f @@ {a,b,c,...} == f[a,b,c,...]

f @@ g[a,b] == f[a,b]

f[Sequence[a,b]] == f[a,b]

f[ Sequence @@ {a,b}] == f[a,b]

Apply[f, {{a,b},{c,d}}, {1}] == {f[a,b], f[c,d]}

f[l_List]:=l[[1]]^2+l[[2]]^2

g[l_List] := l.l

h[l_List]:= Norm[l]^2

Print[{f[{a, b}], g[{a, b}], h[{a, b}]}]

{a^2 + b^2, a^2 + b^2, Abs[a]^2 + Abs[b]^2}

i[l_List] := Total@Table[j^2, {j, l}]

j[l_List] := SquaredEuclideanDistance[l, ConstantArray[0, Length[l]]

f[{__}] = a ^ 2 + b ^ 2;

s[l_List] = Total[l]

s[l_List] := Total[l]

f[{a_,b_}]:= a^2+b^2;