Often, the Kolmogorov complexity of some string $x$ is defined as the length of the shortest program producing $x$, for example on wikipedia.
So to give this more formal meaning, define $$ K'(x) := |f| + |a_1| + \ldots |a_k| $$ where $f(s_1, s_2,\ldots, s_k)$ is some function with $k$ arguments in some specific programming language (like C++ for example).
How does this definition relates to Kolmogorov complexity? I mean this could not be the same, as with this definition we have $$ K'(xy) \le K'(x) + K'(y) + C $$ with some constant $C$. For if $f(a_1, \ldots, a_k) = x$ and $g(b_1,\ldots, b_l) = y$ are functions to compute $x$ and $y$, then
return concat(f(a1, ..., ak), g(b1,...,bl));
would be a function to compute $xy$ of complexity $|f| + |a1| + \ldots + |ak| + |g| + |b1| + \ldots |bl| + C$, where $C$ represents the bits needed to declare $h$, the parentheses, the return statement and to call concat (string concatentation function).
Hence $K'(xy) \le K'(x) + K'(y) + C$.
But as is well-know for the usual Kolmogorov complexity we do not have such an subadditivity?
EDIT: This will also work if we just allow functions with a single parameter.