Builtinform

Builtinform is a concept used to describe language constructs that are implemented directly by a language’s runtime, rather than defined as user-written functions. In many Lisp-family languages, such constructs are referred to as special forms. A builtinform determines how its arguments are evaluated, how variables are bound, and how control flows within a program.

Semantics and role

A builtinform typically specifies a distinct evaluation strategy. It may cause only certain arguments to be evaluated, enforce a particular evaluation order, or establish a lexical binding before evaluating a body. Examples commonly cited in discussions of Lisp-like languages include conditional forms, quotation, and binding forms. In Scheme and related dialects, forms such as if, quote, define, lambda, and begin (or let in some variants) are treated as builtinforms.

Implementation and usage

In interpreters, builtinforms are usually dispatch targets with dedicated evaluation paths or opcodes. This specialization allows control flow, scoping, and other semantics to be implemented efficiently and consistently, without requiring a function call to execute. Builtinforms differ from regular functions in that their argument handling and evaluation rules are intrinsic to the language’s core semantics.

Relation to macros

Builtinforms are distinct from macros. Macros operate on source code prior to evaluation, expanding or transforming code, whereas builtinforms are evaluated directly by the runtime according to the language’s evaluation rules.

Notes

The exact set of builtinforms and their behavior vary across languages and versions. The term is sometimes used interchangeably with “special forms,” though some environments differentiate between primitive syntactic forms and other intrinsic constructs. Related concepts include special forms, macros, and intrinsic operators.