iopq · September 7, 2016 21:02 · Sep 7, 2016
diff --git a/lib.rs b/lib.rs
@@ -0,0 +1,83 @@
+//! The `fizzbuzz` crate provides the way to get a customizable fizzbuzz implementation
+//! 
+//! # Examples
+//! 
+//! ```
+//!    let mut acc = "".to_string();
+//!    for i in 1..16 {
+//!        acc = acc + &*fizzbuzz::cowbuzz(&[
+//!            ("Fizz", &|i: i32| i % 3 == 0),
+//!            ("Buzz", &|i: i32| i % 5 == 0),
+//!        ], i) + " ";
+//!    }
+//! 
+//!    assert_eq!(acc, "1 2 Fizz 4 Buzz Fizz 7 8 Fizz Buzz 11 Fizz 13 14 FizzBuzz ".to_string());
+//! ```
+
+extern crate monoid;
+use monoid::Monoid;
+use std::borrow::Cow;
+use std::convert::Into;
+
+///takes a tuple of strings and conditions
+///shows the numbers if conditions are false
+pub fn fizzbuzz<'a>(tuples: &[(&'a str, &Fn(i32) -> bool)], i: i32) -> String {
+    let default = || i.to_string();
+    accumulate(tuples, i).unwrap_or_else(default)
+    //unwrap_or_else is equivalent to fromMaybe
+}
+
+///takes a tuple of strings and conditions
+///shows the numbers if conditions are false
+///faster than using a String
+pub fn cowbuzz<'a>(tuples: &[(&'a str, &Fn(i32) -> bool)], i: i32) -> Cow<'a, str> {
+    let default = || i.to_string().into();
+    accumulate(tuples, i).unwrap_or_else(default)
+    //unwrap_or_else is equivalent to fromMaybe
+}
+
+//does the monoid operation on the slice of tuples if the closure evaluates to true
+fn accumulate<'a, T: Monoid>(tuples: &[(&'a str, &Fn(i32) -> bool)], i: i32) -> Option<T> 
+        where &'a str: Into<T> {
+
+	tuples.iter()
+		.filter(|&(_,include_fn)| include_fn(i))
+		.map(|(concat_str,_)| concat_str)
+		.fold(None, |acc, concat_str| acc.op(concat_str));
+}
+
+//concatenates the strings if the condition is met
+fn append<'a, T: Monoid>(a: Option<T>, b: &'a str, include: bool) -> Option<T>
+        where &'a str: Into<T> {
+    a.op( if_some(b, include) )
+}
+
+//only perform an expensive operation if the condition is true
+fn if_some<T: Into<U>, U>(a: T, cond: bool) -> Option<U> {
+    if cond { Some(a.into()) } else { None }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::append;
+
+    #[test]
+    fn none() {
+        assert_eq!(None::<String>, append(None, "b", false));
+    }
+
+    #[test]
+    fn a() {
+        assert_eq!(Some("a".to_string()), append(Some("a".to_string()), "b", false));
+    }
+
+    #[test]
+    fn b() {
+        assert_eq!(Some("b".to_string()), append(None, "b", true));
+    }
+
+    #[test]
+    fn ab() {
+        assert_eq!(Some("ab".to_string()), append(Some("a".to_string()), "b", true));
+    }
+}
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