define-syntax | 易学教程

Error during expansion of macro in Chicken Scheme

阅读更多关于 Error during expansion of macro in Chicken Scheme

问题 I'm learning how the macro system in Scheme works and I'm trying to make my code look more JavaScript-y. So I thought I would start with the function macro. This is how I want a function definition to look: (function id (x) x) It should expand to the following: (define (id x) x) So I write a macro as follows: (define-syntax function (lambda (name args . body) `(define (,name ,@args) ,@body))) However when I use it I get the following error (in Chicken Scheme): Error: during expansion of

Capturing Macros in Scheme

阅读更多关于 Capturing Macros in Scheme

问题 What's the simplest way to define a capturing macro using define-syntax or define-syntax-rule in Racket? As a concrete example, here's the trivial aif in a CL-style macro system. (defmacro aif (test if-true &optional if-false) `(let ((it ,test)) (if it ,if-true ,if-false))) The idea is that it will be bound to the result of test in the if-true and if-false clauses. The naive transliteration (minus optional alternative) is (define-syntax-rule (aif test if-true if-false) (let ((it test)) (if it

how to create a macro in racket where a list becomes the args of said lambda?

阅读更多关于 how to create a macro in racket where a list becomes the args of said lambda?

问题 How would I go about in doing a define-syntax-rule that accepts a list as arguments and a list (or a quote, in case it is a single element) as body of a lambda? i would like to do something like: >(define a (lambdarize '(x y z) '(+ x y z))) #<procedure> >(a 1 2 3) 6 >(define b (lambdarize '(x) 'x)) #<procedure> >(b 1) 1 I have played around with define-syntax-rule and apply , but since lambda itself seems to be a macro and not a procedure, i have been stumped at trying to find it... oh... And

How to control order of Scheme macro expansion?

阅读更多关于 How to control order of Scheme macro expansion?

问题 I'm working with the Racket macro extension syntax-id-rules , that some other Scheme implementations provide under the name identifier-syntax . These let you specify macro expansions that will happen even when the defined identifier isn't in head position. So for example: (define hidden #f) (define-syntax proxy (syntax-id-rules (set!) [(set! proxy v) (set! hidden v)] [proxy hidden])) will set up the identifier proxy to be a proxy for hidden . This is a useless example, but it illustrates the

Scheme Macro for nesting expressions

阅读更多关于 Scheme Macro for nesting expressions

问题 Can a macro be written in Scheme (with define-syntax , for example) which will take expressions like this: (op a b c d e f g h i j) And yield expressions like this as output? (op (op (op (op (op (op (op (op (op a b) c) d) e) f) g) h) i) j) Of course, for arbitrary lengths. I can't think of a way to do it, given some template like this: (define-syntax op (syntax-rules () [(_) 'base-case] [(v1 v2 ...) 'nested-case??])) 回答1: (define bop list) (define-syntax op (syntax-rules () ((op a b) (bop a b

Scheme Macro for nesting expressions

阅读更多关于 Scheme Macro for nesting expressions

Can a macro be written in Scheme (with define-syntax , for example) which will take expressions like this: (op a b c d e f g h i j) And yield expressions like this as output? (op (op (op (op (op (op (op (op (op a b) c) d) e) f) g) h) i) j) Of course, for arbitrary lengths. I can't think of a way to do it, given some template like this: (define-syntax op (syntax-rules () [(_) 'base-case] [(v1 v2 ...) 'nested-case??])) (define bop list) (define-syntax op (syntax-rules () ((op a b) (bop a b)) ((op a b c ...) (op (bop a b) c ...)))) For example, (op 1 2 3 4) expands to (bop (bop (bop 1 2) 3) 4)