Internally, the parser code is generated by flex and bison. Those two
tools convert lexer.ll and parser.yy files into a number of .cc and .hh files.
To avoid adding flex and bison as dependencies, the result of the
- generation is checked into the github repo and is distributted in the
+ generation is checked into the github repository and is distributed in the
tarballs.
@section dhcpEvalLexer Lexer generation using flex
data into a series of tokens. It contains a small number of directives,
but the majority of the code consists of a definition of tokens. These
are regular expressions that define various tokens, e.g. strings,
- numbers, parentheses etc. Once the expression is matched, the associated
- code is called. In majority of the cases a generator method from
+ numbers, parentheses, etc. Once the expression is matched, the associated
+ action is executed. In majority of the cases a generator method from
@ref isc::eval::EvalParser is called. It returns newly created
bison tokens. The purpose of the lexer is to generate a stream
of tokens that are consumed by the parser.
lexer.cc and lexer.hh files must not be edited. In case there is a need
- to introduce changes, lexer.ll must be updated and the .cc .hh files
+ to introduce changes, lexer.ll must be updated and the .cc and .hh files
regenerated.
@section dhcpEvalParser Parser generation using bison
The actual definition of expression (lines 3-5) may either be a
single token or an expression token equals token. Token is further
defined in lines 7-15: it may either be a string (lines 8-11) or option
-(lines 12-15). When the actual case is defined, respective C++ code
-is called. For example, TokenString class is instantiated with
-appropriate values and put onto the expression stack.
+(lines 12-15). When the actual case is defined, respective C++ action
+is executed. For example, TokenString class is instantiated with
+appropriate values and put onto the expression vector.
@section dhcpEvalMakefile Generating parser files
Since the flex/bison tools are not necessary for a regular compilation,
there are checks conducted during configure, but lack of flex or
bison tools does not stop the configure process. There is a flag
- --enable-generate-parser that tells configure script that the
+ \--enable-generate-parser that tells configure script that the
parser will be generated. With this flag, the checks for flex/bison
are mandatory. Any missing or too old flex/bison will cause an
error.