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%{
(*
Notes about error messages and error locations in ocamlyacc:
1) There is a predefined "error" symbol which can be used as a catch-all,
in order to get the location of the token that shouldn't be there.
2) Additional rules that match common errors are added, so that when
they are matched, a nice, handcrafted error message is produced.
3) Token locations are retrieved using functions from the Parsing
module, which relies on a global state. If you want your error locations
to be reliable, don't run two ocamlyacc parsers simultaneously.
In the end, the error messages are nicer than the ones that a camlp4
parser (extensible grammar) would produce because we write them
manually. However camlp4's messages are all automatic,
i.e. they tell you which tokens were expected at a given location.
For the file/line/char locations to be correct,
the lexbuf must be adjusted by the lexer when the file name
changes or a new line is encountered. This is not performed automatically
by ocamllex, see file json_lexer.mll.
*)
open Printf
open Json_type
let rhs_loc n = (Parsing.rhs_start_pos n, Parsing.rhs_end_pos n)
let unclosed opening_name opening_num closing_name closing_num =
let msg =
sprintf "%s:\nSyntax error: '%s' expected.\n\
%s:\nThis '%s' might be unmatched."
(string_of_loc (rhs_loc closing_num)) closing_name
(string_of_loc (rhs_loc opening_num)) opening_name in
json_error msg
let syntax_error s num =
let msg = sprintf "%s:\n%s" (string_of_loc (rhs_loc num)) s in
json_error msg
%}
%token <string> STRING
%token <int> INT
%token <float> FLOAT
%token <bool> BOOL
%token OBJSTART OBJEND ARSTART AREND NULL COMMA COLON
%token EOF
%start main
%type <Json_type.t> main
%%
main:
| value EOF { $1 }
| value error { syntax_error "Junk after end of data" 2 }
| EOF { syntax_error "Empty data" 1 }
| error { syntax_error "Syntax error" 1 }
;
value:
| OBJSTART pair_list OBJEND { Object $2 }
| OBJSTART OBJEND { Object [] }
| OBJSTART pair_list EOF { unclosed "{" 1 "}" 3 }
| OBJSTART pair_list error { unclosed "{" 1 "}" 3 }
| OBJSTART error { syntax_error
"Expecting a comma-separated sequence \
of string:value pairs" 2 }
| ARSTART value_list AREND { Array $2 }
| ARSTART AREND { Array [] }
| ARSTART value_list EOF { unclosed "[" 1 "]" 3 }
| ARSTART value_list error { unclosed "[" 1 "]" 3 }
| ARSTART error { syntax_error
"Expecting a comma-separated sequence \
of values" 2 }
| STRING { String $1 }
| BOOL { Bool $1 }
| NULL { Null }
| INT { Int $1 }
| FLOAT { Float $1 }
;
pair_list:
| STRING COLON value COMMA pair_list { ($1, $3) :: $5 }
| STRING COLON value COMMA OBJEND
{ syntax_error
"End-of-object commas are illegal" 4 }
| STRING COLON value STRING { syntax_error "Missing ','" 4 }
| STRING COLON value { [ ($1, $3) ] }
;
value_list:
| value COMMA value_list { $1 :: $3 }
| value COMMA AREND { syntax_error
"End-of-array commas are illegal" 2 }
| value value { syntax_error "Missing ',' before this value" 2 }
| value { [ $1 ] }
;
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