This is temporary specification.
There's two block on toplevel. one is 'class' block, another is 'user code' block. 'user code' block MUST places after 'class' block.
You can insert comment about all places. Two style comment can be used, Ruby style (#.....) and C style (/*......*/) .
class block is like this:
class class_name
[precedance table]
[token declearations]
[expected number of S/R conflict]
[options]
[semantic value convertion]
[start rule]
rule
RULES
end
class_name is a name of parser class.
This is the name of generating parser class.
If class_name includes '::', Racc outputs module clause. For example, "class M::C" causes creating the code bellow:
module M
class C
:
end
end
'rule block' discripts grammar which is able to be understood by parser. For example:
(token): (token) (token) (token).... (action) ;
(token): (token) (token) (token).... (action)
| (token) (token) (token).... (action)
| (token) (token) (token).... (action)
(action) is an action which is executed when its (token)s are found.
(action) is like this:
{ print val[0]
puts val[1] }
In (action), you cannot use '%' string, here document, '%r' regexp.
Actions can be omitted. When it is omitted, ''(empty string) is used.
A return value of action is a value of left side value ($$). It is value of result, or returned value by "return" statement.
Then, here's a sample of whole 'rule block'.
rule
goal: definition ruls source { result = val }
definition: /* none */ { result = [] }
| definition startdesig { result[0] = val[1] }
| definition
precrule # this line continue from upper line
{
result[1] = val[1]
}
startdesig: START TOKEN
end
You can use these special local variables in action.
This function is equal to '%prec' in yacc. To designate this block:
prechigh
nonassoc '++'
left '*' '/'
left '+' '-'
right '='
preclow
'right' is '%right', 'left' is '%left'. While this example is written
'prechigh' upper and 'preclow' lower, another format 'preclow...prechigh'
is also OK.
'%prec' can be used. format is like this:
prechigh
nonassoc UMINUS
left '*' '/'
left '+' '-'
preclow
rule
exp: exp '*' exp
| exp '-' exp
| '-' exp = UMINUS # this!!!
:
Racc has bison's "expect" directive.
# Example
class MyParser
rule
expect 3
:
This directive declears "expected" number of shift/reduce conflict.
If "expected" number is equal to real number, racc does not print
confliction warning message. Mainly for release-version parser.
By declearing tokens that IT IS TOKEN, you can avoid many meanless bugs.
If decleared token does not exist/existing token does not decleared,
Racc output warnings.
Declearation syntax is:
token TOKEN_NAME AND_IS_THIS
ALSO_THIS_IS AGAIN_AND_AGAIN THIS_IS_LAST
You can write options for racc command in your racc file.
options OPTION OPTION ...Now options are:
Token symbols are, as default,
convert
PLUS 'PlusClass' # not use :PLUS but PlusClass
MIN 'MinusClass' # not use :MIN but MinusClass
end
Almost all ruby value can be used by token symbol,
but 'false' and 'nil' are NOT. These are causes unexpected parse error.
If you want to use String as token symbol, special care is required. For example:
convert
class '"cls"' # in code, "cls"
PLUS '"plus\n"' # in code, "plus\n"
MIN "\"minus#{val}\"" # in code, \"minus#{val}\"
end
This is not BUG, but FEATURE.
'%start' in yacc. This changes start rule.
start real_target
this statement won't be used forever, I think.
'user block' is Ruby source code which is copied to output.
In racc command, Three spetial user code
'header' 'inner' 'footer' are used.
Until version 0.10.2, they are called prepare/inner/driver.
It is also OK, but they will be eliminated in future.
format of user code is like this:
---- header
ruby statement
ruby statement
ruby statement
---- inner
ruby statement
:
If 4 '-' exist on line head, racc treat it as beginning of user code.
A name of user code must be one word.
You can include other file as user code like this:
---- footer = init.rb run.rb print 'this code is executed too.'This statement makes racc to use "init.rb" "run.rb" as 'footer' user code.
Copyright (c) 1999-2001 Minero Aoki <aamine@loveruby.net>