2016-06-12_18-15-34.lua

local function isByte( n )
	return type( n ) == "number" and n >= 0 and n < 256
end

types.define( "byte", { type = "custom", value = isByte } )
types.define( "optional byte", "byte | nil" )
types.define( "colour", "{ byte, byte, byte, optional byte }" )

print( types.check( { 1, 2 }, "colour" ) ) --> false
print( types.check( { 1, 2, 3 }, "colour" ) ) --> true
print( types.check( { 1, 2, 3, 4 }, "colour" ) ) --> true
print( types.check( { 1, 2, 3, 4, 5 }, "colour" ) ) --> false
print( types.check( { 6127, 32189, 412 }, "colour" ) ) --> false