在没有左手递归的情况下解析布尔表达式

Question

我想要匹配这个

f(some_thing) == 'something else'

• f(some_thing)是一个函数调用,它是一个表达式
• ==是一个布尔运算符
• 'something else'是一个字符串,也是一个表达式

所以布尔表达式应该是

expression operator expression

问题是我无法弄清楚如何在不离开递归的情况下做到这一点这些是我的规则

expression 
  = 
  bool_expression
  / function_call
  / string
  / real_number
  / integer
  / identifier

bool_expression
  = l:expression space* op:bool_operator space* r:expression 
  { return ... }

使用语法符号,我有

O := ==|<=|>=|<|>|!=  // operators
E := B|....           // expression, many non terminals
B := EOE

因为我的语法是EOE,我不知道如何使用左手算法

A := Ab|B
transforms into
A := BA'
A':= e|bA

其中e为空,b为终端

Answer 1

像这样的东西应该这样做:

expression
 = bool_expression

bool_expression
 = add_expression "==" bool_expression
 / add_expression "!=" bool_expression
 / add_expression

add_expression
 = mult_expression "+" add_expression
 / mult_expression "-" add_expression
 / mult_expression

mult_expression
 = atom "*" mult_expression
 / atom "/" mult_expression
 / atom

atom
 = function_call 
 / string
 / real_number
 / integer
 / identifier

function_call
 = identifier "(" (expression ("," expression)*)? ")"

string
 = "'" [^']* "'"

identifier
 = [a-zA-Z_]+

integer
 = [0-9]+

real_number
 = integer "." integer?
 / "." integer