Merge pull request #1145 from mathjax/fix/let-order

Have \let look up macros first then delimiters, and removes \\ delimiter

Author: dpvc

ts/input/tex/base/BaseMappings.ts

@@ -348,7 +348,6 @@ new sm.DelimiterMap('delimiter', ParseMethods.delimiter, {
   '/': '/',
   '|': ['|', { texClass: TEXCLASS.ORD }],
   '.': '',
-  '\\\\': '\\',
   '\\lmoustache': '\u23B0', // non-standard
   '\\rmoustache': '\u23B1', // non-standard
   '\\lgroup': '\u27EE', // non-standard

ts/input/tex/newcommand/NewcommandMethods.ts

@@ -131,19 +131,6 @@ const NewcommandMethods: { [key: string]: ParseMethod } = {
     if (c === '\\') {
       // @test Let Bar, Let Brace Equal Stretchy
       name = NewcommandUtil.GetCSname(parser, name);
-      let macro = handlers
-        .get(HandlerType.DELIMITER)
-        .lookup('\\' + name) as Token;
-      if (macro) {
-        // @test Let Bar, Let Brace Equal Stretchy
-        NewcommandUtil.addDelimiter(
-          parser,
-          '\\' + cs,
-          macro.char,
-          macro.attributes
-        );
-        return;
-      }
       const map = handlers.get(HandlerType.MACRO).applicable(name);
       if (!map) {
         // @test Let Undefined CS
@@ -161,6 +148,19 @@ const NewcommandMethods: { [key: string]: ParseMethod } = {
         );
         return;
       }
+      let macro = handlers
+        .get(HandlerType.DELIMITER)
+        .lookup('\\' + name) as Token;
+      if (macro) {
+        // @test Let Bar, Let Brace Equal Stretchy
+        NewcommandUtil.addDelimiter(
+          parser,
+          '\\' + cs,
+          macro.char,
+          macro.attributes
+        );
+        return;
+      }
       macro = (map as sm.CharacterMap).lookup(name) as Token;
       // @test Let Relet, Let Let, Let Circular Macro
       const method = (p: TexParser) => map.parser(p, macro);