Fix broken slice/setitem; cr/lf replace nl.

README.md

@@ -58,6 +58,8 @@ Lunar Logo solves that problem neatly. Note how in the example above `load` isn'
 
 Of course, now your application is driven by a whole scripting language, and that requires more care. With great power comes great responsibility.
 
+Other possible uses are as a fancy calculator (much more powerful than `expr`), or for writing Awk-style filters: Lunar Logo should handle TSV files very well indeed.
+
 History
 -------
 

lunar.go

@@ -1172,9 +1172,18 @@ var Procedures = map[string]Builtin {
 		}
 	}},
 	"item": {2, func (s *Scope, a ...interface{}) (interface{}, error) {
+		index := ParseInt(a[0])
 		switch seq := a[1].(type) {
-		case List: return seq[ParseInt(a[0])], nil
-		case string: return seq[ParseInt(a[0])], nil
+		case List:
+			if index < 0 {
+				index = len(seq) + index
+			}
+			return seq[index], nil
+		case string:
+			if index < 0 {
+				index = len(seq) + index
+			}
+			return seq[index], nil
 		default: return nil, Error{
 			"Item expects a sequence, got: " + fmt.Sprint(a[0])}
 		}
@@ -1214,7 +1223,12 @@ var Procedures = map[string]Builtin {
 		switch seq := a[2].(type) {
 		case List:
 			if limit < 0 {
-				limit = len(seq) - limit - 1
+				limit = len(seq) + limit
+			}
+			return seq[init:limit], nil
+		case string:
+			if limit < 0 {
+				limit = len(seq) + limit
 			}
 			return seq[init:limit], nil
 		default: return nil, Error{
@@ -1223,10 +1237,16 @@ var Procedures = map[string]Builtin {
 	}},
 	"setitem": {3,
 	func (s *Scope, a ...interface{}) (interface{}, error) {
+		index := ParseInt(a[0])
 		switch seq := a[1].(type) {
-		case List: return seq[ParseInt(a[0])], nil
+		case List:
+			if index < 0 {
+				index = len(seq) + index
+			}
+			seq[index] = a[2]
+			return nil, nil
 		default: return nil, Error{
-			"Item expects a list, got: " + fmt.Sprint(a[0])}
+			"Setitem expects a list, got: " + fmt.Sprint(a[0])}
 		}
 	}},
 
@@ -1257,7 +1277,10 @@ var Procedures = map[string]Builtin {
 	"tab": {0, func (s *Scope, a ...interface{}) (interface{}, error) {
 		return "\t", nil
 	}},
-	"nl": {0, func (s *Scope, a ...interface{}) (interface{}, error) {
+	"cr": {0, func (s *Scope, a ...interface{}) (interface{}, error) {
+		return "\r", nil
+	}},
+	"lf": {0, func (s *Scope, a ...interface{}) (interface{}, error) {
 		return "\n", nil
 	}},
 

lunar.py

@@ -492,7 +492,8 @@ def do_del(dictionary, key):
 	"empty": (0, lambda scope: ""),
 	"space": (0, lambda scope: " "),
 	"tab": (0, lambda scope: "\t"),
-	"nl": (0, lambda scope: "\n"),
+	"cr": (0, lambda scope: "\r"),
+	"lf": (0, lambda scope: "\n"),
 
 	"split": (1, lambda scope, s: s.split()),
 	"join": (1, lambda scope, seq: " ".join(seq)),