6.6.15 Record Overview

Records, also called structures, are Scheme’s primary mechanism to define new disjoint types. A record type defines a list of fields that instances of the type consist of. This is like C’s struct.

Historically, Guile has offered several different ways to define record types and to create records, offering different features, and making different trade-offs. Over the years, each “standard” has also come with its own new record interface, leading to a maze of record APIs.

At the highest level is SRFI-9, a high-level record interface implemented by most Scheme implementations (see SRFI-9 Records). It defines a simple and efficient syntactic abstraction of record types and their associated type predicate, fields, and field accessors. SRFI-9 is suitable for most uses, and this is the recommended way to create record types in Guile. Similar high-level record APIs include SRFI-35 (see SRFI-35) and R6RS records (see rnrs records syntactic).

Then comes Guile’s historical “records” API (see Records). Record types defined this way are first-class objects. Introspection facilities are available, allowing users to query the list of fields or the value of a specific field at run-time, without prior knowledge of the type.

Finally, the common denominator of these interfaces is Guile’s structure API (see Structures). Guile’s structures are the low-level building block for all other record APIs. Application writers will normally not need to use it.

Records created with these APIs may all be pattern-matched using Guile’s standard pattern matcher (see Pattern Matching).