I use TCL as I use EDA SW a lot, but I found the most horrible feature of TCLs language design, comments are not comments. A comment is a command to ignore the line. However a comment with a curly brace in it can break control flow, as its partially interpreted. I found this by commenting out some code (that was malformed) and my tcl program failed to run. I ended up commenting out the entire program save one line and still I got errors. Then I realised to my horror the comments with braces were actually affecting control flow!

That said, in EDA in general it works well for the most part.