parser-stage 语法规范（同 step6）

program
    : function

function
    : type Identifier '(' ')' compound_statement
type
    : 'int'

compound_statement
    : '{' block_item* '}'

block_item
    : statement
    | declaration

statement
    : 'return' expression ';'
    | compound_statement
declaration
    : type Identifier ('=' expression)? ';'

expression
    : assignment

assignment
    : conditional
    | Identifier '=' expression

conditional
    : logical_or
    | logical_or '?' expression ':' conditional

logical_or
    : logical_and
    | logical_or '||' logical_and

logical_and
    : equality
    | logical_and '&&' equality

equality
    : relational
    | equality ('=='|'!=') relational

relational
    : additive
    | relational ('<'|'>'|'<='|'>=') additive

additive
    : multiplicative
    | additive ('+'|'-') multiplicative

multiplicative
    : unary
    | multiplicative ('*'|'/'|'%') unary

unary
    : primary
    | ('-'|'~'|'!') unary

primary
    : Integer
    | '(' expression ')'
    | Identifier