Class: PatternMatching

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# File 'opal/opal/corelib/pattern_matching.rb', line 12
def initialize(from, pattern)
 @from, @pattern = from, pattern
 @returns = []
end

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# File 'opal/opal/corelib/pattern_matching.rb', line 17
def returns
 @returns
end

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# File 'opal/opal/corelib/pattern_matching.rb', line 6
def self.call(from, pattern)
 pm = new(from, pattern)
 pm.match || (return nil)
 pm.returns
end

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# File 'opal/opal/corelib/pattern_matching.rb', line 19
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