Macrovich
Because any macros problem can be solved by another level of macros, Macrovich is a set of four macros to ease writing *.cljc
supporting Clojure, Clojurescript and self-hosted Clojurescript.
Excerpt from Being John Macrovich script:
- Girl Macrovich
- Macrovich Macrovich Macrovich Macrovich...
- (Macrovich looks confused. The Macrovich waiter approaches, pen and pad in hand, ready to take their orders.)
- Waiter Macrovich
- Macrovich Macrovich Macrovich?
- Girl Macrovich
- Macrovich Macrovich Macrovich Macrovich.
- Waiter Macrovich
- Macrovich Macrovich. (Turning to Macrovich) Macrovich?
Usage
Clojurescript >= 1.9.293 is required. This means Planck 2.0.0 or later is required. Lumo 1.0.0 is ok.
Add [net.cgrand/macrovich "0.2.1"]
to your dependencies.
Macrovich exposes four macros:
macros/deftime
andmacros/usetime
to clearly demarcate regions of code that should be run in the macro-definition stage or in the macro-usage stage. (In Clojure there's no distinction; in pure Clojurescript it's easy: just wrap the first stage in#?(:clj ...)
and the latter one in#?(:cljs ...)
; in self-hosted Clojurescript it's messy or everything gets evaluated twice; supporting the three at the same time is Macrovich's raison d'être.)macros/case
is a macro to use instead of reader conditionals in macros or macros-supporting fns. This solves a problem with regular Clojurescript where macros are Clojure code and thus are read by taking the:clj
branch of conditionals. Somacros/case
is like reader conditionals except the branch is picked at expansion time and not at definition time.macros/replace
is a macro to avoid repeating similar reader conditionals, see https://github.com/cgrand/xforms/blob/d4f0280bb50d8cc53c3a5dfe24b17fe7701b4e43/src/net/cgrand/xforms.cljc#L276 for an example.
Sample
Below is a sample being-john.cljc
file:
(ns being-john #?(:clj (:require [net.cgrand.macrovich :as macros]) :cljs (:require-macros [net.cgrand.macrovich :as macros] [net.cgrand.being :refer [add]]))) ; cljs must self refer macros (macros/deftime ; anything inside a deftime block will only appear at the macro compilation stage. (defmacro add [a b] `(+ ~a ~b))) (macros/usetime ; anything inside a usetime block will not appear at the macro compilation stage. (defn sum [a b] (add a b))) ; anything outside these block is always visible as usual
case
allows to select which form to emit in a macro based on the target language rather than the macro language. Consider these two macros:
(defmacro broken [] #?(:clj "clojure" :cljs "clojurescript")) (defmacro correct [] (macros/case :clj "clojure" :cljs "clojurescript")) ; or(defmacro correct [] `(macros/case :clj "clojure" :cljs "clojurescript")) ; this works too, so no need to unquote in the middle of a syntax quotation and mess with gensyms
In regular (Clojure-hosted) Clojurescript (broken)
expands to "clojure"
while (correct)
expands to "clojurescript"
.
Example
The xforms lib has been converted to cljc:
- https://github.com/cgrand/xforms/blob/cljc/src/net/cgrand/xforms.cljc
- https://github.com/cgrand/xforms/blob/cljc/src/net/cgrand/xforms/rfs.cljc
- https://github.com/cgrand/xforms/blob/cljc/test/net/cgrand/xforms_test.clj
License
Copyright © 2016-2017 Christophe Grand
Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.