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Made title more descriptive of actual question. Minor clean-up

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edited Jul 27, 2014 at 12:54

How does patterns work in Which function definitions, when they overlapdefinition is used to evaluate an expression that matches the lefthand side of more than one definition?

In a case like this:

f[a_] :=a;= a;
f[{a_, b_}] :=a;= a;

I'm wondering whether I should expect f[{2, 3}] to return {2,3} or 2, because:

MatchQ[{2, 3}, a_] == MatchQ[{2, 3}, {a_, b_}]

Is the behaviour in this situation defined, or should I avoid this at all costs?

In a case like this:

f[a_]:=a;
f[{a_,b_}]:=a;

I'm wondering whether I should expect f[{2, 3}] to return {2,3} or 2, because:

MatchQ[{2, 3}, a_] == MatchQ[{2, 3}, {a_, b_}]

Is the behaviour in this situation defined, or should I avoid this at all costs?

In a case like this:

f[a_] := a;
f[{a_, b_}] := a;

I'm wondering whether I should expect f[{2, 3}] to return {2,3} or 2, because:

MatchQ[{2, 3}, a_] == MatchQ[{2, 3}, {a_, b_}]

Is the behaviour in this situation defined, or should I avoid this at all costs?

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asked Jul 27, 2014 at 12:07

In a case like this:

f[a_]:=a;
f[{a_,b_}]:=a;

I'm wondering whether I should expect f[{2, 3}] to return {2,3} or 2, because:

MatchQ[{2, 3}, a_] == MatchQ[{2, 3}, {a_, b_}]

Is the behaviour in this situation defined, or should I avoid this at all costs?

argument-patterns