Our declarative modeling language Rel now supports modules!

A module groups together one or more declarations. For instance

module person
def name = "Sherlock Holmes"
module address
def street = "221B Baker Street"
def city = "London"
def country = "UK"
end
def telephone = "+44 202-456-1111"
end

This will display as below:

def output = person[:address][:street]

Relation: "221B Baker Street"

Modules can be imported into a lexical scope using the with construct, allowing the use of short names. The with construct can also be used to rename imported members.

with person use name, telephone as phone
with person:address use street
def output = name
def output = phone
def output = street

Relation:

module person
def name = "Sherlock Holmes"
module address
def street = "221B Baker Street"
def city = "London"
def country = "UK"
end
def telephone = "+44 202-456-1111"
end
with person use name, telephone as phone
with person:address use street
def output = name
def output = phone
def output = street

Modules are relations and computations can be performed over them like any other relation:

def person_without_phone(key, values...) =
person(key, values...) and
key != :telephone
def output = json_string[person_without_phone]

Relation:

" { "address": { "city": "London", "country": "UK", "street": "221B Baker Street" }, "name": "Sherlock Holmes" }"

For a more detailed introduction to modules, see the documentation.