Pattern Matching - Prolog vs. Haskell

Question

This is not a homework question, rather an exam study guide question. What is the difference between pattern matching in Prolog Vs Haskell?

I\'ve done some research and

Answer 1

Nobody mentioned the following very important difference. Pattern matching in Prolog is tried for every clause of a predicate, even if one of the previous matches has succeeded (unless stopped short by a cut). But in Haskell pattern matching on clauses is attempted only until the first success. No other alternatives are tried (unless the match was rejected by a guard).

Prolog's pattern matching establishes an equality constraint in most general sense (see answer by @false for details). Sharing is explicit: A=B, A=5 sets B=5 as well. This is possible because Prolog's logvar can be in not-yet-set (i.e. uninstantiated) state. This makes tying-a-knot easy (a basic programming technique actually, viz. difference lists).

In Haskell, any variable is allowed to be defined only once at the syntax level. In Prolog a logvar is set only once too (sans backtracking), but it is allowed to point at an incomplete structure (data), where holes are represented by other not-yet-instantiated logvars which can be set at any later point in time.

In Haskell, a given structure defined with guarded recursion is progressively fleshed out as demanded by access. In Prolog, after the initial instantiation of a variable, any subsequent unification is turned into verification of terms' compatibility and possible further (perhaps partial yet again) instantiation ("filling up" the holes explicitly).