path-cat: becomes variadic.

* stream.c (path_vcat): New static function.
(stream_init): Register path-cat instrinsic to path_vcat
rather than path_cat.

* tests/018/path.tl: path-cat tests: all examples from
documentation, plus others.

* txr.1: Documented existing behaviors that were not clear,
like when inputs are empty. Documented new variadic semantics.
Examples added.

3 files changed, 103 insertions, 8 deletions

diff --git a/stream.c b/stream.c
index cb853d98..fe3cc0bb 100644
--- a/stream.c
+++ b/stream.c
@@ -5116,6 +5116,25 @@ val path_cat(val dir_name, val base_name)
   return scat(lit("/"), dir_name, base_name, nao);
 }
 
+static val path_vcat(struct args *args)
+{
+  cnum ix = 0;
+
+  if (!args_more(args, ix)) {
+    return lit(".");
+  } else {
+    val accum = args_get(args, &ix);
+
+    if (!stringp(accum))
+      uw_throwf(file_error_s, lit("path-cat: ~s isn't a string"), accum, nao);
+
+    while (args_more(args, ix))
+      accum = path_cat(accum, args_get(args, &ix));
+
+    return accum;
+  }
+}
+
 val make_byte_input_stream(val obj)
 {
   val self = lit("make-byte-input-stream");
@@ -5376,7 +5395,7 @@ void stream_init(void)
   reg_fun(intern(lit("dir-name"), user_package), func_n1(dir_name));
   reg_fun(intern(lit("short-suffix"), user_package), func_n2o(short_suffix, 1));
   reg_fun(intern(lit("long-suffix"), user_package), func_n2o(long_suffix, 1));
-  reg_fun(intern(lit("path-cat"), user_package), func_n2(path_cat));
+  reg_fun(intern(lit("path-cat"), user_package), func_n0v(path_vcat));
   reg_varl(intern(lit("path-sep-chars"), user_package), static_str(path_sep_chars));
   reg_fun(intern(lit("get-indent-mode"), user_package), func_n1(get_indent_mode));
   reg_fun(intern(lit("test-set-indent-mode"), user_package), func_n3(test_set_indent_mode));
diff --git a/tests/018/path.tl b/tests/018/path.tl
index 16c44d77..96298dfd 100644
--- a/tests/018/path.tl
+++ b/tests/018/path.tl
@@ -96,3 +96,35 @@
   (base-name "a.b/" ".b") "a"
   (base-name "a.b/" ".b/") "a.b"
   (base-name "a.b/" "a.b") "a.b")
+
+(mtest
+  (path-cat "" "") ""
+  (path-cat "" ".") "."
+  (path-cat "." "") "."
+  (path-cat "." ".") "."
+  (path-cat "abc" ".") "abc"
+  (path-cat "." "abc") "abc"
+  (path-cat "./" ".") "./"
+  (path-cat "."  "./") "./"
+  (path-cat "abc/" ".") "abc/"
+  (path-cat "./" "abc") "abc"
+  (path-cat "/" ".") "/"
+  (path-cat "/" "abc") "/abc"
+  (path-cat "ab/cd" "ef") "ab/cd/ef"
+  (path-cat "a" "b" "c") "a/b/c"
+  (path-cat "a" "b" "" "c" "/") "a/b/c/")
+
+(mtest
+  (path-cat) "."
+  (path-cat 3) :error
+  (path-cat "") ""
+  (path-cat "/") "/"
+  (path-cat ".") "."
+  (path-cat "" "" "") ""
+  (path-cat "." "" "") "."
+  (path-cat "" "." "") "."
+  (path-cat "" "" ".") "."
+  (path-cat "." "." ".") "."
+  (path-cat "abc/" "/def/" "g") "abc/def/g"
+  (path-cat "abc/" "/def/" "g/") "abc/def/g/"
+  (path-cat "" "abc/" "/def/" "g/") "abc/def/g/")
diff --git a/txr.1 b/txr.1
index 3f7a0dc5..e00bc31b 100644
--- a/txr.1
+++ b/txr.1
@@ -57365,19 +57365,25 @@ extracted from this last component.
 
 .coNP Function @ path-cat
 .synb
-.mets (path-cat < dir-path << rel-path )
+.mets (path-cat >> [ dir-path <> { rel-path }*])
 .syne
 .desc
 The
 .code path-cat
-function joins the directory pathname given by the character
-string argument
+joints together zero or more paths, returning the combined path.
+All arguments are strings.
+
+The following description defines the behavior when
+.code path-cat
+is given exactly two arguments, which are interpreted as
 .meta dir-path
-with the relative pathname given by
-.metn rel-path ,
-returning the joined path.
+and
+.metn rel-path .
+A description of the variable argument semantics follows.
 
-The function is related to the functions
+Firstly, the two-argument
+.code path-cat
+is related to the functions
 .code dir-name
 and
 .code base-name
@@ -57422,6 +57428,40 @@ string is
 .meta dir-name
 itself.
 
+If
+.meta dir-path
+is an empty string, then
+.code rel-path
+is returned, and
+.IR "vice versa" .
+
+The variadic semantics of
+.code path-cat
+is as follows.
+
+If
+.code path-cat
+is called with no arguments at all, it returns the path
+.str .
+(period) denoting the relative path of the current directory.
+
+If
+.code path-cat
+is called with one argument, that argument is returned.
+
+If
+.code path-cat
+is called with three or more arguments, a left-associative reduction
+takes place using the two-argument semantics. The first two arguments
+are catenated into a single path, which is then catenated
+with the third argument, and so on.
+
+The above semantics implies that the following equivalence holds:
+
+.verb
+  [reduce-left path-cat list]  <--> [apply path-cat list]
+.brev
+
 .TP* Examples:
 
 .verb
@@ -57444,6 +57484,10 @@ itself.
   (path-cat "/" "abc")  --> "/abc"
 
   (path-cat "ab/cd" "ef")  --> "ab/cd/ef"
+
+  (path-cat "a" "b" "c")  -->  "a/b/c"
+
+  (path-cat "a" "b" "" "c" "/")  -->  "a/b/c/"
 .brev
 
 .coNP Function @ rel-path