<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><br></div><div>To begin with, your example won't compile, but the question is still valid.</div><div><br></div><div>Consider this program:</div><div><br></div><div>=================</div><div><div>-module(foldtest).</div><div>-export([f1/2, f2/2]).</div><div><br></div><div>f1(Acc, Lst) -></div><div> F = fun(A,B) -> my_function(A,B) end,</div><div> lists:foldl(F, Acc, Lst).</div><div><br></div><div>f2(Acc, Lst) -></div><div> lists:foldl(fun my_function/2, Acc, Lst).</div><div><br></div><div>my_function(X, Acc) -></div><div> [X|Acc].</div></div><div><div>=================</div><div></div></div><div><br></div><div>I believe this illustrates the question, but compiles and runs correctly.</div><div><br></div><div><div>Eshell V5.9 (abort with ^G)</div><div>1> foldtest:f1([], [1,2,3]).</div><div>[3,2,1]</div><div>2> foldtest:f2([], [1,2,3]).</div><div>[3,2,1]</div></div><div><br></div><div>Now, let's compile the code with `erlc -S foldtest.erl` (generating ASM code):</div><div><br></div><div><div>{function, f1, 2, 2}.</div><div> {label,1}.</div><div> {line,[{location,"foldtest.erl",4}]}.</div><div> {func_info,{atom,foldtest},{atom,f1},2}.</div><div> {label,2}.</div><div> {allocate,2,2}.</div><div> {move,{x,1},{y,0}}.</div><div> {move,{x,0},{y,1}}.</div><div> {make_fun2,{f,14},0,0,0}.</div><div> {move,{y,0},{x,2}}.</div><div> {move,{y,1},{x,1}}.</div><div> {line,[{location,"foldtest.erl",6}]}.</div><div> {call_ext_last,3,{extfunc,lists,foldl,3},2}.</div><div><br></div><div><br></div><div>{function, f2, 2, 4}.</div><div> {label,3}.</div><div> {line,[{location,"foldtest.erl",9}]}.</div><div> {func_info,{atom,foldtest},{atom,f2},2}.</div><div> {label,4}.</div><div> {allocate,2,2}.</div><div> {move,{x,1},{y,0}}.</div><div> {move,{x,0},{y,1}}.</div><div> {make_fun2,{f,12},0,0,0}.</div><div> {move,{y,0},{x,2}}.</div><div> {move,{y,1},{x,1}}.</div><div> {line,[{location,"foldtest.erl",10}]}.</div><div> {call_ext_last,3,{extfunc,lists,foldl,3},2}.</div></div><div><br></div><div>As you can tell, the two alternatives generate identical code.</div><div><br></div><div>The fun is compiled into a regular function, albeit with a funny name, and calling it carries the same cost as calling a hand-written function. Actually instantiating a fun context carries a slight overhead depending on the number of variables that need to be imported into the context (in this case, zero). There will be one level of indirection in both cases.</div><div><br></div><div>BR,</div><div>Ulf W</div><br><div><div>On 23 Sep 2012, at 02:07, James Rosenblum wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div style="color: rgb(0, 0, 0); font-size: 19px; font-family: arial, helvetica, sans-serif; background-color: transparent; font-style: normal; ">Is there an appreciable difference in these two ways of passing a function?</div><div style="color: rgb(0, 0, 0); font-size: 19px; font-family: arial, helvetica, sans-serif; background-color: transparent; font-style: normal; "><br></div><div style="color: rgb(0, 0, 0); font-size: 19px; font-family: arial, helvetica, sans-serif; background-color: transparent; font-style: normal; ">F = fun(A,B) -> my_function(A,B) end.</div><div style="color: rgb(0, 0, 0); font-size: 19px; font-family: arial, helvetica, sans-serif; background-color: transparent; font-style: normal; ">lists:map(F, Lst)</div><div style="color: rgb(0, 0, 0); font-size: 19px; font-family: arial, helvetica, sans-serif; background-color: transparent; font-style: normal; "><br></div><div style="color: rgb(0, 0, 0); font-size: 19px; font-family: arial, helvetica, sans-serif; background-color: transparent; font-style: normal; ">vs.</div><div style="color: rgb(0, 0, 0); font-size: 19px; font-family: arial, helvetica, sans-serif; background-color: transparent; font-style: normal; "><br></div><div style="color: rgb(0, 0, 0); font-size: 19px; font-family: arial, helvetica, sans-serif; background-color: transparent; font-style: normal; ">-export([my_function/2]).</div><div style="color: rgb(0, 0, 0); font-size: 19px; font-family: arial, helvetica, sans-serif; background-color: transparent; font-style: normal; "><br></div><div style="color: rgb(0, 0, 0); font-size: 19px; font-family: arial, helvetica, sans-serif; background-color: transparent; font-style: normal; ">lists:map(fun my_function/2, Lst)</div></blockquote></div><br><div apple-content-edited="true">
<div><div>Ulf Wiger, Co-founder & Developer Advocate, Feuerlabs Inc.</div><div><a href="http://feuerlabs.com">http://feuerlabs.com</a></div></div><div><br></div><br class="Apple-interchange-newline">
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