2.1 简单数据类型
qinguan
posted @ 2011年7月22日 21:24
in Lisp
, 1095 阅读
——chapter2 Data types
Teach Yourself Scheme in Fixnum Days
布尔类型
Scheme的布尔类型用#t表示true，用#f表示false
> (boolean? #t) #t > (boolean? "fd") #f > (not #f) #t > (not #t) #f > (not 't) #f >
从上面也可以看出，Scheme将所有不是false的值均作为真值。
数字类型
Scheme的数字类型有整型、有理数、实数及复数。
> (number? 42) #t > (number? #t) #f > (complex? 2+3i) #t > (complex? 2) #t > (real? 3.21) #t > (real? 22/7) #t > (rational? 2+3i) #f > (rational? 22/7) #t > (integer? 22/7) #f > (integer? 23) #t >
整型进制表示
> #b1100 =>2进制 12 > #o77 =>8进制 63 > #d12 =>10进制 12 > #x12 =>16进制 18 >
可以用eqv?来判断两个参数是否相等
> (eqv? 42 42) #t > (eqv? 42 #f) #f > (eqv? 42 42.0) #f > (eqv? #b1100 #d12) #t > (eqv? #b1100 #x12) #f > (eqv? #b1100 #xd) #f > (eqv? #b1100 #xc) #t >
如果比较的两个数均为数字，也可以用=
> (= 42 42) #t > (= 42 #f) =: expects type <number> as 2nd argument, given: #f; other arguments were: 42 >
此外，eqv?是严格相等的，包括数据类型，同样是42，如果一个是浮点数，一个是整型，eqv？报false，而=却显示true：
> (= 42 42.0) #t > (eqv? 42 42.0) #f
数字之间的比较还有<, <=, >, >=：
> (< 4 't) <: expects type <real number> as 2nd argument, given: 't; other arguments were: 4 > (< 4 5.6) #t >
对于单个数字参数，-返回参数的相反数，而/返回参数的倒数：
> (- 4) -4 > (/ 4) 1/4 > (/ 0) /: division by zero > (- 0) 0 >
数值中还有max和min过程，要求输入参数类型为实数，max返回输入参数中的最大值，min返回输入数值中的最小值：
> (max 1 2 3 4) 4 > (min 1 2 3 4) 1 > (max #t 2 3 4) max: expects type <real number> as 1st argument, given: #t; other arguments were: 2 3 4 >
abs过程返回参数的绝对值：
> (abs -3.2) 3.2 >
字符类型
Scheme中所有字符类型数据均有前缀#\表示，比如说#\c表示字符c，特殊字符换行用#\newline，tab用#\tab，空格用#\ 或#\space。
字符类型断言用char?：
> (char? #\c) #t > (char? 1) #f > (char? #\;) #t >
字符类型比较用char<?,char=?,char>?:
> (char<? #\a #\b) #t > (char>? #\a #\b) #f > (char=? #\a #\a) #t > (char=? #\a #\A) #f > (char>? #\a #\A) #t >
若大小写不敏感，则用char-ci=?:
> (char-ci=? #\a #\A) #t >
将大写字符转化为小写用char-downcase，相反用char-upcase:
> (char-downcase #\A) #\a > (char-upcase #\a) #\A >
符号类型
该类型用单引号做前缀或标注quote：
> (eqv? (quote E) 'E) #t > (symbol? 'xyz) #t > (symbol? 42) #f >
本书中Scheme 符号类型是大小写不敏感：
Scheme symbols are normally case-insensitive. Thus the symbols Calorie and
calorie are identical:
(eqv? ’Calorie ’calorie)
? #t
但在DrRacket5.1.1中大小写敏感：
> (eqv? (quote E) 'e) #f > (eqv? 'E 'e) #f
可见不同的Scheme实现有差别。
我们可以用define来定义全局变量：
(define size 2) > size 2
>
则size的值就为2。
同时可以用set!来改变这个值：
> (set! size "3") > size "3" >
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