Add support for built-ins, starting with 'echo'

* geesh/built-ins/echo.scm: New file.
* geesh/built-ins.scm: New file.
* Makefile.scm: Add them.
* geesh/shell.scm (exec-let): Include built-ins in command search.
* tests/shell.scm: Add a test for this.

Makefile.am

@@ -37,6 +37,8 @@ endif # HAVE_GENHTML
 test-list: ; @echo $(TESTS)
 
 MODULES =                                       \
+  geesh/built-ins/echo.scm                      \
+  geesh/built-ins.scm                           \
   geesh/environment.scm                         \
   geesh/lexer.scm                               \
   geesh/parser.scm                              \

geesh/built-ins.scm

@@ -0,0 +1,80 @@
+;;; 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)
+  #:use-module (geesh built-ins echo)
+  #:export (search-built-ins
+            search-special-built-ins))
+
+;;; Commentary:
+;;;
+;;; This module provides built-in searching functions.
+;;;
+;;; Code:
+
+(define (undefined env . args)
+  (throw 'undefined-built-in))
+
+;; Special built-ins take precedence over any other command.
+(define *special-built-ins*
+  `(("." . ,undefined)
+    (":" . ,undefined)
+    ("break" . ,undefined)
+    ("continue" . ,undefined)
+    ("eval" . ,undefined)
+    ("exec" . ,undefined)
+    ("exit" . ,undefined)
+    ("export" . ,undefined)
+    ("readonly" . ,undefined)
+    ("return" . ,undefined)
+    ("set" . ,undefined)
+    ("shift" . ,undefined)
+    ("times" . ,undefined)
+    ("trap" . ,undefined)
+    ("unset" . ,undefined)))
+
+;; Regular built-ins take precendence over utilities in the search
+;; path, but not over functions.
+(define *built-ins*
+  `( ;; POSIX-specified built-ins.
+    ("alias" . ,undefined)
+    ("bg" . ,undefined)
+    ("cd" . ,undefined)
+    ("command" . ,undefined)
+    ("false" . ,undefined)
+    ("fc" . ,undefined)
+    ("fg" . ,undefined)
+    ("getopts" . ,undefined)
+    ("hash" . ,undefined)
+    ("jobs" . ,undefined)
+    ("kill" . ,undefined)
+    ("newgrp" . ,undefined)
+    ("pwd" . ,undefined)
+    ("read" . ,undefined)
+    ("true" . ,undefined)
+    ("umask" . ,undefined)
+    ("unalias" . ,undefined)
+    ("wait" . ,undefined)
+    ;; Other built-ins.
+    ("echo" . ,echo)))
+
+(define (search-special-built-ins name)
+  (assoc-ref *special-built-ins* name))
+
+(define (search-built-ins name)
+  (assoc-ref *built-ins* name))

geesh/built-ins/echo.scm

@@ -0,0 +1,30 @@
+;;; 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 echo)
+  #:export (echo))
+
+;;; Commentary:
+;;;
+;;; The 'echo' utility.
+;;;
+;;; Code:
+
+(define (echo env . args)
+  (display (string-join args " "))
+  (newline))

geesh/shell.scm

@@ -1,4 +1,5 @@
 (define-module (geesh shell)
+  #:use-module (geesh built-ins)
   #:use-module (geesh environment)
   #:use-module (ice-9 match)
   #:export (sh:exec-let
@@ -47,7 +48,19 @@ it cannot be found, return @code{#f}."
   "Find and execute @var{name} with arguments @var{args}, environment
 @var{env}, and extra environment variable bindings @var{bindings}."
   (if (slashless? name)
-      (or (and=> (find-utility env name)
+      (or (and=> (search-special-built-ins name)
+                 (lambda (proc)
+                   (for-each (match-lambda
+                               ((name . value)
+                                (set-var! env name value)))
+                             bindings)
+                   (apply proc env args)))
+          ;; TODO: Functions.
+          (and=> (search-built-ins name)
+                 (lambda (proc)
+                   ;; TODO: Use 'bindings' here.
+                   (apply proc env args)))
+          (and=> (find-utility env name)
                  (lambda (path)
                    (exec-utility env bindings path name args)))
           (error "Command not found."))

tests/shell.scm

@@ -120,4 +120,11 @@
              (('misc-error _ _ ("Command not found.") _) #t)
              (_ #f))))))))
 
+(test-equal "Executes regular built-ins"
+  "foo bar\n"
+  (let ((env (make-environment '())))
+    (with-output-to-string
+      (lambda ()
+        (sh:exec env "echo" "foo" "bar")))))
+
 (test-end)