mercury — consolidated language guide — DedSec Project

Mercury

Typical use: Logic programming.

Suggested file extension: .m.

How to run / environment: mmc --make hello (Mercury toolchain).

Starter example

:- module hello.
:- interface.
:- import_module io.
:- pred main(io::di, io::uo) is det.
:- implementation.
main(!IO) :- io.write_string("Hello, Ada!\n", !IO).

How to read it

Logic language with strict type and mode declarations.

Common pitfall

Logic language with strict type and mode declarations.

Mercury — Expanded practice workbook

Inspect the smallest source

:- module hello.
:- interface.
:- import_module io.
:- pred main(io::di, io::uo) is det.
:- implementation.
main(!IO) :- io.write_string("Hello, Ada!\n", !IO).

Run or compilation context: mmc --make hello (Mercury toolchain).. Treat this as a baseline: save a copy, confirm the toolchain version and note whether the example merely evaluates a value, prints text, or creates external effects. Production accounts, datasets and hardware must not be used for first attempts.

Work through the actual mechanism

Create a deterministic predicate and a multi-solution predicate over a small relation. Declare modes and determinism, and let the compiler reject a mismatched declaration.

Diagnose the sharp edge

Mercury treats determinism and instantiation states as part of its interface; Prolog syntax is similar but not freely interchangeable.

Mercury — Focused mastery pathway

Applied exercises

1. Describe a tiny parent/ancestor relation and query it in the proper language host.
2. Show how an additional fact changes the result set.
3. Explain termination or search-order effects of a recursive rule.

• Does execution search for solutions or execute steps in order?
• Which exact runtime, compiler, host, and version does the reference need?
• What is the smallest working program and what side effects does it have?
• How do syntax, logic, and environment errors differ?
• How can invalid inputs be tested without modifying real user files?