Records and lists: build structured data

Basic types describe individual values. A record bundles named fields into one structured item. A list gathers a sequence of items. Combining them lets you describe a whole dataset and its nested parts.

A record gives every field a name and a type #

Related language terms include struct and tuple, but their exact rules differ by language. Here, use “record” for a bundle of named fields. Different fields may have different types; the three subject-mark fields happen to share one type.

WordInPara is another record #

X.word selects the word field of record X. It is not the entire record. A paragraph list contains many such records, including separate entries for repeated word occurrences.

A list is an ordered sequence #

MarksCardList is a list of MarksCard records. ParagraphWordList is a list of WordInPara records. ShoppingBillList is a list of ShoppingBill records. Lists can have different lengths, can be empty, and can contain repeated values. The course mainly uses lists whose elements share one declared type.

Order matters when reconstructing a paragraph or interpreting word positions. A count or sum over unchanged records is order-independent, but that does not mean list order is irrelevant to every task.

Nested records and lists in a bill #

To check whether a bill has only food, inspect the category field of every Item in its items list. To count shopping visits, iterate over the outer ShoppingBillList. The level you iterate over decides whether you count bills or item rows.

Field types are only part of data sanity #

A record can have individually valid field types and still have a wrong total, duplicate ID or incorrect category. You also need cross-field constraints such as totalMarks = maths + physics + chemistry, and across-record checks such as ID uniqueness. This distinction matters when turning a diagram into an actual validation procedure.

Source: Lecture 1.10 — Introduction to complex datatypes. Small teaching datasets and diagrams are prepared for these notes; lecture and tutorial totals are identified explicitly.