Add CDF function

Cargo.toml

@@ -32,6 +32,7 @@ num = "0.4.1"
 num-bigint = "0.4.4"
 num-traits = "0.2.18"
 bigdecimal = "0.4.2"
+statrs = "0.18.0"
 
 [profile.release]
 opt-level = 3

README.md

@@ -142,6 +142,7 @@ There are many examples of processed expressions in the [integration test file](
     Ceil
     Round
     Exp
+    Cdf
 ```
 
 ## Built-in Defined Constants

src/lib.rs

@@ -103,6 +103,13 @@
 //! Log
 //! Abs
 //! Sqrt
+//! Max
+//! Min
+//! Floor
+//! Ceil
+//! Round
+//! Exp
+//! Cdf
 //! ```
 /// Parser
 pub mod parser;

src/rpn_resolver.rs

@@ -2,6 +2,7 @@ use crate::{
     parser::Parser,
     token::{self, MathFunction, Number, Operator, Token},
 };
+use statrs::distribution::{ContinuousCDF, Normal};
 use anyhow::anyhow;
 use log::debug;
 use std::{
@@ -200,6 +201,10 @@ impl RpnResolver<'_> {
                         MathFunction::Floor => f64::floor(value.into()),
                         MathFunction::Ceil => f64::ceil(value.into()),
                         MathFunction::Round => f64::round(value.into()),
+                        MathFunction::Cdf => {
+                            let normal = Normal::new(0.0, 1.0).expect("valid normal dist");
+                            normal.cdf(value.into())
+                        }
                         MathFunction::Exp => f64::exp(value.into()),
                         MathFunction::None => return Err(anyhow!("This should never happen!")),
                     };

src/token.rs

@@ -128,6 +128,8 @@ pub enum MathFunction {
     Round,
     /// e^x exponentiation
     Exp,
+    /// Standard Normal cumulative distribution function
+    Cdf,
     /// No function expected
     None,
 }
@@ -182,6 +184,7 @@ impl Token<'_> {
             "ceil" => Some(MathFunction::Ceil),
             "round" => Some(MathFunction::Round),
             "exp" => Some(MathFunction::Exp),
+            "cdf" => Some(MathFunction::Cdf),
             &_ => None,
         }
     }

tests/integration_tests.rs

@@ -147,6 +147,7 @@ fn test_expressions() {
     resolve_decimal!("round(3.6)", 4.0);
     resolve_decimal!("round(3.4)", 3.0);
     resolve_decimal!("exp(1)", std::f64::consts::E);
+    resolve_decimal!("cdf(0)", 0.5);
 
     resolve_err!("min()");
     resolve_err!("max()");