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How to get all keys from a Rascal map?

Suppose I have a map like so:

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

Is there any way to return all the keys in the map, i.e. "apple", "pear", "banana", "kiwi"? From the documentation at http://tutor.rascal-mpl.org/Rascal/Expressions/Values/Map/Comprehension/Comprehension.html#/Rascal/Expressions/Values/Map/Map.html , it does not seem like there's a built in way. Is it possible?

Solution

  • A number of ways:

    First is just projecting out the first column:

    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"}

    Second is labeling the columns, and doing the same (either the <> notation or the . notation)

    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"}

    Finally maps are also generators for their own keys, as in:

    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