### Compilation failed:

error: 3: 'main' must return: 'vec4', 'float4', or 'half4'
void main() {
^^^^^^^^^^^
error: 4: unknown identifier 'sk_FragColor'
    if (unknownInput > 5) { sk_FragColor = half4(0.75); } else { discard; }
                            ^^^^^^^^^^^^
error: 4: discard statement is only permitted in fragment shaders
    if (unknownInput > 5) { sk_FragColor = half4(0.75); } else { discard; }
                                                                 ^^^^^^^
error: 6: unknown identifier 'sk_FragColor'
    while (i < 10) { sk_FragColor *= 0.5; i++; }
                     ^^^^^^^^^^^^
error: 7: unknown identifier 'sk_FragColor'
    do { sk_FragColor += 0.25; } while (sk_FragColor.x < 0.75);
         ^^^^^^^^^^^^
error: 7: unknown identifier 'sk_FragColor'
    do { sk_FragColor += 0.25; } while (sk_FragColor.x < 0.75);
                                        ^^^^^^^^^^^^
6 errors