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head tail pattern
Learn head tail pattern in Prolog through a focused explanation, a dedicated construct-specific example, an engineering boundary, and a mastery check.
head tail pattern is an atomic Prolog topic inside Lists. This lesson focuses on how the head tail pattern construct is written, what it changes, and when it is the right tool.
Trace the example line by line. Identify the exact syntax for head tail pattern, the input state before it runs, and the resulting value, control flow, database state, hardware behavior, or runtime effect afterward. Neighboring lessons use different constructs rather than renamed copies of this one.
Topic-specific example
first([H|_], H).
rest([_|T], T).For head tail pattern, test the boundary that belongs to this exact feature rather than a generic failure case. Check invalid or empty input, NULL/unknown state, numeric limits, transaction or exception behavior, synthesis/runtime constraints, ownership/permission rules, or backtracking/control-flow effects where they apply.