如何从野牛语法中初始化变量？

Question

let's imagine we have this grammar

start: 
expressions;
expressions:
           expressions expression 
           | expression 
           ;
expression:
          expression NAME value { float $2 = $3;}
          | NAME value  { float $1 = $2;}
          ;
value:
      INT '.' INT
      ;

and for this grammar we apply this input

a 2.0 b 3.0

this should be interpreted by our grammar like this ( float a = 2.0 ; float b = 3.0; )

my aim is really to declare some variable with a name and with a constructor do some thing like myClass NAME(value); and value is a float.

the problems are I don't know how to get the whole value of a grammatical bloc like value in my exemple and how to make a declaration of variable name that will change in each line with in input file and wont have some generic float a = $1;

I already have my flex tokeniser working which will give me NAME and VALUE

Answer 1

You can't use strings in place of variable names in C++. What you should do instead is to define a map from strings to floats and then do something like the_map[$2] = $3; instead of float $2 = $3; .

On an unrelated note, you need to add an action to value that makes it produce a float value (or make your lexer generate a single token for floats and use that). Otherwise $3 doesn't have a proper value when you use it in expression 's action.