Clojure Core

Namespaces

clojure
- core
  - protocols
- inspector
- java
  - browse
  - io
  - javadoc
  - shell
- main
- pprint
- repl
- set
- stacktrace
- string
- template
- test
  - junit
  - tap
- walk
- xml
- zip

You're viewing version 1.2.0 of letfn. The latest stable version of Clojure Core is 1.3.0.

1.2.0

1.2.0
1.3.0

letfn

Takes a vector of function specs and a body, and generates a set of
bindings of functions to their names. All of the names are available
in all of the definitions of the functions, as well as the body.

fnspec ==> (fname [params*] exprs) or (fname ([params*] exprs)+)

1 Example top

link | changes
```
user=> (letfn [(twice [x]
                 (* x 2))
               (six-times [y]
                 (* (twice y) 3))]
         (println "Twice 15 =" (twice 15))
         (println "Six times 15 =" (six-times 15)))
Twice 15 = 30
Six times 15 = 90
nil

;; Unable to resolve symbol: twice in this context
user=> (twice 4)
; Evaluation aborted.

;; Unable to resolve symbol: six-times in this context
user=> (six-times 100)
; Evaluation aborted.
```
user=> (letfn [(twice [x] (* x 2)) (six-times [y] (* (twice y) 3))] (println "Twice 15 =" (twice 15)) (println "Six times 15 =" (six-times 15))) Twice 15 = 30 Six times 15 = 90 nil ;; Unable to resolve symbol: twice in this context user=> (twice 4) ; Evaluation aborted. ;; Unable to resolve symbol: six-times in this context user=> (six-times 100) ; Evaluation aborted.

Source clojure/core.clj:5246 top

(defmacro letfn 
  "Takes a vector of function specs and a body, and generates a set of
  bindings of functions to their names. All of the names are available
  in all of the definitions of the functions, as well as the body.

  fnspec ==> (fname [params*] exprs) or (fname ([params*] exprs)+)"
  {:added "1.0"}
  [fnspecs & body] 
  `(letfn* ~(vec (interleave (map first fnspecs) 
                             (map #(cons `fn %) fnspecs)))
           ~@body))

Vars in clojure.core/letfn: cons defmacro first interleave map vec concat fn list seq

Used in 14 other vars keep-indexed map-indexed state-m-until with-io-streams select choose discrete flatten-nodes-coll zip-select-fragments* zip-select-nodes* who-specializes who-calls inspector-content inspect-in-emacs

Comments top

1 comment(s) for letfn.

Justinus

link

Using letfn allows you to create local functions that reference each other whereas (let myfunc #(...)]...) wouldn't because it executes its bindings serially.

ClojureDocs(beta)