stdlib: Implement last() and nth() functions.

diff --git a/docs/Goalfile.pod b/docs/Goalfile.pod
index 9031780..f586ec4 100644 (file)
--- a/docs/Goalfile.pod
+++ b/docs/Goalfile.pod
@@ -82,6 +82,22 @@ Concatenate C<list1> and C<list2>.  It's not usually necessary to use
 this function since goals automatically flattens lists within lists
 into simple lists in many cases.
 
+=head3 last (list)
+
+For example:
+
+ last (["a", "b", "c"]) ⇒ "c"
+
+Returns the last element of a list.
+
+=head3 nth (n, list)
+
+For example:
+
+ nth (1, ["a", "b", "c"]) ⇒ "b"
+
+Returns the n’th element of a list (counting from 0).
+
 =head3 read (filename)
 
 For example:

diff --git a/stdlib/prelude.gl b/stdlib/prelude.gl
index d8e523a..13ac311 100644 (file)
--- a/stdlib/prelude.gl
+++ b/stdlib/prelude.gl
@@ -82,6 +82,25 @@ pure function join (xs, ys) returning strings = @{
     for f in %xs %ys; do echo "$f"; done
 }
 
+# Last element of a list.
+pure function last (xs) returning string = @{
+    for f in %xs; do
+        r="$f"
+    done
+    echo "$r"
+}
+
+# n'th element of a list.
+pure function nth (n, xs) returning string = @{
+    i=0
+    r=
+    for f in %xs; do
+        if [ $i -eq %n ]; then r="$f"; fi
+        ((++i))
+    done
+    echo "$r"
+}
+
 # Sort + uniq a list.
 pure function sort (xs) returning strings = @{
     for f in %xs; do echo "$f"; done | sort -u

diff --git a/tests/10-function-last.gl b/tests/10-function-last.gl
new file mode 100644 (file)
index 0000000..c9a1e55
--- /dev/null
+++ b/tests/10-function-last.gl
@@ -0,0 +1,24 @@
+# Goals test.
+# Copyright (C) 2020 Richard W.M. Jones
+# Copyright (C) 2020 Red Hat Inc.
+#
+# This program 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 2 of the License, or
+# (at your option) any later version.
+#
+# This program 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 this program; if not, write to the Free Software Foundation, Inc.,
+# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+# Test the last function.
+
+let xs = [ "a", "b", "c" ]
+let x = last (xs)
+
+goal all = { echo %x }

diff --git a/tests/10-function-last.sh b/tests/10-function-last.sh
new file mode 100755 (executable)
index 0000000..2ca6784
--- /dev/null
+++ b/tests/10-function-last.sh
@@ -0,0 +1,24 @@
+#!/usr/bin/env bash
+# Goals test.
+# Copyright (C) 2020 Richard W.M. Jones
+# Copyright (C) 2020 Red Hat Inc.
+#
+# This program 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 2 of the License, or
+# (at your option) any later version.
+#
+# This program 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 this program; if not, write to the Free Software Foundation, Inc.,
+# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+set -e
+
+goals -f 10-function-last.gl > 10-function-last.out
+test "$(cat 10-function-last.out)" = "c"
+rm 10-function-last.out

diff --git a/tests/10-function-nth.gl b/tests/10-function-nth.gl
new file mode 100644 (file)
index 0000000..87eedd9
--- /dev/null
+++ b/tests/10-function-nth.gl
@@ -0,0 +1,24 @@
+# Goals test.
+# Copyright (C) 2020 Richard W.M. Jones
+# Copyright (C) 2020 Red Hat Inc.
+#
+# This program 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 2 of the License, or
+# (at your option) any later version.
+#
+# This program 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 this program; if not, write to the Free Software Foundation, Inc.,
+# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+# Test the nth function.
+
+let xs = [ "a", "b", "c" ]
+let x = nth ("1", xs)
+
+goal all = { echo %x }

diff --git a/tests/10-function-nth.sh b/tests/10-function-nth.sh
new file mode 100755 (executable)
index 0000000..845c686
--- /dev/null
+++ b/tests/10-function-nth.sh
@@ -0,0 +1,24 @@
+#!/usr/bin/env bash
+# Goals test.
+# Copyright (C) 2020 Richard W.M. Jones
+# Copyright (C) 2020 Red Hat Inc.
+#
+# This program 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 2 of the License, or
+# (at your option) any later version.
+#
+# This program 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 this program; if not, write to the Free Software Foundation, Inc.,
+# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+set -e
+
+goals -f 10-function-nth.gl > 10-function-nth.out
+test "$(cat 10-function-nth.out)" = "b"
+rm 10-function-nth.out