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 295

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 323

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

#chord_snippet(token) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 200

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 316

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

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



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

def defer_placement(state, pitches, length, inner_scale = Rational(1))
  scale = (state.awaiting_scale || Rational(1)) * inner_scale
  state.awaiting_scale = nil
  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 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 273

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_unique_chord_pitches(pitches, token) ⇒ Object (private)

Raises:



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# File 'lib/head_music/notation/abc/parser.rb', line 176

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 265

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 282

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

  state.pending_note = nil
  place(state, pending.length, pending.pitches, 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 :chord then handle_chord(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 235

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 221

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_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 166

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 158

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 214

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 256

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 245

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, pitches, scale: Rational(1)) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 290

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 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 307

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

#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 189

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 134

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