echo $(echo $HOM) in eshell of win10 platform get void function reported

Question

I am working on emacs-27.1 of windows 10.

PS C:\Users\gaowei> emacs.exe --version
GNU Emacs 27.1

Within the eshell, I tried:

~/.doom.d [master] λ which echo
eshell/echo is a compiled Lisp function in ‘em-basic.el’.

~/.doom.d [master] λ echo $HOME
C:\Users\gaowei

It works properly until I run to nest the commands as:

~/.doom.d [master] λ echo $(echo $HOM)
Symbol’s function definition is void: echo

What's the problem? echo does exist in eshell but report void function.

Answer 1

That's syntax of eshell eshell documentation which is intended to be an alternative to the IELM.
So () is designed for elisp functions to distinguish commands.

λ (sqrt 11)
3.3166247903554

on the other hand, curly brackets are designed for commands:

λ echo ${echo $HOME}
C:\Users\me