I am working on writing a rust implementation of a sh-like language.
Rather than posting 600 lines of code here, you can just go to the GitHub repository.
Is this a good approach for lexxing?
Here's the lex function:
pub fn lex(&mut self) {
while self.input.has_next() {
let c: char = self.input.next();
match c {
/// Any whitespace is ignored.
' ' | '\t' | '\n' | '\r' => {
continue;
}
/// Comments can also be ignored.
'#' => {
while self.input.has_next() && self.input.next() != '\n' {
self.input.next();
}
continue;
}
// Redirection
'>' => {
if self.input.has_next() {
match self.input.lookahead(1) {
'>' => {
self.input.next();
self.output.push(Token::new(TokenType::RedirAppend));
}
'|' => {
self.input.next();
self.output.push(Token::new(TokenType::ForceRedir));
}
_ => {
// We shouldn't eat the next token if it's anything else,
// it just means that the code either has a space afterwords
// or it's (potentially) important text
self.output.push(Token::new(TokenType::Redir));
}
}
}
}
// Pipes
'|' => {
self.output.push(Token::new(TokenType::Pipe));
}
'{' => {
self.output.push(Token::new(TokenType::LeftCurlyBrace));
}
'}' => {
self.output.push(Token::new(TokenType::RightCurlyBrace));
}
'[' => {
if self.input.has_next() && self.input.lookahead(1) == '[' {
self.input.next();
self.output
.push(Token::new(TokenType::LeftDoubleSquareBracket));
} else {
self.output.push(Token::new(TokenType::LeftSquareBracket));
}
}
']' => {
if self.input.has_next() && self.input.lookahead(1) == ']' {
self.input.next();
self.output
.push(Token::new(TokenType::RightDoubleSquareBracket));
} else {
self.output.push(Token::new(TokenType::RightSquareBracket));
}
}
'(' => {
if self.input.has_next() && self.input.lookahead(1) == '(' {
self.input.next();
self.output.push(Token::new(TokenType::LeftDoubleParen));
} else {
self.output.push(Token::new(TokenType::LeftParen));
}
}
')' => {
if self.input.has_next() && self.input.lookahead(1) == ')' {
self.input.next();
self.output.push(Token::new(TokenType::RightDoubleParen));
} else {
self.output.push(Token::new(TokenType::RightParen));
}
}
// Keywords and identifiers
'a'..='z' | 'A'..='Z' | '_' => {
if self.input.has_next_multi(3)
&& c == 'c'
&& self.input.lookahead_multi(3) == "ase"
{
self.input.next();
self.input.next();
self.output.push(Token::new(TokenType::Case));
} else if self.input.has_next_multi(5)
&& c == 'c'
&& self.input.lookahead_multi(5) == "oproc"
{
self.input.next();
self.input.next();
self.input.next();
self.input.next();
self.input.next();
self.output.push(Token::new(TokenType::Coproc));
} else if self.input.has_next() && c == 'd' && self.input.lookahead(1) == 'o' {
self.input.next();
self.output.push(Token::new(TokenType::Do));
} else if self.input.has_next_multi(3)
&& c == 'd'
&& self.input.lookahead_multi(3) == "one"
{
self.input.next();
self.input.next();
self.input.next();
self.output.push(Token::new(TokenType::Done));
} else if self.input.has_next_multi(3)
&& c == 'e'
&& self.input.lookahead_multi(3) == "lif"
{
self.input.next();
self.input.next();
self.input.next();
self.output.push(Token::new(TokenType::Elif));
} else if self.input.has_next_multi(3)
&& c == 'e'
&& self.input.lookahead_multi(3) == "lse"
{
self.input.next();
self.input.next();
self.input.next();
self.output.push(Token::new(TokenType::Else));
} else if self.input.has_next_multi(3)
&& c == 'e'
&& self.input.lookahead_multi(3) == "sac"
{
self.input.next();
self.input.next();
self.input.next();
self.output.push(Token::new(TokenType::Esac));
} else if self.input.has_next() && c == 'f' && self.input.lookahead(1) == 'i' {
self.input.next();
self.output.push(Token::new(TokenType::Fi));
} else if self.input.has_next_multi(2)
&& c == 'f'
&& self.input.lookahead_multi(2) == "or"
{
self.input.next();
self.input.next();
self.output.push(Token::new(TokenType::For));
} else if self.input.has_next_multi(7)
&& c == 'f'
&& self.input.lookahead_multi(7) == "unction"
{
self.input.next();
self.input.next();
self.input.next();
self.input.next();
self.input.next();
self.input.next();
self.input.next();
self.output.push(Token::new(TokenType::Function));
} else if self.input.has_next() && c == 'i' && self.input.lookahead(1) == 'f' {
self.input.next();
self.output.push(Token::new(TokenType::If));
} else if self.input.has_next() && c == 'i' && self.input.lookahead(1) == 'n' {
self.input.next();
self.output.push(Token::new(TokenType::In));
} else if self.input.has_next_multi(5)
&& c == 's'
&& self.input.lookahead_multi(5) == "elect"
{
self.input.next();
self.input.next();
self.input.next();
self.input.next();
self.input.next();
self.output.push(Token::new(TokenType::Select));
} else if self.input.has_next_multi(3)
&& c == 't'
&& self.input.lookahead_multi(3) == "hen"
{
self.input.next();
self.input.next();
self.input.next();
self.output.push(Token::new(TokenType::Then));
} else if self.input.has_next_multi(3)
&& c == 't'
&& self.input.lookahead_multi(3) == "ime"
{
self.input.next();
self.input.next();
self.input.next();
self.output.push(Token::new(TokenType::Time));
} else if self.input.has_next_multi(4)
&& c == 'u'
&& self.input.lookahead_multi(4) == "ntil"
{
self.input.next();
self.input.next();
self.input.next();
self.input.next();
self.output.push(Token::new(TokenType::Until));
} else if self.input.has_next_multi(4)
&& c == 'w'
&& self.input.lookahead_multi(4) == "hile"
{
self.input.next();
self.input.next();
self.input.next();
self.input.next();
self.output.push(Token::new(TokenType::While));
} else {
let mut tk: String = "".to_owned();
while self.input.has_next() {
match self.input.next() {
'a'..='z' | 'A'..='Z' | '_' | '0'..='9' => {
tk.push(c);
self.input.next();
}
_ => {
break;
}
}
self.output.push(Token::new(TokenType::Text));
}
}
}
_ => {
panic!("Can't handle character {}", c)
}
}
}
}
```
