1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
|
# ebnf-parser
A parser for BNF and EBNF grammars used by jison.
## install
npm install ebnf-parser
## build
To build the parser yourself, clone the git repo then run:
make
This will generate `parser.js`, which is required by `ebnf-parser.js`.
## usage
The parser translates a string grammar or JSON grammar into a JSON grammar that jison can use (ENBF is transformed into BNF).
var ebnfParser = require('ebnf-parser');
// parse a bnf or ebnf string grammar
ebnfParser.parse("%start ... %");
// transform an ebnf JSON gramamr
ebnfParser.transform({"ebnf": ...});
## example grammar
The parser can parse its own BNF grammar, shown below:
%start spec
/* grammar for parsing jison grammar files */
%{
var transform = require('./ebnf-transform').transform;
var ebnf = false;
%}
%%
spec
: declaration_list '%%' grammar optional_end_block EOF
{$$ = $1; return extend($$, $3);}
| declaration_list '%%' grammar '%%' CODE EOF
{$$ = $1; yy.addDeclaration($$,{include:$5}); return extend($$, $3);}
;
optional_end_block
:
| '%%'
;
declaration_list
: declaration_list declaration
{$$ = $1; yy.addDeclaration($$, $2);}
|
{$$ = {};}
;
declaration
: START id
{$$ = {start: $2};}
| LEX_BLOCK
{$$ = {lex: $1};}
| operator
{$$ = {operator: $1};}
| ACTION
{$$ = {include: $1};}
;
operator
: associativity token_list
{$$ = [$1]; $$.push.apply($$, $2);}
;
associativity
: LEFT
{$$ = 'left';}
| RIGHT
{$$ = 'right';}
| NONASSOC
{$$ = 'nonassoc';}
;
token_list
: token_list symbol
{$$ = $1; $$.push($2);}
| symbol
{$$ = [$1];}
;
grammar
: production_list
{$$ = $1;}
;
production_list
: production_list production
{$$ = $1;
if($2[0] in $$) $$[$2[0]] = $$[$2[0]].concat($2[1]);
else $$[$2[0]] = $2[1];}
| production
{$$ = {}; $$[$1[0]] = $1[1];}
;
production
: id ':' handle_list ';'
{$$ = [$1, $3];}
;
handle_list
: handle_list '|' handle_action
{$$ = $1; $$.push($3);}
| handle_action
{$$ = [$1];}
;
handle_action
: handle prec action
{$$ = [($1.length ? $1.join(' ') : '')];
if($3) $$.push($3);
if($2) $$.push($2);
if ($$.length === 1) $$ = $$[0];
}
;
handle
: handle expression_suffix
{$$ = $1; $$.push($2)}
|
{$$ = [];}
;
handle_sublist
: handle_sublist '|' handle
{$$ = $1; $$.push($3.join(' '));}
| handle
{$$ = [$1.join(' ')];}
;
expression_suffix
: expression suffix
{$$ = $expression + $suffix; }
;
expression
: ID
{$$ = $1; }
| STRING
{$$ = ebnf ? "'"+$1+"'" : $1; }
| '(' handle_sublist ')'
{$$ = '(' + $handle_sublist.join(' | ') + ')'; }
;
suffix
: {$$ = ''}
| '*'
| '?'
| '+'
;
prec
: PREC symbol
{$$ = {prec: $2};}
|
{$$ = null;}
;
symbol
: id
{$$ = $1;}
| STRING
{$$ = yytext;}
;
id
: ID
{$$ = yytext;}
;
action
: '{' action_body '}'
{$$ = $2;}
| ACTION
{$$ = $1;}
| ARROW_ACTION
{$$ = '$$ ='+$1+';';}
|
{$$ = '';}
;
action_body
:
{$$ = '';}
| ACTION_BODY
{$$ = yytext;}
| action_body '{' action_body '}' ACTION_BODY
{$$ = $1+$2+$3+$4+$5;}
| action_body '{' action_body '}'
{$$ = $1+$2+$3+$4;}
;
%%
// transform ebnf to bnf if necessary
function extend (json, grammar) {
json.bnf = ebnf ? transform(grammar) : grammar;
return json;
}
## license
MIT
|
