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

#append_tied(head, tail) ⇒ Object (private)

Attaches tail at the deep end of head’s tied chain, rebuilding each link (RhythmicValue exposes no setter) so a chain like “half tied to eighth” gains a further “tied to quarter”.



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# File 'lib/head_music/notation/abc/parser.rb', line 361

def append_tied(head, tail)
  inner = head.tied_value ? append_tied(head.tied_value, tail) : tail
  HeadMusic::Rudiment::RhythmicValue.new(head.unit, dots: head.dots, tied_value: inner)
end

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



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# File 'lib/head_music/notation/abc/parser.rb', line 371

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 399

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 69

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

#chord_snippet(token) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 207

def chord_snippet(token)
  inner = token.notes.map do |note|
    "#{note.accidental}#{note.letter}#{note.octave_marks}#{note.length}"
  end.join
  "[#{inner}]"
end

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



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# File 'lib/head_music/notation/abc/parser.rb', line 392

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 148

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

#defer_placement(state, pitches, length, inner_scale = Rational(1)) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 214

def defer_placement(state, pitches, length, inner_scale = Rational(1))
  scale = (state.awaiting_scale || Rational(1)) * inner_scale
  state.awaiting_scale = nil
  return tie_onto_pending(state, pitches, length, scale) if state.tie_open

  flush_pending_note(state)
  state.pending_note = PendingNote.new(pitches: pitches, length: length, scale: scale)
end

#ensure_input_present ⇒ Object (private)

Raises:



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# File 'lib/head_music/notation/abc/parser.rb', line 79

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 334

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

#ensure_tie_pitches_match(state, pending, pitches) ⇒ Object (private)

Raises:



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# File 'lib/head_music/notation/abc/parser.rb', line 251

def ensure_tie_pitches_match(state, pending, pitches)
  return if pending.pitches.sort == pitches.sort

  raise ParseError.new(
    "A tie must connect two notes of the same pitch",
    line_number: state.tie_line, snippet: "-"
  )
end

#ensure_unique_chord_pitches(pitches, token) ⇒ Object (private)

Raises:



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# File 'lib/head_music/notation/abc/parser.rb', line 183

def ensure_unique_chord_pitches(pitches, token)
  return if pitches.uniq.length == pitches.length

  raise ParseError.new(
    "Chord pitches must be unique",
    line_number: token.line, snippet: chord_snippet(token)
  )
end

#finish ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 325

def finish
  @voice_states.each_value do |state|
    ensure_not_awaiting_note(nil, state: state)
    reject_open_tie(state, nil, "A tie must be followed by a note")
    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 343

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

  state.pending_note = nil
  state.voice.place(state.voice.next_position, pending_rhythmic_value(pending), pending.pitches)
end

#handle(token) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 152

def handle(token)
  case token.type
  when :note then handle_note(token)
  when :chord then handle_chord(token)
  when :rest then handle_rest(token)
  when :tie then handle_tie(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 292

def handle_bar_line(token)
  ensure_not_awaiting_note(token)
  state = current_state
  reject_open_tie(state, token.line, "Ties across barlines are not yet supported")
  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 277

def handle_broken_rhythm(token)
  state = current_state
  reject_open_tie(state, token.line, "A tie must be followed by a note")
  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_chord(token) ⇒ Object (private)

Chord pitches resolve in bracket order, so an explicit accidental inside a chord persists for the rest of the bar like any other.



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

def handle_chord(token)
  state = current_state
  pitches = token.notes.map do |note|
    state.pitch_builder.pitch(note.letter, note.octave_marks, note.accidental)
  end
  ensure_unique_chord_pitches(pitches, token)
  inner_length = uniform_chord_length(token)
  defer_placement(state, pitches, token.length, inner_length)
end

#handle_note(token) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 165

def handle_note(token)
  state = current_state
  pitch = state.pitch_builder.pitch(token.letter, token.octave_marks, token.accidental)
  defer_placement(state, [pitch], token.length)
end

#handle_rest(token) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 260

def handle_rest(token)
  ensure_not_awaiting_note(token)
  state = current_state
  reject_open_tie(state, token.line, "A tie must be followed by a note")
  flush_pending_note(state)
  place(state, token.length, nil)
end

#handle_tie(token) ⇒ Object (private)

A tie (-) after a note or chord fuses it to the next note of the same pitch. The left note stays pending; the tie is only closed once its right note arrives.



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# File 'lib/head_music/notation/abc/parser.rb', line 226

def handle_tie(token)
  state = current_state
  if state.awaiting_scale || state.pending_note.nil?
    raise ParseError.new(
      "A tie must follow a note", line_number: token.line, snippet: "-"
    )
  end
  state.tie_open = true
  state.tie_line = token.line
end

#handle_voice_change(token) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 315

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)
    reject_open_tie(@current_state, token.line, "A tie must be followed by a note")
    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 303

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
  reject_open_tie(state, token.line, "A tie must be followed by a note")
  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 116

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

#pending_rhythmic_value(pending) ⇒ Object (private)

A pending note’s own value, with any tied prefix appended ahead of it so the whole tie chain renders as one sounding note.



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# File 'lib/head_music/notation/abc/parser.rb', line 353

def pending_rhythmic_value(pending)
  own = duration_resolver.rhythmic_value(pending.length, scale: pending.scale)
  pending.tied_prefix ? append_tied(pending.tied_prefix, own) : own
end

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



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# File 'lib/head_music/notation/abc/parser.rb', line 366

def place(state, length, pitches, scale: Rational(1))
  rhythmic_value = duration_resolver.rhythmic_value(length, scale: scale)
  state.voice.place(state.voice.next_position, rhythmic_value, pitches)
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 87

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_open_tie(state, line, message) ⇒ Object (private)

A tie left open by a non-note terminator can never close, so each terminator rejects it. A bar line gets its own message: an author tie across a barline is a real, but not-yet-supported, request.

Raises:



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# File 'lib/head_music/notation/abc/parser.rb', line 271

def reject_open_tie(state, line, message)
  return unless state&.tie_open

  raise ParseError.new(message, line_number: line || state.tie_line, snippet: "-")
end

#reject_unsupported_tokens(tokens) ⇒ Object (private)

Raises:



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# File 'lib/head_music/notation/abc/parser.rb', line 106

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 131

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 383

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

#tie_onto_pending(state, pitches, length, scale) ⇒ Object (private)

Closes an open tie: the pending note becomes the new note’s tied prefix, so the pair (and any longer chain) resolves to a single placement whose rhythmic value carries the author’s chosen split.



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# File 'lib/head_music/notation/abc/parser.rb', line 240

def tie_onto_pending(state, pitches, length, scale)
  pending = state.pending_note
  ensure_tie_pitches_match(state, pending, pitches)
  prefix = pending_rhythmic_value(pending)
  state.tie_open = false
  state.tie_line = nil
  state.pending_note = PendingNote.new(
    pitches: pitches, length: length, scale: scale, tied_prefix: prefix
  )
end

#uniform_chord_length(token) ⇒ Object (private)

ABC 2.1 sec. 4.17 allows per-note lengths only when they agree; the shared inner length then multiplies with any outer length. Unequal lengths (whose ABC meaning is “the duration of the first note”) would need silent reinterpretation to fit one rhythmic value, so we reject.

Raises:



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# File 'lib/head_music/notation/abc/parser.rb', line 196

def uniform_chord_length(token)
  fractions = token.notes.map { |note| duration_resolver.length_fraction(note.length) }
  return fractions.first if fractions.uniq.length == 1

  raise ParseError.new(
    'Chord notes must share one length; write it after the bracket ("[CEG]2") ' \
    'or repeat it on every note ("[C2E2G2]")',
    line_number: token.line, snippet: chord_snippet(token)
  )
end

#voice_state(role) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 140

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