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55 lines
1.6 KiB
Rust
55 lines
1.6 KiB
Rust
/// This program contains list of valid AST nodes that can be constructed and also evaluates an AST to compute a value
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// Standard lib
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use std::error;
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//structs
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// List of allowed AST nodes that can be constructed by Parser
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// Tokens can be arithmetic operators or a Number
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#[derive(Debug, Clone, PartialEq)]
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pub enum Node {
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Add(Box<Node>, Box<Node>),
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Subtract(Box<Node>, Box<Node>),
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Multiply(Box<Node>, Box<Node>),
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Divide(Box<Node>, Box<Node>),
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Caret(Box<Node>, Box<Node>),
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Negative(Box<Node>),
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Number(f64),
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}
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// Given an AST, calculate the numeric value.
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pub fn eval(expr: Node) -> Result<f64, Box<dyn error::Error>> {
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use self::Node::*;
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match expr {
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Number(i) => Ok(i),
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Add(expr1, expr2) => Ok(eval(*expr1)? + eval(*expr2)?),
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Subtract(expr1, expr2) => Ok(eval(*expr1)? - eval(*expr2)?),
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Multiply(expr1, expr2) => Ok(eval(*expr1)? * eval(*expr2)?),
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Divide(expr1, expr2) => Ok(eval(*expr1)? / eval(*expr2)?),
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Negative(expr1) => Ok(-(eval(*expr1)?)),
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Caret(expr1, expr2) => Ok(eval(*expr1)?.powf(eval(*expr2)?)),
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}
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}
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//Unit tests
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn test_expr1() {
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use crate::parsemath::parser::Parser;
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let ast = Parser::new("1+2-3").unwrap().parse().unwrap();
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let value = eval(ast).unwrap();
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assert_eq!(value, 0.0);
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}
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#[test]
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fn test_expr2() {
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use crate::parsemath::parser::Parser;
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let ast = Parser::new("3+2-1*5/4").unwrap().parse().unwrap();
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let value = eval(ast).unwrap();
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assert_eq!(value, 3.75);
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}
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}
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