xlet

Let binding using Scala-like pattern extraction.

Usage

The xlet macro creates a lexical context by first matching a binding pattern against an expression and then binding the symbols in the pattern to values extracted from the expression similar to the pattern extraction mechanism in Scala.

The symbol _ is used as a wildcard that is not bound. It is used to ignore the corresponding value in the extraction.

The expression used for extraction must evaluate to a type that extends the protocol IExtractPattern.

Example:

(extend-type java.net.URL
        atollier.xlet/IExtractPattern
        (unapply [in]
          [(.getProtocol in) (.getHost in) (.getPort in) (.getPath in)]))

(atollier.xlet/xlet (java.net.URL. "http://www.google.com/")
        ["https" host _ _] (str "HTTPS " host)
        ["http"  host _ _] (str "HTTP " host))

(extend-type java.util.Date
    atollier.xlet/IExtractPattern
    (unapply [in]
        [(.getYear in) (.getMonth in) (.getDate in)]))

(atollier.xlet/xlet (java.util.Date. 2016 2 6)
    [_ _ _ d] (throw (Exception. "Won't be thrown."))
    [_ _ d] (str "Day of month: " d))

License

Copyright © 2016 Shiyas Rasheed

Distributed under the Eclipse Public License either version 1.0.