PROGRAM      ←  STATEMENTS
    STATEMENTS   ←  ((COMMAND COMMENT? / COMMENT) EOX)+
    ~COMMENT     ←  ("#" / "comment" / "remark" / "rem") (!([\r\n]+).)*
    COMMAND      ←  WORD (ARGUMENTS)?
    EKEYWORD     ← "calculate" / "calc" / "expression" / "expr"
    PKEYWORD     ← "evaluate" / "eval" / "perform"
    XKEYWORD     ← "do" /  "end"
    BLOCK        ←  "do" EOX? STATEMENTS? "end" / "{" EOX? STATEMENTS? "}"
    PBLOCK       ←  PKEYWORD EOX? STATEMENTS? "end" / "[" EOX? STATEMENTS? "]"
    
    ARGUMENTS    ←  (ARGSEP? (BLOCK / PBLOCK / ARGUMENT))*
    # ARGUMENTS    ←  PREPOSITION* ARTICLE* ARGUMENT ((ARGSEP? BLOCK) /
    #                    (ARGSEP? PBLOCK) / (ARGSEP? ARGUMENT))*
    ARGSEP       ←  ',' / ((PREPOSITION / ARTICLE)+) 
    PREPOSITION  ←  < ( "else"    / "otherwise"   /
     "aboard"   / "about"       / "above"   / "across"      / "after" / "against" / 
     "alongside"/ "along"       / "amidst"  / "amidst"      / "among" / "around"  /
     "as"       / "at"          / "atop"    /  "before"     / "behind"/ "below"   /
     "beneath"  / "besides"     / "beside"  / "between"     / "beyond"/ "but"     /  
     "by"       / "circa"       / "despite" / "down"        / "during"/ "except"  /
     "for"      / "from"        / "inside"  / "into"        / "in"    / "less"    /
     "like"     / "near"        / "nothwithstanding"        / "off"   / "onto"    /
     "on"       / "opposite"    / "outside" / "out"         / "over"  / "since"   /
     "than"     / "through"     / "thru"    / "towards"     / "throughout" / "to" /
     "underneath"/ "under"      / "unlike"  / "until"       / "upon"       / "upside" /
     "up"       / "versus"      / "via"     / "within"      / "without"    / "with" ) > WHITESPACE
    ~ARTICLE     ←  <("a" / "an" / "the")> WHITESPACE
    ARGUMENT     ← EXPR
    # / NUMBER
    EXPR         ←  BINEXPR / UNEXPR
    BINEXPR      ← (ATOM (BINOP ATOM)*)
    UNEXPR       ←  (UNOP ATOM) 
    ATOM         ←  STRING / NAME / NUMBER / '(' EXPR ')' / EKEYWORD EXPR "end"
    KWUNOP       ← "not" / "negate"
    KWBINOP      ← "plus" / "minus" / "times" / "divide" /  "of" / "'s" / "'" / "and" / "or" / "equals" / "equal" / "is"
    BINOP        ←  < [-+/*] / "<-" / "->"  "&&"/ "||" / "==" / KWBINOP > 
    UNOP         ←  < [-!] / KWUNOP >   
    # / "of" / "'s"
    STRING       ← ESCSTR / RAWSTR
    # Raw string macro
    RAWSM(O,C)   ← O < (!(C).)* > C
    NAME         ← ARTICLE? WORD+ 
    # Escaped string macro.
    ESCSM(O,C)   ← O < (!(C)STRCHAR)* > C
    ESCSTR       ← ESCSM("`", "`") / ESCSM('"', '"')
    RAWSTR       ← RAWSM('<<', '>>') /  RAWSM('«', '»') / RAWSM('‹', '›') / RAWSM('“', '”')
    STRESC1      ← "\\" [nrtfv\'\\"\[\]\\]
    STRESC2      ← "\\" [0-3] [0-7] [0-7]
    STRESC3      ← "\\" [0-7] [0-7]*
    STRESC4      ← "\\x" [0-9a-fA-F] [0-9a-fA-F]?
    STRESC5      ← "\\u" [0-9a-fA-F]+
    STRNOESC     ← (!('\\\\').)
    STRCHAR      ←   STRESC1 / STRESC2 / STRESC3 / STRESC4 / STRESC5 / STRNOESC    
    NUMBER       ←  DECIMAL / INTEGER
    DECIMAL      ← < [-]?[0-9]+[.][0-9]+ >
    INTEGER      ← < [-]?[0-9]+ >
    ~EOX         ← ([ \t]*[\r\n.]+[ \t]*)+
    KEYWORD      ← PREPOSITION / ARTICLE / XKEYWORD / EKEYWORD / KWBINOP / KWUNOP
    WORD         ← !KEYWORD ANYWORD
    ANYWORD      ← < [a-zA-Z][a-zA-Z0-9]* >
    WHITESPACE   ← < [ \t]* >
    %whitespace  ←  [ \t]*
    %word        ← [a-zA-Z][-+/*a-zA-Z0-9]*
    ---
    # Expression parsing option
    %expr  = BINEXPR   # Rule to apply 'precedence climbing method' to
    %binop = L && || and or  
    %binop = L == equals equal is 
    %binop = L + - plus minus  
    %binop = L * / times divide
    %binop = L of 's <- -> ' 
    
    
    # foo bar baz quux