杰森语法问题，生成dparser产生的奇怪错误 [英] Issue with a Jison Grammar, Strange error from generate dparser
问题描述
我正在编写一个简单的Jison语法，以便在开始更复杂的项目之前获得一些经验.我尝试了一个简单的语法，该语法是用逗号分隔的数字范围列表，其中范围的开始和结束值相同，以使用单个数字的简写形式.但是，在某些测试输入上运行生成的解析器时，出现错误，这对我来说没有多大意义.这是我想出的语法:
/* description: Parses end executes mathematical expressions. */
/* lexical grammar */
%lex
%%
\s+ /* skip whitespace */
[0-9]+ {return 'NUMBER'}
"-" {return '-'}
"," {return ','}
<<EOF>> {return 'EOF'}
. {return 'INVALID'}
/lex
/* operator associations and precedence */
%start ranges
%% /* language grammar */
ranges
: e EOF
{return $1;}
;
e : rng { $$ = $1;}
| e ',' e {alert('e,e');$$ = new Array(); $$.push($1); $$.push($3);}
;
rng
: NUMBER '-' NUMBER
{$$ = new Array(); var rng = {Start:$1, End: $3; }; $$.push(rng); }
| NUMBER
{$$ = new Array(); var rng = {Start:$1, End: $1; }; $$.push(rng);}
;
NUMBER: {$$ = Number(yytext);};
测试输入为:
5-10,12-16
输出为:
Parse error on line 1:
5-10,12-16
^
Expecting '-', 'EOF', ',', got '8'
如果将'a'放在前面，我会发现关于查找"INVALID"的预期错误，但是我在输入字符串中没有"8"，所以我想知道这是否是内部状态吗?
我在以下位置使用在线解析器生成器: http://zaach.github.io/jison/尝试/
有什么想法?此产品使Jison感到困惑(它也使我感到困惑:)):
NUMBER: {$$ = Number(yytext);};
NUMBER应该是一个终端，但是上面的产生将其声明为一个空终端的非终端.因为它什么都不能匹配，所以它立即匹配，并且您的语法不允许两个连续的NUMBER.因此是错误.
此外，尽管我认为Jison的默认设置将解决此问题，但是您的语法是模棱两可的.不过，最好还是明确一点，因为这很容易.您的规则:
e : rng
| e ',' e
未指定,的关联"方式:换句话说，应将rng , rng , rng视为e , rng还是rng , e.第一个可能对您更好，因此您应该明确地编写它:
e : rng
| e ',' rng
以上内容的一大优点是，您无需在第二个产品中创建新的阵列；您只需将$3推到$1的末尾，然后将$$设置为$1.
I am writing a simple Jison grammar in order to get some experience before starting a more complex project. I tried a simple grammar which is a comma separated list of numeric ranges, with ranges where the beginning and ending values were the same to use a single number shorthand. However, when running the generated parser on some test input I get an error which doe snot make alot of sense to me. Here is the grammar i came up with:
/* description: Parses end executes mathematical expressions. */
/* lexical grammar */
%lex
%%
\s+ /* skip whitespace */
[0-9]+ {return 'NUMBER'}
"-" {return '-'}
"," {return ','}
<<EOF>> {return 'EOF'}
. {return 'INVALID'}
/lex
/* operator associations and precedence */
%start ranges
%% /* language grammar */
ranges
: e EOF
{return $1;}
;
e : rng { $$ = $1;}
| e ',' e {alert('e,e');$$ = new Array(); $$.push($1); $$.push($3);}
;
rng
: NUMBER '-' NUMBER
{$$ = new Array(); var rng = {Start:$1, End: $3; }; $$.push(rng); }
| NUMBER
{$$ = new Array(); var rng = {Start:$1, End: $1; }; $$.push(rng);}
;
NUMBER: {$$ = Number(yytext);};
The Test input is this:
5-10,12-16
The output is:
Parse error on line 1:
5-10,12-16
^
Expecting '-', 'EOF', ',', got '8'
If it put an 'a' at the front i get and expected error about finding "INVALID" but i dont have an "8" in the input string so i wondering if this is an internal state?
I am using the online parser generator at: http://zaach.github.io/jison/try/
thoughts?
This production is confusing Jison (and it confused me, too :) ):
NUMBER: {$$ = Number(yytext);};
NUMBER is supposed to be a terminal, but the above production declares it as a non-terminal with an empty body. Since it can match nothing, it immediately matches, and your grammar doesn't allow two consecutive NUMBERs. Hence the error.
Also, your grammar is ambiguous, although I suppose Jison's default will solve the issue. It would be better to be explicit, though, since it's easy. Your rule:
e : rng
| e ',' e
does not specify how , "associates": in other words, whether rng , rng , rng should be considered as e , rng or rng , e. The first one is probably better for you, so you should write it explicitly:
e : rng
| e ',' rng
One big advantage of the above is that you don't need to create a new array in the second production; you can just push $3 onto the end of $1 and set $$ to $1.
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