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20 Overview of the Guile API

Guile's application programming interface (API) makes functionality available that an application developer can use in either C or Scheme programming. The interface consists of elements that may be macros, functions or variables in C, and procedures, variables, syntax or other types of object in Scheme. Broadly speaking, the interface as a whole can be divided into three groups.

  1. Elements that are available equivalently as C functions or Scheme procedures.
  2. Elements that are only available as macros, functions or variables for C programming.
  3. Elements that are only available as procedures or other objects in Scheme.

Functions/procedures in the first group are often known as primitives, subrs or builtins. An example is the assq Scheme procedure, which is also available as scm_assq in C.

Elements in the second and third groups exist because they provide additional language-specific benefits in either Scheme or C. Examples are the C macro SCM_CONSP, which is faster and more convenient in C programming than the primitive scm_pair_p, and the procedure-with-setter make-object-property, which provides a more convenient property handling interface in Scheme than the primitives on which it is based.