Add 'unset' built-in

* geesh/environment.scm (delete-environment-vars!): New public function.
(delete-environment-functions!): New public function.
* geesh/built-ins/unset.scm: New file.
* Makefile.am: Add it.
* geesh/built-ins.scm: Enable 'unset'.

Makefile.am

@@ -44,6 +44,7 @@ MODULES =                                       \
   geesh/built-ins/echo.scm                      \
   geesh/built-ins/false.scm                     \
   geesh/built-ins/read.scm                      \
+  geesh/built-ins/unset.scm                     \
   geesh/built-ins.scm                           \
   geesh/environment.scm                         \
   geesh/eval.scm                                \

geesh/built-ins.scm

@@ -46,7 +46,7 @@
     ("shift" . ,undefined)
     ("times" . ,undefined)
     ("trap" . ,undefined)
-    ("unset" . ,undefined)))
+    ("unset" . ,(@@ (geesh built-ins unset) main))))
 
 ;; Regular built-ins take precendence over utilities in the search
 ;; path, but not over functions.

geesh/built-ins/unset.scm

@@ -0,0 +1,37 @@
+;;; The Geesh Shell Interpreter
+;;; Copyright 2018 Timothy Sample <samplet@ngyro.com>
+;;;
+;;; This file is part of Geesh.
+;;;
+;;; Geesh is free software: you can redistribute it and/or modify
+;;; it under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation, either version 3 of the License, or
+;;; (at your option) any later version.
+;;;
+;;; Geesh is distributed in the hope that it will be useful,
+;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with Geesh.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (geesh built-ins unset)
+  #:use-module (geesh environment)
+  #:use-module (ice-9 match))
+
+;;; Commentary:
+;;;
+;;; The 'unset' utility.
+;;;
+;;; Code:
+
+(define (main env . args)
+  (match args
+    (("-f" . names)
+     (delete-environment-functions! env names)
+     0)
+    ((or ("-v" . names)
+         names)
+     (delete-environment-vars! env names)
+     0)))

geesh/environment.scm

@@ -27,12 +27,14 @@
             var-ref
             var-ref*
             set-var!
+            delete-environment-vars!
             environment->environ
             environ->alist
             environment-status
             set-environment-status!
             environment-function-ref
             define-environment-function!
+            delete-environment-functions!
             environment-arguments
             with-environment-arguments))
 
@@ -76,6 +78,11 @@
   (set-environment-vars! env (acons name val
                                     (environment-vars env))))
 
+(define (delete-environment-vars! env names)
+  (set-environment-vars! env (remove (match-lambda
+                                       ((key . _) (member key names)))
+                                     (environment-vars env))))
+
 (define* (environment->environ env #:optional (bindings '()))
   "Convert the environment variables from @var{env} into a list of
 @code{\"name=value\"} strings (an @dfn{environ}).  If @var{bindings}
@@ -110,6 +117,11 @@ such function, return @code{#f}."
   (set-environment-functions! env (acons name proc
                                          (environment-functions env))))
 
+(define (delete-environment-functions! env . names)
+  (set-environment-functions! env (remove (match-lambda
+                                            ((key . _) (member key names)))
+                                          (environment-functions env))))
+
 (define (with-environment-arguments env arguments thunk)
   "Call @var{thunk} with the arguments in @var{env} set to
 @var{arguments}."