如何从流氓地图中获取所有键？

Question

假设我有一张这样的地图：

map[str,int] a = ("apple": 1, "pear": 2, "banana": 3, "kiwi": 4); 

有没有办法返回地图中的所有键，即“apple”、“pear”、“banana”、“kiwi”？从 http://tutor.rascal-mpl.org/Rascal/Expressions/Values/Map/Comprehension/Comprehension.html#/Rascal/Expressions/Values/Map/Map.html 的文档来看，似乎没有内置方式。有可能吗？

Answer 1

多种方式：

First 只是突出第一列：

rascal>map[str,int] a = ("apple": 1, "pear": 2, "banana": 3, "kiwi": 4); 
map[str, int]: ("banana":3,"pear":2,"kiwi":4,"apple":1)
rascal>a<0>
set[str]: {"banana","pear","kiwi","apple"} 

其次是标记列，并做同样的事情（<> 表示法或 . 表示法）

rascal>map[str fruit, int count] b = ("apple": 1, "pear": 2, "banana": 3, "kiwi": 4); 
map[str fruit, int count]: ("banana":3,"pear":2,"kiwi":4,"apple":1)
rascal>b<fruit>
set[str]: {"banana","pear","kiwi","apple"}
rascal>b.fruit
set[str]: {"banana","pear","kiwi","apple"}

最后，地图也是它们自己的键的生成器，如下所示：

rascal>[ f | f <- a]
list[str]: ["banana","pear","kiwi","apple"]
rascal>{ f | f <- a}
set[str]: {"banana","pear","kiwi","apple"}
rascal>import IO;
rascal>for (f <- a)
>>>>>>>  println(f);
banana
pear
kiwi
apple