I have a parser and lexer written in ocamlyacc and ocamllex. If the file to parse ends prematurely, as in I forget a semicolon at the end of a line, the application doesn't raise a syntax error. I realize it's because I'm raising and catching EOF and that is making the lexer ignore the unfinished rule, but how should I be doing this to raise a syntax error?
Here is my current parser (simplified),
%{
let parse_error s = Printf.ksprinf failwith "ERROR: %s" s
%}
%token COLON
%token SEPARATOR
%token SEMICOLON
%token <string> FLOAT
%token <string> INT
%token <string> LABEL
%type <Conf.config> command
%start command
%%
command:
| label SEPARATOR data SEMICOLON { Conf.Pair ($1,$3) }
| label SEPARATOR data_list { Conf.List ($1,$3) }
| label SEMICOLON { Conf.Single ($1) }
label :
| LABEL { Conf.Label $1 }
data :
| label { $1 }
| INT { Conf.Integer $1 }
| FLOAT { Conf.Float $1 }
data_list :
| star_data COMMA star_data data_list_ending
{ $1 :: $3 :: $4 }
data_list_ending:
| COMMA star_data data_list_ending { $2 :: $3 }
| SEMICOLON { [] }
and lexxer (simplified),
{
open ConfParser
exception Eof
}
rule token = parse
| ['\t' ' ' '\n' '\010' '\013' '\012']
{ token lexbuf }
| ['0'-'9']+ ['.'] ['0'-'9']* ('e' ['-' '+']? ['0'-'9']+)? as n
{ FLOAT n }
| ['0'-'9']+ as n { INT n }
| '#' { comment lexbuf }
| ';' { SEMICOLON }
| ['=' ':'] { SEPARATOR }
| ',' { COMMA }
| ['_' 'a'-'z' 'A'-'Z']([' ']?['a'-'z' 'A'-'Z' '0'-'9' '_' '-' '.'])* as w
{ LABEL w }
| eof { raise Eof }
and comment = parse
| ['#' '\n'] { token lexbuf }
| _ { comment lexbuf }
example input file,
one = two, three, one-hundred;
single label;
list : command, missing, a, semicolon
One solution, is to add a recursive call in the command rule to itself at the end, and adding an empty rule, all of which build a list to return to the main program. I think I maybe interpreting Eof as a expectation, and ending condition, rather then an error in the lexer, is this correct?