As far as i understand there are several descriptive concepts to help us analyze the characteristics of a particular melody (such as steps, leaps, melodic contour, disjunct or conjunct motion, for example). In addition, what i gather from cantus firmus there are also several specific prescriptive ideas for writing melodies. Voice leading could perhaps be an another example, but as far as i understand they only apply in the context of chordal harmony.
I use these examples to differentiate from what i'm looking for as i am interested in learning more theories for melodic writing. For instance, a concept (new to me) is the idea that the melodic notes of a single voice carry a specific function similar to the functions of chords in progressions/cadences. If i'm not misunderstanding this idea is a bit different from the other examples above.
Therefore i am interested in additional prescriptive concepts besides cantus firmus for instance. In short, i'd very much appreciate more tips on what to learn.