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.

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 259

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 288

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

#build_composition ⇒ Object (private)

Per-voice interpretation state and note-assembly live in VoiceState.



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# File 'lib/head_music/notation/abc/parser.rb', line 39

def build_composition
  Preflight.ensure_input_present(@abc_string)
  @header = Header.new(@abc_string, start_line: @start_line)
  Preflight.reject_content_after_tune(header)
  tokens = BodyLexer.new(header.body, start_line: header.body_start_line).tokens
  Preflight.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 142

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 281

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 82

def current_state
  @current_state ||= voice_state(nil)
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 250

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 118

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 241

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")
    state.flush_pending_note
    tag_completed_bar(state)
  end
end

#handle(token) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 86

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)
  when :beam_break then handle_beam_break(token)
  end
end

#handle_bar_line(token) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 203

def handle_bar_line(token)
  ensure_not_awaiting_note(token)
  state = current_state
  style = token.style
  reject_open_tie(state, token.line, "Ties across barlines are not yet supported")
  state.flush_pending_note
  state.reset_beam_adjacency
  tag_completed_bar(state)
  apply_repeat_flags(state, style)
  clear_passes_if_over(state, style)
  state.pitch_builder.start_new_bar
end

#handle_beam_break(_token) ⇒ Object (private)

The lexer only emits :beam_break after a music token, so a voice state already exists; the flag is consumed by the next deferred note.



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# File 'lib/head_music/notation/abc/parser.rb', line 151

def handle_beam_break(_token)
  current_state.mark_beam_break
end

#handle_broken_rhythm(token) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 185

def handle_broken_rhythm(token)
  state = current_state
  line = token.line
  direction = token.direction
  reject_open_tie(state, line, "A tie must be followed by a note")
  pending = state.pending_note
  if state.awaiting_scale || pending.nil?
    raise ParseError.new(
      "Broken rhythm must appear between two notes",
      line_number: line, snippet: direction.to_s
    )
  end
  left_scale, right_scale = BROKEN_RHYTHM_SCALES.fetch(direction)
  state.pending_note = pending.with(scale: pending.scale * left_scale)
  state.awaiting_scale = right_scale
  state.broken_line = 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 108

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)
  state.defer_placement(pitches, token.length, inner_length)
end

#handle_note(token) ⇒ Object (private) 



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

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

#handle_rest(token) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 167

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")
  state.flush_pending_note
  state.reset_beam_adjacency
  state.place(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 158

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

#handle_voice_change(token) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 230

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")
    @current_state.flush_pending_note
    @current_state.reset_beam_adjacency
  end
  @current_state = voice_state(token.voice_id)
end

#handle_volta(token) ⇒ Object (private)

Raises:



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# File 'lib/head_music/notation/abc/parser.rb', line 216

def handle_volta(token)
  ensure_not_awaiting_note(token)
  passes = token.passes
  line = token.line
  raise ParseError.new("Volta has no passes", line_number: line) if passes.empty?

  state = current_state
  reject_open_tie(state, line, "A tie must be followed by a note")
  state.flush_pending_note
  state.reset_beam_adjacency
  state.active_passes = 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 49

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

#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 179

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

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

#setup_voices(tokens) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/parser.rb', line 64

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 271

def tag_completed_bar(state)
  passes = state.active_passes
  return unless passes

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

  bar(completed).plays_on_passes = 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 131

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 73

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