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use std::f64;
mod lex;
use crate::lex::*;
mod parse;
use crate::parse::*;
mod error;
use crate::error::{ CalcError, handler };
use rustyline::error::ReadlineError;
use rustyline::Editor;
fn main() {
let mut rl = Editor::<()>::new();
if rl.load_history("history.txt").is_err() {
println!("No previous history.");
}
'main: loop {
let readline = rl.readline("> ");
match readline {
Ok(line) => {
rl.add_history_entry(line.as_ref());
let evaled = eval_math_expression(&line[..]);
match evaled {
Ok(ans) => println!("{}", ans),
Err(e) => handler(e),
};
},
Err(ReadlineError::Interrupted) => {
println!("CTRL-C");
break
},
Err(ReadlineError::Eof) => {
println!("CTRL-D");
break
},
Err(err) => {
println!("Error: {:?}", err);
break
}
}
}
rl.save_history("history.txt").unwrap();
}
fn autobalance_parens(input: &str) -> Result<String, CalcError> {
let mut balanced = String::from(input);
let mut left_parens = 0;
let mut right_parens = 0;
for letter in input.chars() {
if letter == '(' {
left_parens += 1;
} else if letter == ')' {
right_parens += 1;
}
}
if left_parens > right_parens {
let extras = ")".repeat(left_parens - right_parens);
balanced.push_str(&extras[..]);
Ok(balanced)
} else if left_parens < right_parens {
return Err(CalcError::Syntax("Mismatched parentheses!".into()))
} else {
Ok(balanced)
}
}
fn eval_math_expression(input: &str) -> Result<f64, CalcError> {
let input = autobalance_parens(&input[..])?;
let lexed = lexer(&input[..])?;
let postfixed = to_postfix(lexed)?;
let evaled = eval_postfix(postfixed)?;
Ok(evaled)
}
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