2016 2017 Ericsson AB, All Rights Reserved Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. The Initial Developer of the Original Code is Ericsson AB. Retired Myths Bjorn Gustavsson 2016-06-07 retired_myths.xml

We belive that the truth finally has caught with the following, retired myths.

Myth: Funs are Slow

Funs used to be very slow, slower than apply/3. Originally, funs were implemented using nothing more than compiler trickery, ordinary tuples, apply/3, and a great deal of ingenuity.

But that is history. Funs was given its own data type in R6B and was further optimized in R7B. Now the cost for a fun call falls roughly between the cost for a call to a local function and apply/3.

Myth: List Comprehensions are Slow

List comprehensions used to be implemented using funs, and in the old days funs were indeed slow.

Nowadays, the compiler rewrites list comprehensions into an ordinary recursive function. Using a tail-recursive function with a reverse at the end would be still faster. Or would it? That leads us to the myth that tail-recursive functions are faster than body-recursive functions.