Cm7-lang-parser NPM

cm7-lang-parser

Cm7 is a language to represent chords and lyrics. This package is a parser for the language. See here for the language specification.

Motivation

Displaying chords on top of each line of lyrics at the correct position can be tricky. The idea is to write the chords and lyrics in a way regardless of the correct position. Then the parser transform it into AST and let the frontend to decide how to show it.

Usage

const parseCm7 = require('cm7-lang-parser');
const AST = parseCm7(cm7Src);

The AST would be in the following structure (see more here):

{
  type: string,
  text: string,
  start: number,
  end: number,
  children: AST[],
  parent: AST,
  fullText: string,
  errors: TokenError[],
  rest: string,
  fragment?: boolean,
  lookup?: boolean,
}

Language Definition

This language is defined with W3C EBNF. The ebnf definition is located here in case this README is not up to date.

cm7           ::= EOL* configs EOL+ song

configs       ::= key_config
key_config    ::= "key" WS? "=" WS? note
note          ::= [ACDFG] "#" | [ABDEG] "b" | [A-G]

song          ::= section? (EOL+ section?)*

section       ::= ("::" WS* section_label WS* "::" EOL)? line (EOL line)*
section_label ::= [^:]+

line          ::= WS* (EMPTY_LINE | chord_line) WS* (EOL WS* (EMPTY_LINE | lyrics_line) WS*)

chord_line    ::= chord (WS+ chord)*
chord         ::= relative_note quality? addition* base?
quality       ::= "mM7" | "m7b5" | "m7" | "m" | "sus2" | "sus4" |"7" | "M7" | "6" | "9" | "aug7" | "aug" | "dim7" | "dim"
addition      ::= "add" modifier? interval
base          ::= "/" relative_note
relative_note ::= ("1" | "2" | "3" | "4" | "5" | "6" | "7") ("#" | "b")?
interval      ::= "2" | "4" | "6" | "9" | "11" | "13"
modifier      ::= "#" | "b"

lyrics_line   ::= lyrics? (lyrics_beat+ lyrics?)*
lyrics        ::= [^\n\r()]+
lyrics_beat   ::= "(" lyrics? ")"

EMPTY_LINE    ::= "-"+

WS            ::= [ \t]+
EOL           ::= [\n\r]

Example Cm7 source

key=Eb

:: intro ::
1 6m
2m 5sus4 5

:: verse ::
1 6m
()在夜晚 說(早)晨
2m 5sus4 5
()閒談後 你(更)像別(人)
3m 6m
()字幕裡 說(冬)日灰暗
2m 5
回(答)你 這邊的氣(氛)

3sus4 3 6m
()就(像)你 已(記)不起了
2m 5
()連懷舊 也(格)外寂寥
3m 6m
()雜物裡 遺(物)和舊照
4 2m 2m 3m 4 5
誰(變)賣 誰(棄)掉 誰(看)(到)(破)(曉)

:: chorus ::
1 6m
()漸漸我甚(麼)都不想知道
2m 4/5
()我覺得迷(失)竟比醒覺好
3m 6m
()漸漸我離(開)都不想宣佈
2m 5sus4 5 1
()怕記憶 最(後)變話(題) 太俗(套)

3 6m 5sus4 5
() (寂)寞 寂寞出於(你)的空(白)
6m 1
()剩下我被(記)憶掌摑
2m7 3m 6m
()如留下語(錄)誰來(看)
7b 5/7
懷念(只)可鋪滿被(單)

See more examples here.