How to create user-defined data types in ALGOL?

In ALGOL, one of the earliest high-level programming languages that was significantly influential in the development of many other languages, user-defined data types are slightly different than coding languages in common use today like C++ or Java. However, it's completely doable.

To create user-defined data types in ALGOL, one typically employs array structures. Here is how you can do it:

Step 1: Define The Array Structures

You need to start by defining the array structures. In ALGOL, array structures are highly flexible and allow for an elaborate level of defining data organization. Here's an example of how you can define a composite data type using arrays:

INTEGER ARRAY A[0:5];

REAL ARRAY B[1:10];

In the above example, 'A' is an integer array with six elements, and 'B' is a real number array with ten elements.

Step 2: Employing Structures And Referencing

Once the array structure has been defined, it can be coupled with switch structures for added flexibility. A switch in ALGOL is a user-defined data type that can act as a reference to other variables or constants. To create a switch as a reference to an array, you can do this:

SWITCH X = A[2];

In the above example, 'X' is a switch referencing the 2nd element of array 'A'.

Step 3: Accessing of Data

In ALGOL, the real value of user-defined data types comes in how data is accessed. By defining data based on user needs, data can be fetched in ways that are powerful. For example, you can set the value for the 2nd element of array 'A' as:

INTO :X: 5;

In the above case, because 'X' is a switch that references the 2nd element of array 'A', setting a value to 'X' is the same as setting a value for the 2nd element of 'A'.

In sum, user-defined data types in ALGOL are primarily defined using array structures, and then employed through structures and references, facilitating powerful control on data access and manipulation based on user needs. Remember that this high-level coding was primarily developed in the late 1950s and thus varies significantly from modern programming languages. With this understanding, it becomes easier to scale through the complexity and achieve meaningful results with ALGOL.