Introduction
Threading macros (or arrow macros) are used in Clojure for compose many function calls.
Other language like Elixir, LiveScript or F# use a pipe operator |> for the same functionality.
In Haxe we can create the same utility with a simple macro. Thanks to the static analyzer we can eliminate the temp variables used for memorize the intermediate values.
The code macro
import haxe.macro.Expr; import haxe.macro.Context; using haxe.macro.ExprTools; using haxe.macro.MacroStringTools; class FunctionThread { public static macro function thread(exprs:Array<Expr>) { var exprs = [ for (expr in exprs) macro var _ = $expr ]; exprs.push(macro _); return macro $b{exprs}; } }
A simple example
import FunctionThread.thread; class Main { static function sum(a, b) return a + b; static function main() { var x = 0; var res = thread( sum(x,1), sum(_,1), sum(_,2), sum(3,_) ); trace(res); } }
The code generated in JavaScript without the static analyzer
// Generated by Haxe 3.3.0 (function () { "use strict"; var HxOverrides = function() { }; HxOverrides.iter = function(a) { return { cur : 0, arr : a, hasNext : function() { return this.cur < this.arr.length; }, next : function() { return this.arr[this.cur++]; }}; }; var Main = function() { }; Main.sum = function(a,b,c) { if(c == null) { c = 0; } return a + b + c; }; Main.main = function() { var x = 0; var _ = Main.sum(x,1); var _1 = Main.sum(_,1,5); var _2 = Main.sum(_1,2); var _3 = Main.sum(3,_2,7); var res = _3; console.log(res); }; Main.main(); })();
The code generated with the static analyzer
In this case thanks to the static analyzer we don't need of the temp variables
// Generated by Haxe 3.3.0 (function () { "use strict"; var HxOverrides = function() { }; HxOverrides.iter = function(a) { return { cur : 0, arr : a, hasNext : function() { return this.cur < this.arr.length; }, next : function() { return this.arr[this.cur++]; }}; }; var Main = function() { }; Main.sum = function(a,b) { return a + b; }; Main.main = function() { console.log(Main.sum(3,Main.sum(Main.sum(Main.sum(0,1),1),2))); }; Main.main(); })();
With inline function
With inline of sum and static analyzer the output is:
console.log(7);
