Add more syscall-using system functions

PRIMITIVES.md

@@ -215,6 +215,8 @@ The implementation of these primitives can be found in the file [stdlib.slisp](s
   * Does the given string look like a binary number, with 0b-prefix?
 * `binary`
   * Parse the given string, with 0b-prefix, as a binary number and return the integer value.
+* `cd`
+  * Change the present working directory.  (Lookup the value with `pwd`.)
 * `dec2binary`
   * Convert an integer to a string containing the binary version of that number (e.g. 7 -> 0b111)
 * `dec2hex`
@@ -256,10 +258,18 @@ The implementation of these primitives can be found in the file [stdlib.slisp](s
 * `getenv`
   * Return the value of the given environmental variable, nor NIL if not found.
   * Uses `environment`.
+* `getgid`
+  * Return the group ID of the current user.
+* `getpid`
+  * Return the current process ID.
+* `getuid`
+  * Return the ID of the current user.
 * `hex?`
   * Does the given string look like a hex number, with 0x prefix?
 * `hex`
   * Parse the given string, with 0x-prefix, as a hex number and return the integer value.
+* `hostname`
+  * Return the system hostname.
 * `join`
   * Join all (string) items of a list into a single string.
 * `join-by`
@@ -314,6 +324,8 @@ The implementation of these primitives can be found in the file [stdlib.slisp](s
   * Print "anything" by invoking `print`, then outputting a newline.
 * `putc`
   * Print the given character.
+* `pwd`
+  * Return the present working directory.  (Change with `cd`.)
 * `random`
   * Return a random integer between zero and N-1.
 * `random_string`

stdlib.slisp

@@ -1233,6 +1233,13 @@ Incrementing by the given step each time."
     (u64! m (* i 8) 0)
     m))
 
+(defconst SYS_chdir 80)
+
+(defun cd (path)
+  "Change to the given working directory"
+  (if (< (syscall SYS_chdir path) 0)
+    nil 1))
+
 (defun getc ()
   "Read a single character from STDIN, and return it."
   (let ((str "s"))
@@ -1256,6 +1263,46 @@ Uses (environment) to get all environmental variables, and filters."
             (getenv-loop name (cdr xs))))
       nil))
 
+(defconst SYS_getgid 104)
+
+(defun getgid ()
+  "Return the group ID of the current user."
+  (let ((res (syscall SYS_getgid)))
+    (if (< res 0)
+      nil  res )))
+
+(defconst SYS_getpid 39)
+
+(defun getpid ()
+  "Return the process ID of the current process."
+  (let ((res (syscall SYS_getpid)))
+    (if (< res 0)
+      nil  res )))
+
+(defconst SYS_getuid 102)
+
+(defun getuid ()
+  "Return the ID of the current user."
+  (let ((res (syscall SYS_getuid)))
+    (if (< res 0)
+      nil  res )))
+
+(defconst SYS_uname 63)
+
+(defun hostname ()
+  "Return the system hostname, via the uname syscall."
+  (let ((len 1024)
+        (hst "")
+        (i 0)
+        (buf (alloc len)))
+    (if (< (syscall SYS_uname buf len) 0)
+        nil
+      (do
+       (while (!= (strat buf (+ i 65)) 0)
+         (set! hst (strcat hst (string (chr (strat buf (+ i 65))))))
+         (set! i (+ i 1)))
+        hst))))
+
 (defconst SYS_clock_gettime 228)
 
 (defun now ()
@@ -1276,6 +1323,16 @@ Uses (environment) to get all environmental variables, and filters."
     ((int?  c) (syscall 1 1 (string (chr (& 255 c))) 1))
     (t         (do (println "putc called with bogus arg") (exit 1)))))
 
+(defconst SYS_getcwd 79)
+
+(defun pwd ()
+  "Return the current working directory"
+  (let ((len 1024)
+        (buf (alloc len)))
+    (if (>= (syscall SYS_getcwd buf len) 0)
+      buf  nil)))
+
+
 (defconst SYS_getrandom 318)
 
 (defun random (n)