Map Comprehension

rascal-0.40.17

Synopsis

A map comprehension generates a map value.

Syntax

( Exp₁ : Exp₂ | Gen₁, Gen₂, ... )

Types

Exp₁	Exp₂	( Exp₁ : Exp₂ \| Gen₁, Gen₂, ... )
T₁	T₂	map[T₁, T₂]

Description

A map comprehension consists of a number of two contributing expressions Exp₁ (for key values), and Exp₂ (the values associated with those key values) and a number of generators Gen₁, Gen₂, Gen₃, ... that are evaluated as described in Comprehensions.

Examples

Introduce a map of fruits:

rascal>fruits = ("pear" : 1, "apple" : 3, "banana" : 0, "berry" : 25, "orange": 35);
map[str, int]: ("banana":0,"pear":1,"orange":35,"berry":25,"apple":3)
rascal>import String;
ok

Use a map comprehension to filter fruits with a name of at most 5 characters:

rascal>(fruit : fruits[fruit] | fruit <- fruits, size(fruit) <= 5);
map[str, int]: ("pear":1,"berry":25,"apple":3)

Use a map comprehension to filter fruits with an associated value larger than 10:

rascal>(fruit : fruits[fruit] | fruit <- fruits, fruits[fruit] > 10);
map[str, int]: ("orange":35,"berry":25)