fp_library/types/
string.rs

1//! Implementations for [`String`].
2//!
3//! This module provides implementations of functional programming traits for the standard library [`String`] type.
4
5use crate::{
6	classes::{monoid::Monoid, semigroup::Semigroup},
7	impl_kind,
8	kinds::*,
9};
10
11impl_kind! {
12	for String {
13		type Of<'a> = String;
14	}
15}
16
17impl Semigroup for String {
18	/// The result of combining two strings.
19	///
20	/// This method combines two strings into a single string.
21	///
22	/// ### Type Signature
23	///
24	/// `forall. Semigroup String => (String, String) -> String`
25	///
26	/// ### Parameters
27	///
28	/// * `a`: The first string.
29	/// * `b`: The second string.
30	///
31	/// ### Returns
32	///
33	/// The combined string.
34	///
35	/// ### Examples
36	///
37	/// ```
38	/// use fp_library::classes::semigroup::Semigroup;
39	///
40	/// let s1 = "Hello, ".to_string();
41	/// let s2 = "World!".to_string();
42	/// let result = String::append(s1, s2);
43	/// assert_eq!(result, "Hello, World!");
44	///
45	/// // Using the free function
46	/// use fp_library::classes::semigroup::append;
47	/// assert_eq!(append("foo".to_string(), "bar".to_string()), "foobar");
48	/// ```
49	fn append(
50		a: Self,
51		b: Self,
52	) -> Self {
53		a + &b
54	}
55}
56
57impl Monoid for String {
58	/// The identity element.
59	///
60	/// This method returns the identity element of the monoid.
61	///
62	/// ### Type Signature
63	///
64	/// `forall. Monoid String => () -> String`
65	///
66	/// ### Returns
67	///
68	/// The identity element.
69	///
70	/// ### Examples
71	///
72	/// ```
73	/// use fp_library::classes::monoid::Monoid;
74	///
75	/// let empty_string = String::empty();
76	/// assert_eq!(empty_string, "");
77	///
78	/// // Using the free function
79	/// use fp_library::classes::monoid::empty;
80	/// assert_eq!(empty::<String>(), "");
81	/// ```
82	fn empty() -> Self {
83		String::new()
84	}
85}
86
87#[cfg(test)]
88mod tests {
89	use crate::classes::{monoid::Monoid, semigroup::append};
90	use quickcheck_macros::quickcheck;
91
92	// Semigroup Laws
93
94	/// Tests the associativity law for Semigroup.
95	#[quickcheck]
96	fn semigroup_associativity(
97		a: String,
98		b: String,
99		c: String,
100	) -> bool {
101		append(a.clone(), append(b.clone(), c.clone())) == append(append(a, b), c)
102	}
103
104	// Monoid Laws
105
106	/// Tests the left identity law for Monoid.
107	#[quickcheck]
108	fn monoid_left_identity(a: String) -> bool {
109		append(String::empty(), a.clone()) == a
110	}
111
112	/// Tests the right identity law for Monoid.
113	#[quickcheck]
114	fn monoid_right_identity(a: String) -> bool {
115		append(a.clone(), String::empty()) == a
116	}
117}
fp_library/types/string.rs

fp_library/types/
string.rs
