我在 Lisp 中弄湿了我的脚，defpackage并开始了一个可耻的开始，即一个我无法开始理解的错误。
下面的代码是尝试创建一种子语言来对向量执行中缀操作。我想将它用于涉及一些线性代数的项目。
我的代码的“肉”是parse-infix. 此函数找到具有最高优先级的运算符，调用apply-op以替换所述运算符及其操作数，operator (operand, operand)从而缩小列表，并迭代直到列表仅包含结果。支持的运算符有四个规则、相等（将结果绑定到 Lisp 符号）和向量连接。
这是代码，疣和所有内容：
(defpackage :infix
(:use :common-lisp)
(:export operator-list
operators
parse-infix
infix))
(in-package :infix)
(defun parse-input (a)
"Turns symbols into numbers as necessary while reading an expression"
(if (symbolp a) (symbol-value a) a))
;; Definition of structure containing data for one operator
(defmacro mapf (op type)
""
`(lambda (a b)
(map ,type #'(lambda (x y)
(funcall ,op x y)) (parse-input a) (parse-input b))))
(defstruct (operator
(:conc-name op-)
(:constructor op (sym &key (func (mapf sym 'vector)) priority associativity n-operands)))
sym ; Operator symbol
func ; Function to be applied to operands
priority ; Other operators attributes
(associativity 'left-to-right) ; Evaluation order for operators
; that appear more than once in a row
(n-operands 2)) ; Number of operands (NOT IMPLEMENTED)
(defmacro operator-list (&body ops)
"Produces an operator list from a list of operator structs."
`(mapcar #'(lambda (y) (apply #'op
(mapcar #'(lambda (x) (if (listp x) (eval x) x)) y))) ',ops))
(defparameter operators
(operator-list
(+ :priority 4)
(- :priority 4)
(* :priority 3)
(/ :priority 3)
(^ :priority 2 :func expt :associativity right-to-left)
(& :priority 2 :func (lambda (x y) (concatenate 'vector x y)))
(= :priority 10 :func (lambda (x y) (set (intern (string x)) y))))
"Default set of operators, which perform arithmetic operations on
vectors lengthwise. If one vector is shorter than the other, the result
is truncated.")
(defun apply-op (b)
"Reads a segment of a list of the format operand/operator/operand (in 3 consecutive
cells) and leaves operator (operand, operand) in a single cell."
(setf (car b) (funcall (op-func (caadr b))
(car b)
(caddr b))
(cdr b) (cdddr b)))
(defun parse-infix (b &key (operator-list operators))
"Parses an infix expression by calling apply-op repeatedly until the entire
expression is processed."
(let ((expr (mapcar #'(lambda (x)
(case (type-of x)
(symbol (or (member x operator-list :key #'op-sym) x))
(cons (parse-infix x))
(otherwise x))) b)))
(loop while (cdr expr) do
(apply-op (reduce #'(lambda (x y &aux (op1 (caadr x)) (op2 (caadr y)))
(if (or (< (op-priority op2) (op-priority op1))
(and (= (op-priority op1) (op-priority op2))
(eq (op-associativity op1) 'right-to-left))) y x))
(remove-if #'listp (mapcon #'list expr) :key #'caddr)))
finally (return (car expr)))))
(defmacro infix (&rest b)
"Wrapper to create lists for parse-infix"
`(parse-infix ',b))
这是障碍。这些功能似乎正在工作......
? (infix (#(2 3) + #(4 5)) * #(2 2))
#(12 16)
? (infix (#(100) & (#(2 3) + #(4 5)) * #(2 2))) ; '& is concatenation
#(200 12)
? (infix A = #(5 5) + #(10 10))
#(15 15)
? A
#(15 15)
...但是当我离开包时，连接（&）运算符突然“死”：
? (in-package :cl-user)
#<Package "COMMON-LISP-USER">
? (infix:infix A = #(5 5) + #(10 10))
#(15 15)
? (infix:infix (#(2 3) + #(4 5)) * #(2 2))
#(12 16)
? (infix:infix (#(100) & (#(2 3) + #(4 5)) * #(2 2)))
> Error: The value & is not of the expected type LIST.
> While executing: (:INTERNAL INFIX:PARSE-INFIX), in process listener(1).
> Type :POP to abort, :R for a list of available restarts.
> Type :? for other options.
1 >
我试图跟踪包的功能并注意到，无论出于何种原因，当我离开infix包时，'& 不再被识别为运算符。我不知道为什么会这样。任何输入表示赞赏。
PS。许多人可能已经注意到，这一切都在 Clozure Common Lisp 中。