列表操作

函数	类型签名	说明	例子
head	[a] -> a	取列表第一个元素	head [1,2,3] = 1
tail	[a] -> [a]	去掉列表第一个元素	tail [1,2,3] = [2,3]
init	[a] -> [a]	去掉列表最后一个元素	init [1,2,3] = [1,2]
last	[a] -> a	取列表最后一个元素	last [1,2,3] = 3
length	[a] -> Int	计算列表长度	length [1,2,3] = 3
null	[a] -> Bool	判断列表是否为空	null [] = True
reverse	[a] -> [a]	翻转列表	reverse [1,2,3] = [3,2,1]
take	Int -> [a] -> [a]	取前 n 个元素	take 2 [1,2,3] = [1,2]
drop	Int -> [a] -> [a]	丢弃前 n 个元素	drop 2 [1,2,3] = [3]
splitAt	Int -> [a] -> ([a],[a])	分割列表为两部分	splitAt 2 [1,2,3] = ([1,2],[3])
filter	(a -> Bool) -> [a] -> [a]	过滤满足条件的元素	filter even [1..5] = [2,4]
map	(a -> b) -> [a] -> [b]	对列表每个元素应用函数	map (+1) [1,2,3] = [2,3,4]
foldl	(b -> a -> b) -> b -> [a] -> b	从左到右折叠	foldl (+) 0 [1,2,3] = 6
foldr	(a -> b -> b) -> b -> [a] -> b	从右到左折叠	foldr (:) [] [1,2,3] = [1,2,3]
zip	[a] -> [b] -> [(a,b)]	两个列表配对成元组列表	zip [1,2] ['a','b'] = [(1,'a'),(2,'b')]
zipWith	(a -> b -> c) -> [a] -> [b] -> [c]	两个列表的对应元素分别应用一个函数，返回一个新列表	zipWith (+) [1,2] [3,4] = [4,6]
concat	[[a]] -> [a]	合并列表的列表	concat [[1,2],[3]] = [1,2,3]
concatMap	(a -> [b]) -> [a] -> [b]	对列表每个元素应用函数，返回一个新列表	concatMap (\x -> [x,x]) [1,2,3] = [1,1,2,2,3,3]
elem	Eq a => a -> [a] -> Bool	判断元素是否在列表中	elem 3 [1,2,3] = True
notElem	Eq a => a -> [a] -> Bool	判断元素不在列表中	notElem 4 [1,2,3] = True
takeWhile	(a -> Bool) -> [a] -> [a]	从头取满足条件的元素	takeWhile (<3) [1,2,3] = [1,2]
dropWhile	(a -> Bool) -> [a] -> [a]	从头丢弃满足条件的元素	dropWhile (<3) [1,2,3] = [3]
span	(a -> Bool) -> [a] -> ([a], [a])	从头分割列表，前部分满足条件，后部分不满足，在第一次不满足条件时停止	span (<3) [1,2,3] = ([1,2],[3])
all	(a -> Bool) -> [a] -> Bool	判断列表所有元素是否满足条件	all (<3) [1,2,3] = True
\\	(a -> Bool) -> [a] -> [a]	列表差集操作符	[1,2,3] \\ [1,2] = [3]
flip	(a -> b -> c) -> b -> a -> c	翻转函数参数顺序	flip (++) "word" " hello" = "hello word"

命令	作用
help(Name)	查看某个谓词的用法简要说明
apropos(Keyword)	搜索包含某关键词的所有文档条目
listing(Name/Arity)	查看用户自定义谓词定义
predicate_property(P,Prop)	查询谓词的属性
current_predicate(Name/Arity)	查看所有当前存在的谓词
trace. / notrace.	启用/禁用调试

• Contents are from Haskell Notes

Table of Contents generated with DocToc

• Contents are from Prolog Notes

Table of Contents generated with DocToc