llvm cookbook 2.1 定义语法

实现词法分析器和语法分析器之前，需要先定义我们将要实现的语言的语法。

一个语言通常包含了变量、函数调用和常量等。为了简便，我们只有32位整数的数值常量，同时，变量是无类型的。

1 numeric expression

numeric_expr := number

2 parenthesis expression

paran_expr := '(' expression ')'

3 identifier expression

identifier_expr := identifier
identifier_expr := identifier '(' expr_list ')'

4

expr_list := (empty)
expr_list := expression (',' expression)*

5 primary expression

primary := identifier_expr
primary := numeric_expr
primary := paran_expr

6 expression can lead to binary expression

 expression := primary binoprhs

7 binary expression with RHS can yield combinations of binary operators and expressions

binoprhs := ( binoperator primary)*
binoperator := '+' / '-' / '*' / '/'

8 function declaration

func_decl := identifier '(' identifier_list ')'
identifier_list := (empty)
identifier_list := (identifier)*

9 function definition

function_defn := 'def' func_decl expression

10 top level expression

toplevel_expr := expression

示例

def foo (x, y)
 x + y * 16