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Prolog / Control & Meta

forall

Learn forall in Prolog through a focused explanation, a dedicated construct-specific example, an engineering boundary, and a mastery check.

10 min read • Intermediate

forall is an atomic Prolog topic inside Control & Meta. This lesson focuses on how the forall construct is written, what it changes, and when it is the right tool.

Trace the example line by line. Identify the exact syntax for forall, 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

prolog-05-05-forall.pl
prolog Try It Live 
all_positive(L) :- forall(member(X,L), X>0).
Edge case / engineering note

For forall, 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.

Content source & attribution
Original Syntaxis Content · Original Syntaxis Content

Lesson quizzes

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