嵌套表达式的方案宏

问题描述

是否可以在Scheme中编写宏(例如，使用define-syntax)，该宏将采用以下表达式:

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)

并将这样的表达式作为输出吗?

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) 

当然，对于任意长度.给定这样的模板，我想不出一种方法:

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??]))

推荐答案

(define bop list)

(define-syntax op
  (syntax-rules ()
    ((op a b) (bop a b))
    ((op a b c ...) (op (bop a b) c ...))))

例如，(op 1 2 3 4)扩展为(bop (bop (bop 1 2) 3) 4)并计算为(((1 2) 3) 4).

For example, (op 1 2 3 4) expands to (bop (bop (bop 1 2) 3) 4) and evaluates to (((1 2) 3) 4).

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