Instead of using an environment variable named '?', we will use a
special environment field called 'status'. This lets us get rid of a
lot of number-string conversions (since an environment variable has to
have a string value).
* geesh/environment.scm (<environment>): Add a 'status' field.
(make-environment): Set it to 0 by default.
* geesh/repl.scm (run-repl): Use new field in place of '?' variable.
* geesh/shell.scm (exec-utility, sh:and, sh:exec-let, sh:for, sh:not,
sh:or, sh:pipeline, sh:subshell, sh:substitute-command): Ditto.
* geesh/word.scm (parameter-ref): New function that handles both
special parameters (e.g., '?') and variables.
(parameter-ref*): Like 'var-ref*', but for 'parameter-ref'.
(word->qword): Replace 'var-ref' and 'var-ref*' with 'parameter-ref'
and 'parameter-ref*' respectively.
Timothy Sample