4mitch

Rich Already Answered That!

A list of commonly asked questions, design decisions, reasons why Clojure is the way it is as they were answered directly by Rich (even when from many years ago, those answers are pretty much valid today!). Feel free to point friends and colleagues here next time they ask (again). Answers are pasted verbatim (I've made small adjustments for readibility, but never changed a sentence) from mailing lists, articles, chats. The link below jumps at the answer in this file, the link on the question points back at the original post.

Index:

• Why no pattern matching?
• Why no tail call optimization?
• Why you don't accept pull requests?

4mitch

Clojure Destructuring Tutorial and Cheat Sheet

(Related blog post)

Simply put, destructuring in Clojure is a way extract values from a datastructure and bind them to symbols, without having to explicitly traverse the datstructure. It allows for elegant and concise Clojure code.

Vectors

4mitch

function sum (fn, xs) {
  var toRet = 0;
  for (var i = 0, ii = xs.length; i < ii; i++) {
    toRet += fn(xs[i], i, xs);
  }
  return toRet;
}

function update(t, o) {
  for (var k in o) {

4mitch

(let [a [1 1 2 3 4]
      b [1 2 3 4 1]]
 (and     
    #_(time
     (and 
      (.containsAll a b) 
      (.containsAll b a)))

    (time
      (=  (frequencies a)

4mitch

Docker

Shortcuts

$ curl -fsSL https://raw.github.com/tcnksm/docker-alias/master/zshrc >> ~/.bashrc && source ~/.bashrc

# ------------------------------------

4mitch

Howto: Install Alpine Linux 3.3 on VirtualBox OSX

• Latest Standard ISO version x86_64 is recommended (http://alpinelinux.org/downloads/)
• Create new VM ("Linux 2.6 / 3.x / 4.x (64-bit)")
• 1 CPU w/ 512BM RAM and 1 GB default (VDI) disk is more than sufficient
• Default networking (NAT)
• Boot and add Alpine ISO as attached virtual install media
• Default root password is blank (though note - ssh PermitRootLogin defaults to disallow blank passwords and: prohibit-password; switch to yes for Host ssh)
• Run setup-alpine
• Defaults are fine, but you do want "sys" disk setup to sda, y to confirm

4mitch

function Convert-ByFilter($values, $predicate) {
    return $values | where { & $predicate $_ }
}

Describe "Higher Order Functions" {
    $values = @(1, 2, 3, 4)
 
    It "Should filter even" {
        $evenPredicate = { param($value) return $value % 2 -eq 0 }
        $even = Convert-ByFilter $values $evenPredicate

4mitch

XPath                       ::= Expr
ParamList                   ::= Param ("," Param)*
Param                       ::= "$" EQName TypeDeclaration?
FunctionBody                ::= EnclosedExpr
EnclosedExpr                ::= "{" Expr "}"
Expr                        ::= ExprSingle ("," ExprSingle)*
ExprSingle                  ::= ForExpr
                              | LetExpr
                              | QuantifiedExpr
                              | IfExpr

4mitch

XPath                       ::= Expr
ParamList                   ::= Param ("," Param)*
Param                       ::= "$" EQName TypeDeclaration?
FunctionBody                ::= EnclosedExpr
EnclosedExpr                ::= "{" Expr "}"
Expr                        ::= ExprSingle ("," ExprSingle)*
ExprSingle                  ::= ForExpr
                              | LetExpr
                              | QuantifiedExpr
                              | IfExpr

4mitch

=> (clojure.core.server/start-server {:name "debug connection" :port 5555 :accept 'clojure.core.server/repl})
#object[java.net.ServerSocket 0x631883f0 "ServerSocket[addr=localhost/127.0.0.1,localport=5555]"]