25. Bigloo The Programming Language (4.6a) User manual for version 4.6a January 2025 -- Macro expansion

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Macro expansion
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| Bigloo makes use of two macro expansion system. The one based on the expansion passing style [Dybvig et al. 86] and the one advocated by the R5RS, for which see http://www-sop.inria.fr/indes/fp/Bigloo/doc/r5rs.html.
### 25.1 Expansion passing style macros
define-expander name proc | bigloo syntax
This form defines an expander, `name`, where `proc` is a procedure of two arguments: a form to macro-expand, and an expander.
define-macro (name [args]...) body | bigloo syntax
This form is itself macro-expanded into a `define-expander` form. Macro expanders cannot be exported or imported since there is no way to specify expanders in a module declaration. Macros defined with `define-expander` and `define-macro` are used by both the compiler and the interpreter.
Here is an example of an expander:
    (define-expander when
       (lambda (x e)
          (match-case x
             ((?- ?test . ?exps)
              (e `(if ,test (begin ,@exps)) e))
             (else
               (error "when" "illegal form" x)))))

    (when (> a 0) (print a) a)
       ==> (if (> a 0) (begin (print a) a))
The same example can written with a `define-macro` form:
    (define-macro (when test . exps)
       `(if ,test (begin ,@exps)))
### 25.2 Revised(5) macro expansion
Bigloo support the Revised(5) Report on the Scheme programming language. For a detailed documentation see See r5rs, Expressions.
let-syntax (binding...) body | syntax
letrec-syntax (binding...) body | syntax
define-syntax keyword transformer | syntax
syntax-rules literals rule... | syntax
These three forms are compatible with the description of the Revised(5) Report on the Algorithmic Language Scheme. Implementation Note: Current Bigloo does not ensure hygiene for `let-syntax` and `letrec-syntax`. Hygienic expansion is only guaranteed for `define-syntax`.

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Last update Mon Jan 27 07:55:49 2025.