Move body and import lexers to separate files

libs/UIX.Asm/Lexer.Imports.cs

@@ -0,0 +1,49 @@
+using Microsoft.Iris.Asm.Models;
+using Sprache;
+
+namespace Microsoft.Iris.Asm;
+
+partial class Lexer
+{
+    public static readonly Parser<IImport> Import = ParseImport;
+
+    private static IResult<IImport> ParseImport(IInput input)
+    {
+        input = ConsumeWhitespace(input);
+
+        var importDirectiveResult = Parse.String(".import-")(input);
+        input = importDirectiveResult.Remainder;
+        if (!importDirectiveResult.WasSuccessful)
+            return Result.Failure<IImport>(input, "Invalid import directive", ["Expected '.import'"]);
+
+        var importTypeResult = Parse.Letter.AtLeastOnce().Text()(input);
+        input = importTypeResult.Remainder;
+        if (!importTypeResult.WasSuccessful)
+            return Result.Failure<IImport>(input, "Invalid import type", ["Expected 'ns'"]);
+
+        IImport import;
+        switch (importTypeResult.Value.ToUpperInvariant())
+        {
+            case "NS":
+                var uriResult = Uri.Token()(input);
+                input = uriResult.Remainder;
+                if (!uriResult.WasSuccessful)
+                    return Result.Failure<IImport>(input, "Invalid URI", ["Expected a valid URI"]);
+
+                input = Parse.String("as").Token()(input).Remainder;
+
+                var nameResult = AlphanumericText(input);
+                input = nameResult.Remainder;
+                if (!nameResult.WasSuccessful)
+                    return Result.Failure<IImport>(input, "Invalid namespace alias", ["Expected a valid namespace alias"]);
+
+                import = new NamespaceImport(uriResult.Value, nameResult.Value);
+                break;
+
+            default:
+                return Result.Failure<IImport>(input, $"Unknown import type '{importTypeResult.Value}'", ["Expected 'ns'"]);
+        }
+
+        return Result.Success(import, input);
+    }
+}