grammar Canopy.MetaGrammar

# ==============================================================================

grammar               <-  _* grammar_name (_* rule)+ _* %grammar

grammar_name          <-  `grammar` ":"? _+ id:object_identifier

rule                  <-  identifier assignment parsing_expression %rule

assignment            <-  _+ "<-" _+

# ==============================================================================

_                     <-  [ \t\n\r] / comment

comment               <-  "#" [^\n]*

object_identifier     <-  identifier ("." identifier)*

identifier            <-  [a-zA-Z_] [a-zA-Z0-9_]*

integer               <-  [1-9] [0-9]*

# ==============================================================================

parsing_expression    <-  choice
                       /  choice_part

choice_part           <-  action_expression
                       /  typed_expression
                       /  sequence
                       /  sequence_element

sequence_element      <-  predicated_atom
                       /  repeated_atom
                       /  maybe_atom
                       /  atom

atom                  <-  reference
                       /  terminal
                       /  paren_expression

terminal              <-  literal_string
                       /  ci_string
                       /  char_class
                       /  any_char

# ==============================================================================

action_expression     <-  actionable _+ action_tag %action

actionable            <-  sequence
                       /  repeated_atom
                       /  maybe_atom
                       /  terminal
                       /  "(" _* actionable _* ")" %paren_expr

action_tag            <-  "%" id:identifier

# ==============================================================================

typed_expression      <-  typable _+ type_tag %extension

typable               <-  sequence
                       /  sequence_element

type_tag              <-  "<" id:object_identifier ">"

# ==============================================================================

choice                <-  choice_part (_* "/" _* expr:choice_part)+ %choice

# ==============================================================================

sequence              <-  sequence_part (_+ expr:sequence_part)+ %sequence

sequence_part         <-  mute? label? sequence_element %sequence_part

mute                  <-  "@"

label                 <-  id:identifier ":"

# ==============================================================================

repeated_atom         <-  atom _* quantifier %repeat

quantifier            <-  "*" / "+" / "{" _* numeric_quantifier _* "}"

numeric_quantifier    <-  min:integer max:(_* "," _* n:integer?)?

# ==============================================================================

paren_expression      <-  "(" _* parsing_expression _* ")" %paren_expr

predicated_atom       <-  ("&" / "!") _* atom %predicate

maybe_atom            <-  atom _* "?" %maybe

reference             <-  identifier !assignment %reference

literal_string        <-  '"' ("\\" . / [^"])* '"' %string
                       /  "'" ("\\" . / [^'])* "'" %string

ci_string             <-  "`" ("\\" . / [^`])* "`" %ci_string

char_class            <-  "[" "^"? ("\\" . / [^\]])+ "]" %char_class

any_char              <-  "." %any_char