stdlib: Implement head() and tail() functions.

diff --git a/docs/Goalfile.pod b/docs/Goalfile.pod
index 40ca73a..37f3c07 100644 (file)
--- a/docs/Goalfile.pod
+++ b/docs/Goalfile.pod
@@ -38,6 +38,14 @@ For example:
 
 Returns the filename extension.
 
+=head3 head (list)
+
+For example:
+
+ head (["a", "b", "c"]) ⇒ "a"
+
+Returns the head (first) element of the list.
+
 =head3 join (list1, list2)
 
 For example:
@@ -76,6 +84,14 @@ This function works something like make’s C<subst> function, except
 that C<from> is a regular expression, specifically a L<sed(1)>
 extended regular expression.
 
+=head3 tail (list)
+
+For example:
+
+ tail (["a", "b", "c"]) ⇒ ["b", "c"]
+
+Returns the tail (all except first) elements of the list.
+
 =head3 wildcard (pattern)
 
 For example:

diff --git a/stdlib/prelude.gl b/stdlib/prelude.gl
index 183338d..e2d0400 100644 (file)
--- a/stdlib/prelude.gl
+++ b/stdlib/prelude.gl
@@ -54,6 +54,14 @@ pure function wrap (wrapper, xs) = @{
 #----------------------------------------------------------------------
 # Text functions.
 
+# Head of a list.
+pure function head (xs) returning string = @{
+    for f in %xs; do
+        echo "$f"
+        exit 0
+    done
+}
+
 # Join two lists.
 pure function join (xs, ys) returning strings = @{
     for f in %xs %ys; do echo "$f"; done
@@ -71,6 +79,15 @@ pure function subst (from, to, text) returning string = @{
     echo %text | sed -E s/%from/$to/g
 }
 
+# Tail of a list.
+pure function tail (xs) returning strings = @{
+    drop=1
+    for f in %xs; do
+        if [ -z "$drop" ]; then echo "$f"; fi
+        drop=
+    done
+}
+
 #----------------------------------------------------------------------
 # File functions.
 

diff --git a/tests/10-function-head.gl b/tests/10-function-head.gl
new file mode 100644 (file)
index 0000000..3f94d08
--- /dev/null
+++ b/tests/10-function-head.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 head function.
+
+let xs = [ "a", "b", "c" ]
+let x = head (xs)
+
+goal all = { echo %x }

diff --git a/tests/10-function-head.sh b/tests/10-function-head.sh
new file mode 100755 (executable)
index 0000000..a7c49a9
--- /dev/null
+++ b/tests/10-function-head.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-head.gl > 10-function-head.out
+test "$(cat 10-function-head.out)" = "a"
+rm 10-function-head.out

diff --git a/tests/10-function-tail.expected b/tests/10-function-tail.expected
new file mode 100644 (file)
index 0000000..6421689
--- /dev/null
+++ b/tests/10-function-tail.expected
@@ -0,0 +1,3 @@
+b
+c c c
+d  d  d

diff --git a/tests/10-function-tail.gl b/tests/10-function-tail.gl
new file mode 100644 (file)
index 0000000..9594db1
--- /dev/null
+++ b/tests/10-function-tail.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 head function.
+
+let xs = [ "a", "b", "c c c", "d  d  d" ]
+let ys = tail (xs)
+
+goal all = { for f in %ys; do echo "$f"; done }

diff --git a/tests/10-function-tail.sh b/tests/10-function-tail.sh
new file mode 100755 (executable)
index 0000000..2eb690f
--- /dev/null
+++ b/tests/10-function-tail.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-tail.gl > 10-function-tail.out
+diff -u 10-function-tail.out 10-function-tail.expected
+rm 10-function-tail.out