lambdaplusplus

A small, header-only C++20 library of functional utilities (compose, attempt, match).

Usage

#include <lambda.h>

#include <iostream>
#include <string>

int main() {
    auto add_one   = [](int x) { return x + 1; };
    auto times_two = [](int x) { return x * 2; };
    auto f = lambda::compose(add_one, times_two);  // add_one(times_two(x))
    std::cout << f(3) << '\n';                      // -> 7

    // attempt runs a callable and swallows exceptions: optional<R> for
    // value-returning callables (nullopt on throw), bool for void callables.
    auto parsed = lambda::attempt([](const std::string& s) { return std::stoi(s); }, "41");
    std::cout << parsed.value_or(-1) << '\n';       // -> 41
}

The public API — all in <lambda.h>, namespace lambda:

Function	Description
compose(f, g)	Returns a callable computing f(g(args...)).
attempt(f, args...)	Invokes f(args...), swallowing exceptions — std::optional<R>, or bool when f returns void.
nothrow(f)	Wraps f into a reusable non-throwing callable; nothrow(f)(args...) behaves like attempt(f, args...).
match(x, cases...)	Invokes the first case whose parameter type matches x exactly — no implicit conversions, selected at compile time via if constexpr. Put a generic [](auto&&){…} last as the catch-all (_).

Consuming from another CMake project

After installing (cmake --install build):

find_package(lambdaplusplus REQUIRED)
target_link_libraries(my_app PRIVATE lambdaplusplus::lambdaplusplus)

Or vendor it directly as a subdirectory:

add_subdirectory(external/lambdaplusplus)
target_link_libraries(my_app PRIVATE lambdaplusplus::lambdaplusplus)

License

MIT © 2026 David Clevenger