peg.js for sherwinkeys

start =
  Seq

Seq = 
  first: Expr "_" rest:Seq {return {tag: "Seq", first: first, rest: rest} }
  / Expr

Expr = 
    WrappedEvent
  / Event
  / "(" e:Event ")" {return e;}
  / "(" e:Seq ")" {return e;}

Event = 
    BasicEvent
  / MultiEvent

BasicEvent = 
  letters:[a-z]+ { return letters.join(""); }

MultiEvent = 
  "{" (BasicEvent ","?)+ "}"

WrappedEvent =
    wrap:Event "+" inner:Expr { return {outer: wrap, inner: inner} }
  / wrap:Event "+" inner:WrappedEvent { return {outer: wrap, inner: inner} }

v2

{

  pairsToObject = function(pairs) {
    var ret = {};
    pairs.forEach( function(pair) {
      ret[pair[0]] = pair[1];
    });
    return ret;
  }

}



start =
  Seq
 

Seq = 
  first:Expr
  SequentiationOperator
  rest:Seq
  {return {tag: "Seq", first: first, rest: rest} }

  / Expr


SequentiationOperator = "_"+
 

Expr = 
    e:WrappedEvent
    opts:OptionList?
    { e.opts = opts; return e;}

  / e:Event
    opts:OptionList?
    { e.opts = opts; return e;}

  / "("
     e:Event
     opts:OptionList?
     ")"
     {e.opts = opts; return e;}

  / "("
     e:Seq
     opts:OptionList?
     ")"
    { e.opts = opts; return e;}
 

Event = 
    BasicEvent
  / MultiEvent
 

BasicEvent = 
  letters:[a-z]+ { return {event: letters.join("")}; }
 

MultiEvent = 
   MultiEventStart
   events:(e:BasicEvent MultiEventSeparator? {return e})+
   MultiEventEnd 
   { return {tag: "multi", events: events} }

MultiEventStart = "{"
MultiEventSeparator = ","
MultiEventEnd = "}"
 

WrappedEvent =
    wrap:Event "+" inner:Expr
    { return {outer: wrap, inner: inner} }

  / wrap:Event "+" inner:WrappedEvent
    { return {outer: wrap, inner: inner} }


Option = 
   key:[a-z]+ "=" val:[a-z]+ { return [key.join(""), val.join("")] }

OptionList = 
   WhiteSpace "::" WhiteSpace first:Option rest:(OptionSeparator o:Option {return o})* { return pairsToObject([first].concat(rest)) }

OptionSeparator = 
  WhiteSpace ";" WhiteSpace

WhiteSpace = 
  [ \t]*

v3

{

  pairsToObject = function(pairs) {
    var ret = {};
    pairs.forEach( function(pair) {
      ret[pair[0]] = pair[1];
    });
    return ret;
  }

}



start =
  Seq
 

Seq = 
  first:Expr
  SequentiationOperator
  rest:Seq
  {return {tag: "Seq", first: first, rest: rest} }

  / Expr


SequentiationOperator = [_|.]+
 

Expr = 
    e:WrappedEvent
    opts:OptionList?
    { e.opts = opts; return e;}

  / e:Event
    opts:OptionList?
    { e.opts = opts; return e;}

  / "("
     e:Event
     opts:OptionList?
     ")"
     {e.opts = opts; return e;}

  / "("
     e:Seq
     opts:OptionList?
     ")"
    { e.opts = opts; return e;}
 

Event = 
    BasicEvent
  / MultiEvent
 

BasicEvent = 
  letters:[a-z0-9]+ { return {event: letters.join("")}; }
 

MultiEvent = 
   MultiEventStart
   events:(e:BasicEvent MultiEventSeparator? {return e})+
   MultiEventEnd 
   { return {tag: "multi", events: events} }

MultiEventStart = "{"
MultiEventSeparator = ","
MultiEventEnd = "}"
 

WrappedEvent =
    wrap:Event "+" inner:Expr
    { return {outer: wrap, inner: inner} }
  
  / wrap:Event "+" inner:WrappedEvent
    { return {outer: wrap, inner: inner} }


Option = 
   key:[a-z]+ "=" val:[a-z]+ { return [key.join(""), val.join("")] }

OptionList = 
   WhiteSpace "::" WhiteSpace first:Option rest:(OptionSeparator o:Option {return o})* { return pairsToObject([first].concat(rest)) }

OptionSeparator = 
  WhiteSpace ";" WhiteSpace

WhiteSpace = 
  [ \t]*