Implement Expression printing
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@@ -4,3 +4,4 @@ pub mod binding;
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pub mod lex;
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pub mod parse;
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pub mod print;
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+389
@@ -0,0 +1,389 @@
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use crate::expression::Expression;
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use crate::binding::{Binding, Power};
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#[derive(Clone, Copy, Debug)]
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enum Position {
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Left,
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Right,
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}
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impl Position {
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fn binds(&self, a: Binding, b: Binding) -> bool
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{
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match self {
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Position::Left => b <= a,
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Position::Right => a >= b,
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}
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}
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}
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impl std::fmt::Display for Expression {
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fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
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print(f, self, Binding::left(Power::Minimum), Position::Left)
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}
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}
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fn print(
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f: &mut std::fmt::Formatter<'_>,
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expr: &Expression,
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limit: Binding,
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position: Position) -> std::fmt::Result {
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let binding = Binding::of_expression(expr);
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if position.binds(binding, limit) {
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print_dispatch(f, expr, binding)
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} else {
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write!(f, "(")?;
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print_dispatch(f, expr, binding)?;
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write!(f, ")")
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}
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}
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fn print_dispatch(
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f: &mut std::fmt::Formatter<'_>,
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expr: &Expression,
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limit: Binding) -> std::fmt::Result {
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match expr {
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Expression::Integer(x) => write!(f, "{}", x),
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Expression::Symbol(c) => write!(f, "{}", c),
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Expression::Sum(x, y) => print_sum(f, x, y, limit),
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Expression::Difference(x, y) => print_difference(f, x, y, limit),
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Expression::Product(x, y) => print_product(f, x, y, limit),
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Expression::Quotient(x, y) => print_quotient(f, x, y, limit),
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Expression::Exponent(x, y) => print_exponent(f, x, y, limit),
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}
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}
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fn print_sum(
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f: &mut std::fmt::Formatter<'_>,
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x: &Expression,
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y: &Expression,
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limit: Binding) -> std::fmt::Result {
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print(f, x, limit, Position::Left)?;
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write!(f, " + ")?;
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print(f, y, limit, Position::Right)
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}
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fn print_difference(
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f: &mut std::fmt::Formatter<'_>,
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x: &Expression,
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y: &Expression,
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limit: Binding) -> std::fmt::Result {
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print(f, x, limit, Position::Left)?;
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write!(f, " - ")?;
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print(f, y, limit, Position::Right)
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}
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fn print_product(
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f: &mut std::fmt::Formatter<'_>,
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x: &Expression,
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y: &Expression,
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limit: Binding) -> std::fmt::Result {
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print(f, x, limit, Position::Left)?;
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let y_string = print_to_string(y, limit, Position::Right);
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if y_string.starts_with(is_numerical) {
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write!(f, "*{}", y_string)
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} else {
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write!(f, "{}", y_string)
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}
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}
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fn print_quotient(
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f: &mut std::fmt::Formatter<'_>,
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x: &Expression,
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y: &Expression,
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limit: Binding) -> std::fmt::Result {
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print(f, x, limit, Position::Left)?;
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write!(f, "/")?;
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print(f, y, limit, Position::Right)
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}
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fn print_exponent(
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f: &mut std::fmt::Formatter<'_>,
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x: &Expression,
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y: &Expression,
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limit: Binding) -> std::fmt::Result {
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print(f, x, limit, Position::Left)?;
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write!(f, "^")?;
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print(f, y, limit, Position::Right)
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}
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fn print_to_string(x: &Expression, lim: Binding, pos: Position) -> String {
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std::fmt::from_fn(|f| print(f, x, lim, pos)).to_string()
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}
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fn is_numerical(c: char) -> bool {
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c.is_ascii_digit() || c == '-'
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}
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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 integer_1_is_printed_as_1() {
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let expr = Expression::Integer(1);
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assert_eq!(expr.to_string(), "1");
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}
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#[test]
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fn symbol_x_is_printed_as_x() {
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let expr = Expression::Symbol('x');
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assert_eq!(expr.to_string(), "x");
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}
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#[test]
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fn sum_x_y_is_printed_as_x_plus_y() {
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let expr = Expression::sum(
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Expression::Symbol('x'),
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Expression::Symbol('y'));
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assert_eq!(expr.to_string(), "x + y");
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}
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#[test]
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fn difference_x_y_is_printed_as_x_minus_y() {
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let expr = Expression::difference(
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Expression::Symbol('x'),
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Expression::Symbol('y'));
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assert_eq!(expr.to_string(), "x - y");
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}
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#[test]
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fn product_x_y_is_printed_as_xy() {
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let expr = Expression::product(
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Expression::Symbol('x'),
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Expression::Symbol('y'));
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assert_eq!(expr.to_string(), "xy");
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}
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#[test]
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fn product_1_2_is_printed_as_1_times_2() {
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let expr = Expression::product(
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Expression::Integer(1),
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Expression::Integer(2));
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assert_eq!(expr.to_string(), "1*2");
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}
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#[test]
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fn quotient_x_y_is_printed_as_x_slash_y() {
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let expr = Expression::quotient(
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Expression::Symbol('x'),
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Expression::Symbol('y'));
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assert_eq!(expr.to_string(), "x/y");
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}
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#[test]
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fn exponent_x_y_is_printed_as_x_caret_y() {
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let expr = Expression::exponent(
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Expression::Symbol('x'),
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Expression::Symbol('y'));
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assert_eq!(expr.to_string(), "x^y");
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}
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#[test]
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fn product_of_sums_prints_with_parens() {
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let expr = Expression::product(
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Expression::sum(
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Expression::Symbol('a'),
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Expression::Symbol('b')),
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Expression::sum(
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Expression::Symbol('c'),
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Expression::Symbol('d')));
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assert_eq!(expr.to_string(), "(a + b)(c + d)");
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}
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#[test]
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fn sum_of_products_prints_without_parens() {
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let expr = Expression::sum(
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Expression::product(
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Expression::Symbol('a'),
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Expression::Symbol('b')),
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Expression::product(
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Expression::Symbol('c'),
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Expression::Symbol('d')));
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assert_eq!(expr.to_string(), "ab + cd");
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}
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#[test]
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fn sum_of_sum_x_y_and_z_prints_without_parens() {
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let expr = Expression::sum(
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Expression::sum(
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Expression::Symbol('x'),
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Expression::Symbol('y')),
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Expression::Symbol('z'));
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assert_eq!(expr.to_string(), "x + y + z");
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}
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#[test]
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fn sum_x_sum_y_z_prints_without_parens() {
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let expr = Expression::sum(
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Expression::Symbol('x'),
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Expression::sum(
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Expression::Symbol('y'),
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Expression::Symbol('z')));
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assert_eq!(expr.to_string(), "x + y + z");
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}
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#[test]
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fn product_of_product_x_y_and_z_prints_without_parens() {
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let expr = Expression::product(
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Expression::product(
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Expression::Symbol('x'),
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Expression::Symbol('y')),
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Expression::Symbol('z'));
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assert_eq!(expr.to_string(), "xyz");
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}
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#[test]
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fn product_x_product_y_z_prints_without_parens() {
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let expr = Expression::product(
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Expression::Symbol('x'),
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Expression::product(
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Expression::Symbol('y'),
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Expression::Symbol('z')));
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assert_eq!(expr.to_string(), "xyz");
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}
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#[test]
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fn difference_of_difference_x_y_and_z_prints_without_parens() {
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let expr = Expression::difference(
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Expression::difference(
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Expression::Symbol('x'),
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Expression::Symbol('y')),
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Expression::Symbol('z'));
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assert_eq!(expr.to_string(), "x - y - z");
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}
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#[test]
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fn difference_x_difference_y_z_prints_with_parens() {
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let expr = Expression::difference(
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Expression::Symbol('x'),
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Expression::difference(
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Expression::Symbol('y'),
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Expression::Symbol('z')));
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assert_eq!(expr.to_string(), "x - (y - z)");
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}
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#[test]
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fn quotient_of_quotient_x_y_and_z_prints_without_parens() {
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let expr = Expression::quotient(
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Expression::quotient(
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Expression::Symbol('x'),
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Expression::Symbol('y')),
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Expression::Symbol('z'));
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assert_eq!(expr.to_string(), "x/y/z");
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}
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#[test]
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fn quotient_x_quotient_y_z_prints_with_parens() {
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let expr = Expression::quotient(
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Expression::Symbol('x'),
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Expression::quotient(
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Expression::Symbol('y'),
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Expression::Symbol('z')));
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assert_eq!(expr.to_string(), "x/(y/z)");
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}
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#[test]
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fn exponent_x_exponent_y_z_prints_without_parens() {
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let expr = Expression::exponent(
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Expression::Symbol('x'),
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Expression::exponent(
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Expression::Symbol('y'),
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Expression::Symbol('z')));
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assert_eq!(expr.to_string(), "x^y^z");
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}
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#[test]
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fn exponent_of_exponent_x_y_and_z_prints_with_parens() {
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let expr = Expression::exponent(
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Expression::exponent(
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Expression::Symbol('x'),
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Expression::Symbol('y')),
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Expression::Symbol('z'));
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assert_eq!(expr.to_string(), "(x^y)^z");
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}
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#[test]
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fn complex_expression_1() {
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let expr = Expression::difference(
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Expression::product(
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Expression::Integer(2),
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Expression::exponent(
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Expression::Symbol('x'),
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Expression::Integer(3))),
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Expression::quotient(
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Expression::Symbol('y'),
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Expression::exponent(
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Expression::Symbol('z'),
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Expression::Integer(2))));
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assert_eq!(expr.to_string(), "2x^3 - y/z^2");
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}
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#[test]
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fn complex_expression_2() {
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let expr = Expression::sum(
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Expression::product(
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Expression::Symbol('x'),
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Expression::difference(
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Expression::sum(
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Expression::Symbol('x'),
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Expression::Symbol('y')),
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Expression::Integer(1))),
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Expression::exponent(
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Expression::Symbol('y'),
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Expression::difference(
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Expression::Integer(3),
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Expression::Symbol('x'))));
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assert_eq!(expr.to_string(), "x(x + y - 1) + y^(3 - x)");
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}
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#[test]
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fn product_1_product_2_3_is_printed_with_times() {
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let expr = Expression::product(
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Expression::Integer(1),
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Expression::product(
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Expression::Integer(2),
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Expression::Integer(3)));
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assert_eq!(expr.to_string(), "1*2*3");
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}
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#[test]
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fn product_1_product_2_x_is_printed_with_times() {
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let expr = Expression::product(
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Expression::Integer(1),
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Expression::product(
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Expression::Integer(2),
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Expression::Symbol('x'),));
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assert_eq!(expr.to_string(), "1*2x");
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}
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#[test]
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fn product_x_product_2_3_is_printed_with_times() {
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let expr = Expression::product(
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Expression::Symbol('x'),
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Expression::product(
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Expression::Integer(2),
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Expression::Integer(3)));
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assert_eq!(expr.to_string(), "x*2*3");
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}
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#[test]
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fn product_1_minus_2_is_printed_with_times() {
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let expr = Expression::product(
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Expression::Integer(1),
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Expression::Integer(-2));
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assert_eq!(expr.to_string(), "1*-2");
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}
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#[test]
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fn product_sum_1_2_sum_3_3_is_printed_without_times() {
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let expr = Expression::product(
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Expression::sum(
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Expression::Integer(1),
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Expression::Integer(2)),
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Expression::sum(
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Expression::Integer(3),
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Expression::Integer(4)));
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assert_eq!(expr.to_string(), "(1 + 2)(3 + 4)");
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}
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}
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