^
error: 8: unknown identifier 'packSnorm4x8'
    sk_FragColor.x = half(packSnorm4x8(b));
                          ^^^^^^^^^^^^
10 errors