menu_book Course Curriculum (Prolog) expand_more
if then else
Learn if then else in Prolog through a focused explanation, a dedicated construct-specific example, an engineering boundary, and a mastery check.
if then else is an atomic Prolog topic inside Recursion & Search. This lesson focuses on how the if then else construct is written, what it changes, and when it is the right tool.
Trace the example line by line. Identify the exact syntax for if then else, 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
label(N,L) :- (N>=0 -> L=nonnegative ; L=negative).For if then else, 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.