SQL & PL/SQL

I have a multi-part polyline in a row in an Oracle 18c table. The polyline's geometry information is stored in a SHAPE column; the datatype is a user-defined spatial type called SDE.ST_Geometry.
I've written a PL/SQL function call m_as_length() that replaces a coordinate in the polyline's vertices with the cumulative length of the line. The coordinate is called an "M" coordinate (aka a "Measure-value"). M coordinates are similar to X and Y coordinates, but are used for specialized linear referencing purposes.

Input:
MULTILINESTRING M (( 0.0 5.0 -100000.0, 10.0 10.0 -100000.0, 30.0 0.0 -100000.0),( 50.0 10.0 -100000.0, 60.0 10.0 -100000.0))
--select sde.st_astext(shape) from polylines

Output:
MULTILINESTRING M ((0 5 0, 10 10 11.18, 30 0 33.54),(50 10 33.54, 60 10 43.54))
--select m_as_length(shape) from polylines

Question:
I'm a novice when it comes to PL/SQL. Can the m_as_length() function be improved?

with
    function pythagoras(x1 in number, y1 in number, x2 in number, y2 in number) return number is
    begin
        return round(  sqrt(power(x2 - x1, 2) + power(y2 - y1, 2))  ,2);
    end;
   
    function m_as_length(shape in sde.st_geometry) return varchar2
    is
        result              varchar2(32767);
        vertex              varchar2(32767);
        vertex_set          varchar2(32767);
        i                   number;
        j                   number;
        num_parts           number;
        num_points          number;
        oldX                number;
        oldY                number;
        newX                number;
        newY                number;
        line_len            number;
    begin
        num_parts           := sde.st_geometry_operators.st_numgeometries_f(shape); 
        oldX                := sde.st_geometry_operators.st_x_f(sde.st_geometry_operators.st_startpoint_f(sde.st_geometry_operators.st_geometryN_f(shape,1)));
        oldY                := sde.st_geometry_operators.st_y_f(sde.st_geometry_operators.st_startpoint_f(sde.st_geometry_operators.st_geometryN_f(shape,1)));
        line_len            := 0;
       
        for i in 1..num_parts
        loop
            num_points      := sde.st_geometry_operators.st_numpoints_f(sde.st_geometry_operators.ST_GeometryN_f(shape,i));
            vertex_set      := null;
            for j in 1..num_points
            loop
                newX        := sde.st_geometry_operators.st_x_f(sde.st_geometry_operators.st_pointn_f(sde.st_geometry_operators.st_geometryn_f(shape,i),j));
                newY        := sde.st_geometry_operators.st_y_f(sde.st_geometry_operators.st_pointn_f(sde.st_geometry_operators.st_geometryn_f(shape,i),j));
                if j <> 1 then
                   line_len := line_len + pythagoras(oldX, oldY, newX, newY);
                end if;
                oldX        := newX;
                oldY        := newY;
                vertex      := newX || ' ' || newY || ' ' || line_len;
                vertex_set  := vertex_set || vertex || ', ';
            end loop;
            vertex_set      := '(' || rtrim((vertex_set),', ') || '),';
            result          := result || vertex_set;
        end loop;
        result              := 'MULTILINESTRING M (' || rtrim((result),',') || ')';
        return result;
    end;
select
    m_as_length(shape)
from
    polylines

Related:
Use SDE.ST_GEOMETRY functions in a custom function
Explains why the function calls are so verbose: sde.st_geometry_operators.st_numgeometries_f.
ST_GEOMETRY functions (links):
st_numgeometries
st_x
st_startpoint
st_geometryN
st_numpoints
st_pointn
I have a JavaScript expression that serves the same purpose (different use case). It's easier to read than the PL/SQL function.