Class: PatternMatching

Inherits:
Object show all
Defined in:
opal/opal/corelib/pattern_matching.rb

Overview

A "userland" implementation of pattern matching for Opal

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(from, pattern) ⇒ PatternMatching

Returns a new instance of PatternMatching.


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# File 'opal/opal/corelib/pattern_matching.rb', line 10

def initialize(from, pattern)
  @from, @pattern = from, pattern
  @returns = []
end

Instance Attribute Details

#returnsObject (readonly)

Returns the value of attribute returns.


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# File 'opal/opal/corelib/pattern_matching.rb', line 15

def returns
  @returns
end

Class Method Details

.call(from, pattern) ⇒ Object


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# File 'opal/opal/corelib/pattern_matching.rb', line 4

def self.call(from, pattern)
  pm = new(from, pattern)
  pm.match || (return nil)
  pm.returns
end

Instance Method Details

#match(from = @from, pattern = @pattern) ⇒ Object


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# File 'opal/opal/corelib/pattern_matching.rb', line 17

def match(from = @from, pattern = @pattern)
  if pattern == :var
    @returns << from
    true
  else # Pattern is otherwise an Array
    type, *args = *pattern

    case type
    when :save # from =>
      @returns << from
      match(from, args[0])
    when :lit # 3, 4, :a, (1..), ... (but also ^a)
      args[0] === from
    when :any # a | b
      args.any? { |arg| match(from, arg) }
    when :all # Array(1) which works as Array & [1] (& doesn't exist though...)
      args.all? { |arg| match(from, arg) }
    when :array # [...]
      fixed_size, array_size, array_match = *args
      return false unless from.respond_to? :deconstruct
      a = from.deconstruct
      return false if fixed_size && a.length != array_size
      return false if a.length < array_size

      skip_elems = 0
      skip_rests = 0

      array_match.each_with_index.all? do |elem, i|
        type, *args = elem
        case type
        when :rest
          skip_elems = a.size - array_size
          skip_rests = 1
          match(a[i...i + skip_elems], args[0]) if args[0] # :save?
          true
        else
          match(a[i + skip_elems - skip_rests], elem)
        end
      end
    when :find # [*, a, b, *]
      find_match, = *args
      first, *find_match, last = *find_match
      pattern_length = find_match.length

      return false unless from.respond_to? :deconstruct
      a = from.deconstruct
      a_length = a.length
      return false if a_length < pattern_length

      # We will save the backup of returns, to be restored
      # on each iteration to try again.
      returns_backup = @returns.dup

      # Extract the capture info from first and last.
      # Both are of a form [:rest], or [:rest, :var].
      # So our new variables will be either :var, or nil.
      first, last = first[1], last[1]

      # Let's try to match each possibility...
      # [A, B, c, d], [a, B, C, d], [a, b, C, D]
      iterations = a_length - pattern_length + 1

      iterations.times.any? do |skip|
        first_part = a[0, skip]
        content = a[skip, pattern_length]
        last_part = a[skip + pattern_length..-1]

        match(first_part, first) if first
        success = content.each_with_index.all? do |e, i|
          match(e, find_match[i])
        end
        match(last_part, last) if last

        # Match failed. Let's not return anything.
        @returns = returns_backup.dup unless success

        success
      end
    when :hash # {...}
      any_size, hash_match = *args

      hash_match = hash_match.to_h

      return false unless from.respond_to? :deconstruct_keys

      if any_size && any_size != true # a => {a:, **other}
        a = from.deconstruct_keys(nil) #          ^^^^^^^
      else
        a = from.deconstruct_keys(hash_match.keys)
      end

      hash_match.all? do |k, v|
        return false unless a.key? k
        match(a[k], v)
      end || (return false)

      if any_size && any_size != true
        match(a.except(*hash_match.keys), args[0])
      elsif !any_size
        return false unless a.except(*hash_match.keys).empty?
      end

      true
    end
  end
end