Class: HeadMusic::Notation::ABC::Parser

Inherits:
Object
  • Object
show all
Defined in:
lib/head_music/notation/abc/parser.rb

Overview

Interprets an ABC tune string as a HeadMusic::Content::Composition.

Everything that can be validated up front (blank input, header problems, lexing errors, unsupported features) raises before the composition is constructed, so callers never receive a reference to a partially built composition.

Defined Under Namespace

Classes: PendingNote, VoiceState

Constant Summary collapse

BROKEN_RHYTHM_SCALES =

Broken-rhythm scales: the mark’s side gets the dot (x 3/2) and the other side is halved.

{
  :> => [Rational(3, 2), Rational(1, 2)],
  :< => [Rational(1, 2), Rational(3, 2)]
}.freeze
REPEAT_ENDING_STYLES =

Bar styles that end a repeated section, terminating any volta.

[":|", "::"].freeze
REPEAT_STARTING_STYLES = 
["|:", "::"].freeze
SECTION_ENDING_STYLES = 
["||", "|]", "[|"].freeze

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(abc_string, start_line: 1) ⇒ Parser

start_line offsets reported line numbers, so a tune parsed out of a larger book raises errors with book-relative line numbers.



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# File 'lib/head_music/notation/abc/parser.rb', line 24

def initialize(abc_string, start_line: 1)
  @abc_string = abc_string
  @start_line = start_line
end

Instance Attribute Details

#duration_resolver ⇒ Object (readonly, private)

Returns the value of attribute duration_resolver.



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# File 'lib/head_music/notation/abc/parser.rb', line 35

def duration_resolver
  @duration_resolver
end

#header ⇒ Object (readonly, private)

Returns the value of attribute header.



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# File 'lib/head_music/notation/abc/parser.rb', line 35

def header
  @header
end

Instance Method Details

#apply_repeat_flags(state, style) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 247

def apply_repeat_flags(state, style)
  if REPEAT_ENDING_STYLES.include?(style)
    completed = state.completed_bar_number
    bar(completed).ends_repeat_after_num_plays = 2 if completed
  end
  return unless REPEAT_STARTING_STYLES.include?(style)

  bar(state.entered_bar_number).starts_repeat = true
end

#bar(bar_number) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 275

def bar(bar_number)
  @building.bars(bar_number).last
end

#build_composition ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 63

def build_composition
  ensure_input_present
  @header = Header.new(@abc_string, start_line: @start_line)
  reject_content_after_tune
  tokens = BodyLexer.new(header.body, start_line: header.body_start_line).tokens
  reject_unsupported_tokens(tokens)
  @duration_resolver = DurationResolver.new(header.unit_note_length)
  interpret(tokens)
end

#clear_passes_if_over(state, style) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 268

def clear_passes_if_over(state, style)
  return unless REPEAT_ENDING_STYLES.include?(style) || SECTION_ENDING_STYLES.include?(style)

  state.active_passes = nil
  state.volta_start_bar = nil
end

#composition ⇒ Object 



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# File 'lib/head_music/notation/abc/parser.rb', line 29

def composition
  @composition ||= build_composition
end

#current_state ⇒ Object (private)

Body music before any V: line falls into a default unnamed voice.



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# File 'lib/head_music/notation/abc/parser.rb', line 142

def current_state
  @current_state ||= voice_state(nil)
end

#ensure_input_present ⇒ Object (private)

Raises:



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# File 'lib/head_music/notation/abc/parser.rb', line 73

def ensure_input_present
  return unless @abc_string.to_s.strip.empty?

  raise ParseError, "ABC input is blank"
end

#ensure_not_awaiting_note(token, state: current_state) ⇒ Object (private)

Raises:



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# File 'lib/head_music/notation/abc/parser.rb', line 225

def ensure_not_awaiting_note(token, state: current_state)
  return unless state.awaiting_scale

  raise ParseError.new(
    "Broken rhythm must be followed by a note",
    line_number: token&.line || state.broken_line
  )
end

#finish ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 217

def finish
  @voice_states.each_value do |state|
    ensure_not_awaiting_note(nil, state: state)
    flush_pending_note(state)
    tag_completed_bar(state)
  end
end

#flush_pending_note(state) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 234

def flush_pending_note(state)
  pending = state.pending_note
  return unless pending

  state.pending_note = nil
  place(state, pending.length, pending.pitch, scale: pending.scale)
end

#handle(token) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 146

def handle(token)
  case token.type
  when :note then handle_note(token)
  when :rest then handle_rest(token)
  when :broken_rhythm then handle_broken_rhythm(token)
  when :bar_line then handle_bar_line(token)
  when :volta then handle_volta(token)
  when :voice_change then handle_voice_change(token)
  end
end

#handle_bar_line(token) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 187

def handle_bar_line(token)
  ensure_not_awaiting_note(token)
  state = current_state
  flush_pending_note(state)
  tag_completed_bar(state)
  apply_repeat_flags(state, token.style)
  clear_passes_if_over(state, token.style)
  state.pitch_builder.start_new_bar
end

#handle_broken_rhythm(token) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 173

def handle_broken_rhythm(token)
  state = current_state
  if state.awaiting_scale || state.pending_note.nil?
    raise ParseError.new(
      "Broken rhythm must appear between two notes",
      line_number: token.line, snippet: token.direction.to_s
    )
  end
  left_scale, right_scale = BROKEN_RHYTHM_SCALES.fetch(token.direction)
  state.pending_note = state.pending_note.with(scale: state.pending_note.scale * left_scale)
  state.awaiting_scale = right_scale
  state.broken_line = token.line
end

#handle_note(token) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 157

def handle_note(token)
  state = current_state
  pitch = state.pitch_builder.pitch(token.letter, token.octave_marks, token.accidental)
  scale = state.awaiting_scale || Rational(1)
  state.awaiting_scale = nil
  flush_pending_note(state)
  state.pending_note = PendingNote.new(pitch: pitch, length: token.length, scale: scale)
end

#handle_rest(token) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 166

def handle_rest(token)
  ensure_not_awaiting_note(token)
  state = current_state
  flush_pending_note(state)
  place(state, token.length, nil)
end

#handle_voice_change(token) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 208

def handle_voice_change(token)
  # Guarded so a leading V: line doesn't force a default voice into existence.
  if @current_state
    ensure_not_awaiting_note(token, state: @current_state)
    flush_pending_note(@current_state)
  end
  @current_state = voice_state(token.voice_id)
end

#handle_volta(token) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 197

def handle_volta(token)
  ensure_not_awaiting_note(token)
  if token.passes.empty?
    raise ParseError.new("Volta has no passes", line_number: token.line)
  end
  state = current_state
  flush_pending_note(state)
  state.active_passes = token.passes
  state.volta_start_bar = state.entered_bar_number
end

#interpret(tokens) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 110

def interpret(tokens)
  @building = HeadMusic::Content::Composition.new(
    name: header.title,
    key_signature: header.key_signature,
    meter: header.meter,
    composer: header.composer,
    origin: header.origin,
    comments: header.annotations
  )
  setup_voices(tokens)
  tokens.each { |token| handle(token) }
  finish
  @building
end

#place(state, length, pitch, scale: Rational(1)) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 242

def place(state, length, pitch, scale: Rational(1))
  rhythmic_value = duration_resolver.rhythmic_value(length, scale: scale)
  state.voice.place(state.voice.next_position, rhythmic_value, pitch)
end

#reject_content_after_tune ⇒ Object (private)

The lexer treats a blank line as the end of the tune, so anything after it would be silently dropped — most likely another tune.

Raises:



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# File 'lib/head_music/notation/abc/parser.rb', line 81

def reject_content_after_tune
  lines = header.body.lines
  blank_index = lines.find_index { |line| line.strip.empty? }
  return unless blank_index

  extra_lines = lines[(blank_index + 1)..]
  extra_index = extra_lines.find_index do |line|
    stripped = line.strip
    !stripped.empty? && !stripped.start_with?("%")
  end
  return unless extra_index

  raise ParseError.new(
    "Content after the tune body; parse a book of tunes with ABC.parse_book",
    line_number: header.body_start_line + blank_index + 1 + extra_index,
    snippet: extra_lines[extra_index].strip[0, BodyLexer::SNIPPET_LENGTH]
  )
end

#reject_unsupported_tokens(tokens) ⇒ Object (private)

Raises:



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# File 'lib/head_music/notation/abc/parser.rb', line 100

def reject_unsupported_tokens(tokens)
  token = tokens.find { |candidate| candidate.type == :unsupported }
  return unless token

  raise UnsupportedFeatureError.new(
    "Unsupported ABC feature #{token.lexeme.inspect}",
    line_number: token.line, snippet: token.lexeme
  )
end

#setup_voices(tokens) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 125

def setup_voices(tokens)
  @voice_states = {}
  header.voice_ids.each { |voice_id| voice_state(voice_id) }
  if @voice_states.empty? && tokens.none? { |token| token.type == :voice_change }
    voice_state(nil)
  end
  @current_state = @voice_states.values.first
end

#tag_completed_bar(state) ⇒ Object (private)

A volta covers every bar from its opening bracket through the bar line that ends it, so each completed bar in that span gets tagged.



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# File 'lib/head_music/notation/abc/parser.rb', line 259

def tag_completed_bar(state)
  return unless state.active_passes

  completed = state.completed_bar_number
  return unless completed && completed >= state.volta_start_bar

  bar(completed).plays_on_passes = state.active_passes
end

#voice_state(role) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 134

def voice_state(role)
  @voice_states[role] ||= VoiceState.new(
    @building.add_voice(role: role),
    PitchBuilder.new(header.key_signature)
  )
end