fn_transformer_ops_demo/
fn_transformer_ops_demo.rs

1/*******************************************************************************
2 *
3 *    Copyright (c) 2025 - 2026 Haixing Hu.
4 *
5 *    SPDX-License-Identifier: Apache-2.0
6 *
7 *    Licensed under the Apache License, Version 2.0.
8 *
9 ******************************************************************************/
10//! Demonstrates the usage of FnTransformerOps extension trait
11//!
12//! This example shows how to directly use and_then, compose, and when methods on closures,
13//! without explicitly wrapping them in BoxTransformer, RcTransformer, or ArcTransformer.
14
15use qubit_function::{
16    FnTransformerOps,
17    Transformer,
18};
19
20fn main() {
21    println!("=== FnTransformerOps Example ===\n");
22
23    // 1. Basic and_then composition
24    println!("1. Basic and_then composition:");
25    let double = |x: i32| x * 2;
26    let to_string = |x: i32| x.to_string();
27    let composed = double.and_then(to_string);
28    println!(
29        "   double.and_then(to_string).apply(21) = {}",
30        composed.apply(21)
31    );
32    println!();
33
34    // 2. Chained and_then composition
35    println!("2. Chained and_then composition:");
36    let add_one = |x: i32| x + 1;
37    let double = |x: i32| x * 2;
38    let to_string = |x: i32| x.to_string();
39    let chained = add_one.and_then(double).and_then(to_string);
40    println!(
41        "   add_one.and_then(double).and_then(to_string).apply(5) = {}",
42        chained.apply(5)
43    ); // (5 + 1) * 2 = 12
44    println!();
45
46    // 3. compose reverse composition
47    println!("3. compose reverse composition:");
48    let double = |x: i32| x * 2;
49    let add_one = |x: i32| x + 1;
50    let composed = double.compose(add_one);
51    println!(
52        "   double.compose(add_one).apply(5) = {}",
53        composed.apply(5)
54    ); // (5 + 1) * 2 = 12
55    println!();
56
57    // 4. Conditional transformation when
58    println!("4. Conditional transformation when:");
59    let double = |x: i32| x * 2;
60    let conditional = double.when(|x: &i32| *x > 0).or_else(|x: i32| -x);
61    println!("   double.when(x > 0).or_else(negate):");
62    println!("     transform(5) = {}", conditional.apply(5)); // 10
63    println!("     transform(-5) = {}", conditional.apply(-5)); // 5
64    println!();
65
66    // 5. Complex composition
67    println!("5. Complex composition:");
68    let add_one = |x: i32| x + 1;
69    let double = |x: i32| x * 2;
70    let triple = |x: i32| x * 3;
71    let to_string = |x: i32| x.to_string();
72
73    let complex = add_one
74        .and_then(double.when(|x: &i32| *x > 5).or_else(triple))
75        .and_then(to_string);
76
77    println!("   add_one.and_then(double.when(x > 5).or_else(triple)).and_then(to_string):");
78    println!("     transform(1) = {}", complex.apply(1)); // (1 + 1) = 2 <= 5, so 2 * 3 = 6
79    println!("     transform(5) = {}", complex.apply(5)); // (5 + 1) = 6 > 5, so 6 * 2 = 12
80    println!("     transform(10) = {}", complex.apply(10)); // (10 + 1) = 11 > 5, so 11 * 2 = 22
81    println!();
82
83    // 6. Type conversion
84    println!("6. Type conversion:");
85    let to_string = |x: i32| x.to_string();
86    let get_length = |s: String| s.len();
87    let length_transformer = to_string.and_then(get_length);
88    println!(
89        "   to_string.and_then(get_length).apply(12345) = {}",
90        length_transformer.apply(12345)
91    ); // 5
92    println!();
93
94    // 7. Closures that capture environment
95    println!("7. Closures that capture environment:");
96    let multiplier = 3;
97    let multiply = move |x: i32| x * multiplier;
98    let add_ten = |x: i32| x + 10;
99    let with_capture = multiply.and_then(add_ten);
100    println!(
101        "   multiply(3).and_then(add_ten).apply(5) = {}",
102        with_capture.apply(5)
103    ); // 5 * 3 + 10 = 25
104    println!();
105
106    // 8. Function pointers
107    println!("8. Function pointers:");
108    fn double_fn(x: i32) -> i32 {
109        x * 2
110    }
111    fn add_one_fn(x: i32) -> i32 {
112        x + 1
113    }
114    let fn_composed = double_fn.and_then(add_one_fn);
115    println!(
116        "   double_fn.and_then(add_one_fn).apply(5) = {}",
117        fn_composed.apply(5)
118    ); // 5 * 2 + 1 = 11
119    println!();
120
121    // 9. Multi-conditional transformation
122    println!("9. Multi-conditional transformation:");
123    let abs = |x: i32| x.abs();
124    let double = |x: i32| x * 2;
125    let transformer = abs.when(|x: &i32| *x < 0).or_else(double);
126    println!("   abs.when(x < 0).or_else(double):");
127    println!("     transform(-5) = {}", transformer.apply(-5)); // abs(-5) = 5
128    println!("     transform(5) = {}", transformer.apply(5)); // 5 * 2 = 10
129    println!("     transform(0) = {}", transformer.apply(0)); // 0 * 2 = 0
130    println!();
131
132    println!("=== Example completed ===");
133}
fn_transformer_ops_demo/fn_transformer_ops_demo.rs

fn_transformer_ops_demo/
fn_transformer_ops_demo.rs
