- experimenting with making "pf.lambda" immutable, neds more work
- changed logic of "pf.if" and "pf.else-if" such that they're not
  using "pf.lambda" anymore, since "pf.lambda" is immutable now
- changed usage of "pf.lambda" in "pf.for-each" since "pf.lambda" is
  immutable now
- *experimental* changes