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设定一个目标。在原有的框架上实现Rail类型。这是最最最基本的数据载体，基本得以至于拿它命名这个语言。

测试项

代码先这么写，想好期望的目标。

fn main() {test(String::from(r"
a1 = b1
a2 = b2
+ c1a3 = b3a4 = b4a5 = b5+ c2a6 = b6+ c3a7 = b7+ c4
"));
}

构建思路

在into_tokens()之前不需要改动，因为词法分析和语言无关。
其实很简单，只要追踪Comment就知道代码往哪加了。这是在Rail之前构建Comment得唯一原因。
无脑乱写，最终的测试代码如下。

use std::mem;const OMMISION: &str = "/";
const CATEGORY: &str = "+";
const RAIL: &str = "=";#[derive(Debug, Clone)]
enum Line {PlaceHolder,Comment { content: String },Rail { name: String, content: String },Category { name: String },
}#[derive(Debug)]
enum Node {PlaceHolder,Comment { content: String },Rail { name: String, content: String },Domain { category: Line, rails: Vec<Node> },
}struct Root {name: String,rails: Vec<Node>,
}fn into_tokens(lines_input: &str) -> (Vec<Vec<String>>, Vec<usize>) {let mut word_current = String::new();let mut line_current = Vec::new();let mut lines_list_splited = Vec::new();let mut indent_current = 0;let mut indent_list = Vec::new();let mut indent_state_in = true;for char in lines_input.chars() {match char {'\n' => {if !word_current.is_empty() {line_current.push(word_current.clone());word_current.clear();}if !line_current.is_empty() {lines_list_splited.push(line_current.clone());indent_list.push(indent_current);}line_current.clear();indent_current = 0;indent_state_in = true;}' ' => {if indent_state_in {indent_current += 1;} else if !word_current.is_empty() {line_current.push(word_current.clone());word_current.clear();}}other => {indent_state_in = false;word_current.push(other);}}}if !word_current.is_empty() {line_current.push(word_current);}if !line_current.is_empty() {lines_list_splited.push(line_current);indent_list.push(indent_current);}let indent_list = indent_list.into_iter().map(|x| x / 2).collect();(lines_list_splited, indent_list)
}fn trim_lines(lines: &mut Vec<Vec<String>>) {let trim = |s: &str| -> String {let mut result = String::new();let mut chars = s.chars().peekable();while let Some(c) = chars.next() {if c == '\\' {match chars.peek() {Some('_') => {chars.next();result.push(' ');}Some('\\') => {chars.next();result.push('\\');}_ => result.push(c),}} else {result.push(c);}}result};for line in lines {for word in line.iter_mut() {*word = trim(word);}}
}fn into_lines(token_list: &Vec<Vec<String>>, range: usize) -> Vec<Line> {let mut local = Vec::new();for i in 0..range {let token = &token_list[i];let lenth = token.len();let data = match lenth {1 => match token[0].as_str() {OMMISION => Line::PlaceHolder,_ => continue,},2 => match token[0].as_str() {OMMISION => Line::Comment { content: token[1].clone() },CATEGORY => Line::Category { name: token[1].clone() },_ => continue,},3 => match token[1].as_str() {RAIL => Line::Rail { name: token[0].clone(), content: token[2].clone() },_ => continue}_ => continue,};local.push(data);}local
}fn into_nodes(domain_name: &str, indent_list: Vec<usize>, line_list: Vec<Line>, range: usize) -> Root {let mut root = Root { name: domain_name.to_string(), rails: Vec::new() };let mut stack: Vec<Vec<Node>> = vec![vec![]];let mut context = 0;for i in 0..range {let indent = indent_list[i];let indent_move = indent as isize - context as isize;let line = &line_list[i];if indent_move < 0 {for _ in 0..-indent_move {if let Some(child_layer) = stack.pop() {if let Some(parent_layer) = stack.last_mut() {if let Some(Node::Domain { rails, .. }) = parent_layer.last_mut() {*rails = child_layer;}}}}}let node = match line {Line::PlaceHolder => Node::PlaceHolder,Line::Comment { content } => Node::Comment { content: content.clone() },Line::Rail { name, content } => Node::Rail { name: name.clone(), content: content.clone()},Line::Category { name } => Node::Domain {category: Line::Category { name: name.clone() },rails: Vec::new(),},};if indent_move > 0 {if let Some(current_layer) = stack.last_mut() {if let Some(Node::Domain { rails, .. }) = current_layer.last_mut() {let new_layer = mem::take(rails);stack.push(new_layer);}}}if let Some(current_layer) = stack.last_mut() {current_layer.push(node);}context = indent;}while let Some(child_layer) = stack.pop() {if let Some(parent_layer) = stack.last_mut() {if let Some(Node::Domain { rails, .. }) = parent_layer.last_mut() {*rails = child_layer;}} else {root.rails = child_layer;}}root
}fn print_node(node: &Node, indent: usize) {let indent_str = "_".repeat(indent);match node {Node::PlaceHolder => println!("{indent_str}/"),Node::Comment { content } => println!("{indent_str}/ {}", content),Node::Rail { name, content } => println!("{indent_str}{} = {}", name, content),Node::Domain { category, rails } => {match category {Line::Category { name } => println!("{indent_str}+ {}", name),_ => {}}for child in rails {print_node(child, indent + 2);}}}
}fn check_nodes(root: &Root) {println!("[{}]", root.name);for node in &root.rails {print_node(node, 0);}
}fn main() {test(String::from(r"
a1 = b1
a2 = b2
+ c1a3 = b3a4 = b4a5 = b5+ c2a6 = b6+ c3a7 = b7+ c4
"));
}fn test(input: String) {let (mut line_list, indent_list) = into_tokens(&input);trim_lines(&mut line_list);let range = line_list.len();let lines = into_lines(&line_list, range);let root = into_nodes("local", indent_list, lines, range);check_nodes(&root);
}

测试结果与预期一致。

[local]
a1 = b1
a2 = b2
+ c1
__a3 = b3
__a4 = b4
__a5 = b5
__+ c2
____a6 = b6
____+ c3
__a7 = b7
__+ c4