-

[~/.elvish]─[⎇ master]─[✎ ]─> cat lib/test.elv 
modvar = a

fn test [arg]{
  echo "echo arg=$arg" > /tmp/sourced0.elv
  -source /tmp/sourced0.elv
  fnvar = b
  echo "echo fnvar=$fnvar" > /tmp/sourced1.elv
  -source /tmp/sourced1.elv
  echo "echo modvar=$modvar" > /tmp/sourced2.elv
  -source /tmp/sourced2.elv
}
[~/.elvish]─[⎇ master]─[✎ ]─> use test
[~/.elvish]─[⎇ master]─[✎ ]─> test:test argval
arg=argval
fnvar=b
Exception: Compilation error: variable $modvar not found
/tmp/sourced2.elv, line 1: echo modvar=$modvar
Traceback:
  /Users/taazadi1/.elvish/lib/test.elv, line 10:
      -source /tmp/sourced2.elv
  [tty], line 1:
    test:test argval