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use super::error::ProgramError;
use super::Token;
pub type LexerResult = Result<Token, ProgramError>;
pub struct Lexer<'a> {
text: &'a str,
size: usize,
ptr: usize,
chr: Option<char>,
}
impl<'a> Lexer<'a> {
pub fn from(text: &str) -> Lexer {
Lexer {
text: &text,
size: text.len(),
ptr: 0,
chr: Some(text.as_bytes()[0] as char),
}
}
fn push_ptr(&mut self) {
self.ptr += 1;
if self.ptr < self.size {
self.chr = Some(self.text.as_bytes()[self.ptr] as char);
} else {
self.chr = None;
}
}
fn peek_ahead(&self, amt: &usize) -> String {
let mut result = String::new();
let next_ptr = self.ptr;
for pos in (next_ptr)..(next_ptr + amt) {
if pos < self.size {
result.push(self.text.as_bytes()[pos] as char);
} else {
break;
}
}
result
}
fn skip_whitespace(&mut self) {
while let Some(chr) = self.chr {
if chr.is_whitespace() {
self.push_ptr();
} else {
break;
}
}
}
fn build_integer(&mut self) -> usize {
let mut result = String::new();
while let Some(chr) = self.chr {
if chr.is_digit(10) {
result.push(self.chr.unwrap());
self.push_ptr();
} else {
break;
}
}
result.parse::<usize>().unwrap()
}
pub fn skip(&mut self, amt: usize) -> &mut Lexer<'a> {
for _ in 0..amt {
match self.next_token() {
_ => (),
};
}
self
}
pub fn next_token(&mut self) -> LexerResult {
while let Some(chr) = self.chr {
if chr.is_whitespace() {
self.skip_whitespace();
continue;
} else if chr.is_digit(10) {
return Ok(Token::NUMBER(self.build_integer()));
} else {
self.push_ptr();
match chr {
'+' => return Ok(Token::PLUS),
'-' => return Ok(Token::MINUS),
'*' => return Ok(Token::MULTIPLY),
'/' => return Ok(Token::DIVIDE),
'%' => return Ok(Token::MODULO),
'^' => return Ok(Token::EXPONENT),
'!' => return Ok(Token::FACTORIAL),
'.' => {
match self.peek_ahead(&1).as_ref() {
"/" => {
self.push_ptr();
return Ok(Token::DIVIDEINT);
}
_ => {
return Err(ProgramError::of(
"InvalidOperand",
"Invalid multi-character operand.",
))
}
}
}
'(' => return Ok(Token::LPAREN),
')' => return Ok(Token::RPAREN),
_ => {
return Err(ProgramError::of(
"InvalidCharacter",
"Expected Token, found unknown character.",
))
}
}
}
}
Ok(Token::EOF)
}
}