Add WeibullError

src/distribution/mod.rs

@@ -34,7 +34,7 @@ pub use self::poisson::{Poisson, PoissonError};
 pub use self::students_t::{StudentsT, StudentsTError};
 pub use self::triangular::{Triangular, TriangularError};
 pub use self::uniform::{Uniform, UniformError};
-pub use self::weibull::Weibull;
+pub use self::weibull::{Weibull, WeibullError};
 
 mod bernoulli;
 mod beta;

src/distribution/weibull.rs

@@ -1,7 +1,7 @@
+use crate::consts;
 use crate::distribution::{Continuous, ContinuousCDF};
 use crate::function::gamma;
 use crate::statistics::*;
-use crate::{consts, Result, StatsError};
 use rand::Rng;
 use std::f64;
 
@@ -27,6 +27,26 @@ pub struct Weibull {
     scale_pow_shape_inv: f64,
 }
 
+#[derive(Copy, Clone, PartialEq, Eq, Debug, Hash)]
+pub enum WeibullError {
+    /// The shape is NaN, zero, or less than zero.
+    ShapeInvalid,
+
+    /// The scale is NaN, zero, or less than zero.
+    ScaleInvalid,
+}
+
+impl std::fmt::Display for WeibullError {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        match self {
+            WeibullError::ShapeInvalid => write!(f, "Shape is NaN, zero, or less than zero."),
+            WeibullError::ScaleInvalid => write!(f, "Scale is NaN, zero, or less than zero."),
+        }
+    }
+}
+
+impl std::error::Error for WeibullError {}
+
 impl Weibull {
     /// Constructs a new weibull distribution with a shape (k) of `shape`
     /// and a scale (λ) of `scale`
@@ -47,17 +67,20 @@ impl Weibull {
     /// result = Weibull::new(0.0, 0.0);
     /// assert!(result.is_err());
     /// ```
-    pub fn new(shape: f64, scale: f64) -> Result<Weibull> {
-        let is_nan = shape.is_nan() || scale.is_nan();
-        match (shape, scale, is_nan) {
-            (_, _, true) => Err(StatsError::BadParams),
-            (_, _, false) if shape <= 0.0 || scale <= 0.0 => Err(StatsError::BadParams),
-            (_, _, false) => Ok(Weibull {
-                shape,
-                scale,
-                scale_pow_shape_inv: scale.powf(-shape),
-            }),
+    pub fn new(shape: f64, scale: f64) -> Result<Weibull, WeibullError> {
+        if shape.is_nan() || shape <= 0.0 {
+            return Err(WeibullError::ShapeInvalid);
         }
+
+        if scale.is_nan() || scale <= 0.0 {
+            return Err(WeibullError::ScaleInvalid);
+        }
+
+        Ok(Weibull {
+            shape,
+            scale,
+            scale_pow_shape_inv: scale.powf(-shape),
+        })
     }
 
     /// Returns the shape of the weibull distribution