feat: use more precise pi

with pretty_eval, I still get:
-9.194801691 * 10^-618

but at least that's more accurate than the prior:
1.224646799 * 10^-16

src/nodes/eval.rs

@@ -83,111 +83,41 @@ fn collapse_toplevel(nodes: &mut Vec<Node>, mut end: usize) -> Result<(), Error>
             return Err(Error::MissingArgument(node.clone()));
         };
 
-        function.for_float()(n);
+        function.apply_to(n);
 
         nodes.remove(start + index);
         end -= 1;
     }
 
-    while let Some(operator) = nodes[start..end]
-        .iter()
-        .position(|n| *n == Node::Operator(Operator::Exp))
-    {
-        let lhs = match nodes.remove(start + operator - 1) {
-            Node::Number(n) => n,
-            n => return Err(Error::InvalidOperand(n)),
-        };
-        end -= 1;
-        match nodes.get_mut(start + operator) {
-            None => return Err(Error::OutOfBounds(Nodes(nodes.clone()), start + operator)),
+    macro_rules! collapse_operator {
+        ($operator:expr) => {
+            while let Some(index) = nodes[start..end]
+                .iter()
+                .position(|n| *n == Node::Operator($operator))
+            {
+                let lhs = match nodes.remove(start + index - 1) {
+                    Node::Number(n) => n,
+                    n => return Err(Error::InvalidOperand(n)),
+                };
+                end -= 1;
+                match nodes.get_mut(start + index) {
+                    None => return Err(Error::OutOfBounds(Nodes(nodes.clone()), start + index)),
 
-            Some(Node::Number(n)) => n.pow_from(lhs),
-            Some(n) => return Err(Error::InvalidOperand(n.clone())),
-        };
+                    Some(Node::Number(n)) => $operator.apply_to(n, lhs),
+                    Some(n) => return Err(Error::InvalidOperand(n.clone())),
+                };
 
-        nodes.remove(start + operator - 1);
-        end -= 1;
+                nodes.remove(start + index - 1);
+                end -= 1;
+            }
+        };
     }
 
-    while let Some(operator) = nodes[start..end]
-        .iter()
-        .position(|n| *n == Node::Operator(Operator::Div))
-    {
-        let lhs = match nodes.remove(start + operator - 1) {
-            Node::Number(n) => n,
-            n => return Err(Error::InvalidOperand(n)),
-        };
-        end -= 1;
-        match nodes.get_mut(start + operator) {
-            None => return Err(Error::OutOfBounds(Nodes(nodes.clone()), start + operator)),
-
-            Some(Node::Number(n)) => n.div_from(lhs),
-            Some(n) => return Err(Error::InvalidOperand(n.clone())),
-        };
-
-        nodes.remove(start + operator - 1);
-        end -= 1;
-    }
-
-    while let Some(operator) = nodes[start..end]
-        .iter()
-        .position(|n| *n == Node::Operator(Operator::Mult))
-    {
-        let lhs = match nodes.remove(start + operator - 1) {
-            Node::Number(n) => n,
-            n => return Err(Error::InvalidOperand(n)),
-        };
-        end -= 1;
-        match nodes.get_mut(start + operator) {
-            None => return Err(Error::OutOfBounds(Nodes(nodes.clone()), start + operator)),
-
-            Some(Node::Number(n)) => n.mul_from(lhs),
-            Some(n) => return Err(Error::InvalidOperand(n.clone())),
-        };
-
-        nodes.remove(start + operator - 1);
-        end -= 1;
-    }
-
-    while let Some(operator) = nodes[start..end]
-        .iter()
-        .position(|n| *n == Node::Operator(Operator::Minus))
-    {
-        let lhs = match nodes.remove(start + operator - 1) {
-            Node::Number(n) => n,
-            n => return Err(Error::InvalidOperand(n)),
-        };
-        end -= 1;
-        match nodes.get_mut(start + operator) {
-            None => return Err(Error::OutOfBounds(Nodes(nodes.clone()), start + operator)),
-
-            Some(Node::Number(n)) => n.sub_from(lhs),
-            Some(n) => return Err(Error::InvalidOperand(n.clone())),
-        };
-
-        nodes.remove(start + operator - 1);
-        end -= 1;
-    }
-
-    while let Some(operator) = nodes[start..end]
-        .iter()
-        .position(|n| *n == Node::Operator(Operator::Plus))
-    {
-        let lhs = match nodes.remove(start + operator - 1) {
-            Node::Number(n) => n,
-            n => return Err(Error::InvalidOperand(n)),
-        };
-        end -= 1;
-        match nodes.get_mut(start + operator) {
-            None => return Err(Error::OutOfBounds(Nodes(nodes.clone()), start + operator)),
-
-            Some(Node::Number(n)) => n.add_from(lhs),
-            Some(n) => return Err(Error::InvalidOperand(n.clone())),
-        };
-
-        nodes.remove(start + operator - 1);
-        end -= 1;
-    }
+    collapse_operator!(Operator::Exp);
+    collapse_operator!(Operator::Div);
+    collapse_operator!(Operator::Mult);
+    collapse_operator!(Operator::Minus);
+    collapse_operator!(Operator::Plus);
 
     if nodes.len() > 1 {
         nodes.remove(end);
@@ -197,21 +127,32 @@ fn collapse_toplevel(nodes: &mut Vec<Node>, mut end: usize) -> Result<(), Error>
     Ok(())
 }
 
-impl Function {
-    fn for_float(&self) -> impl FnMut(&mut Float) {
+impl Operator {
+    fn apply_to(&self, rhs: &mut Float, lhs: Float) {
         match self {
-            Function::Sqrt => Float::sqrt_mut,
+            Self::Plus => Float::add_from(rhs, lhs),
+            Self::Minus => Float::sub_from(rhs, lhs),
+            Self::Mult => Float::mul_from(rhs, lhs),
+            Self::Div => Float::div_from(rhs, lhs),
+            Self::Exp => Float::pow_from(rhs, lhs),
+        }
+    }
+}
+impl Function {
+    fn apply_to(&self, n: &mut Float) {
+        match self {
+            Self::Sqrt => Float::sqrt_mut(n),
 
-            Function::Ln => Float::ln_mut,
+            Self::Ln => Float::ln_mut(n),
 
-            Function::Sine => Float::sin_mut,
-            Function::ArcSine => Float::asin_mut,
-            Function::Cosine => Float::cos_mut,
-            Function::ArcCosine => Float::acos_mut,
-            Function::Tangent => Float::tan_mut,
-            Function::ArcTangent => Float::atan_mut,
-            Function::Secant => Float::sec_mut,
-            Function::CoSecant => Float::csc_mut,
+            Self::Sine => Float::sin_mut(n),
+            Self::ArcSine => Float::asin_mut(n),
+            Self::Cosine => Float::cos_mut(n),
+            Self::ArcCosine => Float::acos_mut(n),
+            Self::Tangent => Float::tan_mut(n),
+            Self::ArcTangent => Float::atan_mut(n),
+            Self::Secant => Float::sec_mut(n),
+            Self::CoSecant => Float::csc_mut(n),
         }
     }
 }

src/nodes/parse.rs

@@ -1,7 +1,10 @@
 use core::f64;
 use std::str::FromStr;
 
-use rug::{Float, float::ParseFloatError};
+use rug::{
+    Float,
+    float::{self, ParseFloatError},
+};
 
 use crate::nodes::{Function, Node, Nodes, Operator};
 
@@ -10,7 +13,7 @@ impl Node {
         Ok(match s {
             "c" => Self::from(299_792_458),
             "A" => Self::from(6.02214076e23),
-            "pi" | "π" => Self::from(f64::consts::PI),
+            "pi" | "π" => Self::from(float::Constant::Pi),
             // Planck's constant, in J*s (joule-seconds)
             "h" => Self::from(6.62607015e-34),
             "e" => Self::from(f64::consts::E),

src/nodes/tests.rs

@@ -51,3 +51,8 @@ fn constant_implicit_mult() {
     assert_eq!(eval("2pi"), 6.283185307179586);
     assert_eq!(eval("pi2"), 6.283185307179586);
 }
+
+#[test]
+fn pi_precision() {
+    assert_eq!(eval("sin(pi)"), 0.)
+}