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Q. How do I invoke LeMP programmatically?

A. There are two ways. Either you can use MacroProcessor directly, or you can use Compiler (see Compiler.cs), which is a wrapper around it. Compiler is designed to read and write files on disk based mainly on command-line arguments, while MacroProcessor is designed mainly to process Loyc trees.

How to use Compiler:

var c = new LeMP.Compiler(MessageSink.Console);
var argList = new List<string>() { @"D:\Dev\Loyc\Core\Tests\Program.cs", "--outext=out.cs" };
var options = c.ProcessArguments(argList, true, true);
// Look for --help in options list
if (!LeMP.Compiler.MaybeShowHelp(options, LeMP.Compiler.KnownOptions))

How to use MacroProcessor: (two ways)

var MP = new LeMP.MacroProcessor(typeof(LeMP.Prelude.BuiltinMacros), MessageSink.Console);
MP.PreOpenedNamespaces.Add((Symbol) "LeMP");
MP.PreOpenedNamespaces.Add((Symbol) "LeMP.Prelude");

// Approach #1: directly feed it Loyc trees
var code = EcsLanguageService.Value.Parse("double Sqrt(notnull double x) ==> Math.Sqrt;");
var output = MP.ProcessSynchronously(LNode.List(code));

// Approach #2: use an InputOutput object (produces an output file by default)
// (this will set the #inputFolder and #inputFileName properties, unlike Approach 1)
UString code = "double Sqrt(notnull double x) ==> Math.Sqrt;";
var io = new LeMP.InputOutput(code, "/Folder/FileName.ecs", EcsLanguageService.Value, 
	EcsLanguageService.Value.Printer, "OutputFile.cs");
// Note: you could call ProcessParallel in case there are multiple input files
MP.ProcessSynchronously(ListExt.Single(io), io2 => {

In either case you’ll probably need references to

LeMP itself references all these plus Loyc.Utilities.dll (for UG.ProcessCommandLineArguments)

Q. My question isn’t here!

Please leave your question on StackOverflow with the lemp tag and I’ll receive a notification. You can also reach me by email at gmail.com, with account name qwertie256, or make an issue on GitHub.