broken state

src/output.rs

@@ -0,0 +1,66 @@
+use egg::{RecExpr, Id};
+use crate::language::EquationLanguage;
+
+// there is already a Display implementation generated by define_langauge!
+// but we want an alternative string conversion
+pub fn print_term(expr: &RecExpr<EquationLanguage>) -> String {
+	let root_id = Id::from(expr.as_ref().len()-1);
+	print_term_inner(expr, root_id).0
+}
+
+// the second result is the precedence of the top level op: 1 = '+-', 2 = '*/', 3 = '^', 4 = primitive
+fn print_term_inner(expr: &RecExpr<EquationLanguage>, id: Id) -> (String, usize) {
+	match &expr[id] {
+		EquationLanguage::Num(c) => {
+			(format!("{}", c), if c.denom == 1 { 4 } else { 2 })
+		},
+		EquationLanguage::Neg([a]) => {
+			(print_unary(expr, *a, "-", 1), 1)
+		},
+		EquationLanguage::Add([a,b]) => {
+			(print_binary(expr, *a, *b, "+", 1), 1)
+		},
+		EquationLanguage::Sub([a,b]) => {
+			(print_binary(expr, *a, *b, "-", 1), 1)
+		},
+		EquationLanguage::Mul([a,b]) => {
+			(print_binary(expr, *a, *b, "*", 2), 2)
+		},
+		EquationLanguage::Div([a,b]) => {
+			(print_binary(expr, *a, *b, "/", 2), 2)
+		},
+		EquationLanguage::Power([a,b]) => {
+			(print_binary(expr, *a, *b, "^", 3), 3)
+		},
+		_ => unimplemented!()
+	}
+}
+
+fn print_unary(expr: &RecExpr<EquationLanguage>, a: Id, op: &str, precedence: usize) -> String {
+	let (astr, aprec) = print_term_inner(expr, a);
+
+	if aprec > precedence {
+		format!("{}{}", op, astr)
+	} else {
+		format!("{}({})", op, astr)
+	}
+}
+
+fn print_binary(expr: &RecExpr<EquationLanguage>, a: Id, b: Id, op: &str, precedence: usize) -> String {
+	let (astr, aprec) = print_term_inner(expr, a);
+	let (bstr, bprec) = print_term_inner(expr, b);
+
+	if aprec > precedence {
+		if bprec > precedence {
+			format!("{} {} {}", astr, op, bstr)
+		} else {
+			format!("{} {} ({})", astr, op, bstr)
+		}
+	} else {
+		if bprec > precedence {
+			format!("({}) {} {}", astr, op, bstr)
+		} else {
+			format!("({}) {} ({})", astr, op, bstr)
+		}
+	}
+}