cpp

LangForge C++ Examples

The C++ examples are generated-on-demand projects. Each example keeps the grammar in .lf, handwritten semantics in normal C++ source, and generated scanner/parser output under an ignored generated/ directory.

Run one example:

make -C examples/cpp/calc run
make -C examples/cpp/datakeeper run
make -C examples/cpp/draw run
make -C examples/cpp/vehicle-report run

Run generated-code checks:

make -C examples/cpp/calc test
make -C examples/cpp/datakeeper test
make -C examples/cpp/draw test
make -C examples/cpp/vehicle-report test

The Makefiles invoke LangForge from source by default:

LANG_FORGE ?= $(GO) run ../../../cmd/lang-forge

After installing or building a standalone lang-forge binary, override that variable instead:

make -C examples/cpp/calc LANG_FORGE=lang-forge run

Generated C++ output uses conventional filenames: tokens.hpp, scanner.hpp, scanner.cpp, parser.hpp, parser_typed.hpp, and parser.cpp. Handwritten code includes generated headers through paths such as generated/parser.hpp so IDEs can see generated types while the generated directory remains the single source of generated declarations.

The examples default to generated typed reducer adapters and keep --boxed as an explicit compatibility mode. The typed path validates named RHS labels and ReducerMap coverage before delegating to the boxed reducer implementation. When a spec declares structural semantic values as std::nullptr_t, reducers return nullptr rather than {} when using typed adapters or direct typed handlers. Boxed-only reducers can tolerate an empty std::any only when that value is never read, but nullptr keeps the result consistent with the declared no-op type.

C++ examples prefer source-based parsing by passing a generated Scanner to parse_value(scanner, reducers) or parse_recovering(scanner). Token vectors remain available for tests and token inspection. Reusable handwritten code should hide generated headers behind parser facades, use direct typed reducers where practical, keep std::any_cast at compatibility boundaries, and express ownership with std::unique_ptr, std::variant, or a domain result type instead of exposing generated parser stack values.

The DRAW C++ example writes a PNG image with a tiny local encoder rather than using an external image library.

The Makefiles include shared fragments from examples/mk and default to shared valid fixtures under examples/testdata. For a smaller copyable starter project, use examples/templates/cpp/mini-compiler.

For a modern C++ starter with public headers under include/, generated output isolated under generated/, a domain-level parser facade, direct typed reducer handlers, intentional std::unique_ptr/std::variant ownership, and CMake integration, use examples/templates/cpp/layered-compiler.

For the recommended handwritten C++ reducer map, parser facade, semantic policy/interface, reusable library, and multi-parser shapes, read Handwritten Integration Guide.