Class: Alf::Types::TupleComputation

Inherits:
Object
  • Object
show all
Defined in:
lib/alf/types/tuple_computation.rb

Overview

Defines the computation of a tuple from expressions mapped to names.

Example:

computation = TupleComputation[
  :big? => lambda{ status > 20 }
  :who  => lambda{ "#{first} #{last}" }
]
computation.call(:last => "Jones", :first => "Bill", :status => 10)
# => {:big? => false, :who => "Bill Jones"}

Instance Method Summary collapse

Instance Method Details

#call(tuple) ⇒ Object Also known as: []

Makes the computation in the context of a tuple

This is a convenient method for the following, longer expression:

evaluate(TupleScope.new(tuple))

Note, however, using a scope as in the example above is much more efficient when evaluating the same computation on multiple tuples in sequence.

Parameters:

  • tuple (Hash) —

    a Tuple instance

Returns:

  • (Object) —

    the resulting tuple



47
48
49
 
# File 'lib/alf/types/tuple_computation.rb', line 47

def call(tuple)
  evaluate(Support::TupleScope.new(tuple))
end

#evaluate(scope = nil) ⇒ Hash

Computes the resulting tuple when expressions are evaluated in the context of scope

Parameters:

  • scope (TupleScope) (defaults to: nil) —

    a tuple scope instance.

Returns:

  • (Hash) —

    the resulting tuple



57
58
59
 
# File 'lib/alf/types/tuple_computation.rb', line 57

def evaluate(scope = nil)
  hmap{|_,v| v.is_a?(TupleExpression) ? v.evaluate(scope) : v }
end

#project(attributes, allbut = false) ⇒ Object

Projects this tuple computation on specified attribute names.

Parameters:

  • attributes (AttrList) —

    some attribute names.

  • allbut (Boolean) (defaults to: false) —

    apply a allbut projection?



65
66
67
68
 
# File 'lib/alf/types/tuple_computation.rb', line 65

def project(attributes, allbut = false)
  TupleComputation.new\
    AttrList.coerce(attributes).project_tuple(reused_instance, allbut)
end

#to_attr_list ⇒ AttrList

Converts to an attribute list.

Returns:

  • (AttrList) —

    a list of computed attribute names



85
86
87
 
# File 'lib/alf/types/tuple_computation.rb', line 85

def to_attr_list
  AttrList.new(reused_instance.keys)
end

#to_heading ⇒ AttrList

Converts to a heading.

Returns:

  • (AttrList) —

    a computed heading from static analysis of expressions



78
79
80
 
# File 'lib/alf/types/tuple_computation.rb', line 78

def to_heading
  Heading.new hmap{|_,v| v.is_a?(TupleExpression) ? v.infer_type : v.class}
end

#to_lispy ⇒ String

Returns a lispy expression.

Returns:

  • (String) —

    a lispy expression for this tuple computation



92
93
94
 
# File 'lib/alf/types/tuple_computation.rb', line 92

def to_lispy
  "{" << map{|k,v| "#{k}: #{Support.to_lispy(v)}" }.join(', ') << "}"
end

#to_ruby_literal ⇒ String Also known as: inspect, to_s

Returns a ruby literal for this expression.

Returns:

  • (String) —

    a literal s.t. ‘eval(self.to_ruby_literal) == self`



99
100
101
 
# File 'lib/alf/types/tuple_computation.rb', line 99

def to_ruby_literal
  "Alf::TupleComputation[#{to_lispy[1...-1]}]"
end

#to_tuple_computation ⇒ Object

Returns self



71
72
73
 
# File 'lib/alf/types/tuple_computation.rb', line 71

def to_tuple_computation
  self
end