template.pegjs

{ function j(string) { return string.join('') } }
  
template =
  (
    interpolation /
    tag /
    $(!interpolation !tag .)
  )+

ws = (" " / "\n")*
value = [^ ]

// {{ this }}
open_interpolation = "{{"
close_interpolation = "}}"

not_close_interpolation =
  ws !close_interpolation m:value ws { return m }

interpolation =
  open_interpolation m:not_close_interpolation+ close_interpolation { return j(m) }

// {% this %}
open_tag = "{%"
close_tag = "%}"

not_close_tag =
  ws !close_tag m:value ws { return m }

tag_start = !tag_end open_tag m:not_close_tag+ close_tag { return j(m) }

tag_end = open_tag ws "end" not_close_tag+ close_tag

tag = tag_start template tag_end