Merge pull request #44 from skx/43-random

Add random functions.

builtins/builtins.go

@@ -131,6 +131,7 @@ func PopulateEnvironment(env *env.Environment) {
 	env.Set("ord", &primitive.Procedure{F: ordFn, Help: helpMap["ord"]})
 	env.Set("os", &primitive.Procedure{F: osFn, Help: helpMap["os"]})
 	env.Set("print", &primitive.Procedure{F: printFn, Help: helpMap["print"]})
+	env.Set("random", &primitive.Procedure{F: randomFn, Help: helpMap["random"]})
 	env.Set("set", &primitive.Procedure{F: setFn, Help: helpMap["set"]})
 	env.Set("shell", &primitive.Procedure{F: shellFn, Help: helpMap["shell"]})
 	env.Set("sort", &primitive.Procedure{F: sortFn, Help: helpMap["sort"]})
@@ -1055,6 +1056,23 @@ func printFn(env *env.Environment, args []primitive.Primitive) primitive.Primiti
 	return primitive.String(out)
 }
 
+// randomFn implements (random).
+func randomFn(env *env.Environment, args []primitive.Primitive) primitive.Primitive {
+	if len(args) != 1 {
+		return primitive.Error("wrong number of arguments")
+	}
+
+	// ensure we received a number
+	num, ok := args[0].(primitive.Number)
+
+	if !ok {
+		return primitive.Error("argument not a number")
+	}
+
+	return primitive.Number(rand.Intn(int(num)))
+
+}
+
 // setFn is the implementation of `(set hash key val)`
 func setFn(env *env.Environment, args []primitive.Primitive) primitive.Primitive {
 

builtins/builtins_test.go

@@ -2250,6 +2250,44 @@ func TestPrint(t *testing.T) {
 	}
 }
 
+// TestRandom tests (random)
+func TestRandom(t *testing.T) {
+
+	// No arguments
+	out := randomFn(ENV, []primitive.Primitive{})
+
+	// Will lead to an error
+	e, ok := out.(primitive.Error)
+	if !ok {
+		t.Fatalf("expected error, got %v", out)
+	}
+	if !strings.Contains(string(e), "wrong number of arguments") {
+		t.Fatalf("got error, but wrong one %v", out)
+	}
+
+	// One argument, of the wrong type
+	out = randomFn(ENV, []primitive.Primitive{
+		primitive.String("Hello!"),
+	})
+
+	e, ok = out.(primitive.Error)
+	if !ok {
+		t.Fatalf("expected error, got %v", out)
+	}
+	if !strings.Contains(string(e), "not a number") {
+		t.Fatalf("got error, but wrong one %v", out)
+	}
+
+	// Now call with a number
+	out = randomFn(ENV, []primitive.Primitive{
+		primitive.Number(1),
+	})
+	_, ok2 := out.(primitive.Number)
+	if !ok2 {
+		t.Fatalf("expected string, got %v", out)
+	}
+}
+
 // TestSet tests set
 func TestSet(t *testing.T) {
 

builtins/help.txt

@@ -200,6 +200,13 @@ See also: sprintf
 Example: (print "Hello, world")
 Example: (print "Hello user %s you are %d" (getenv "USER") 32)
 %%
+random
+
+random will return a number between zero and one less than the value specified.
+
+See also: random:char random:item
+Example: (random 100) ; A number between 0 and 99
+%%
 set
 
 set updates the specified hash, setting the value given by name.

stdlib/stdlib.lisp

@@ -462,3 +462,14 @@
                           "Invoke the specified callback on every file beneath the given path."
 
                           (apply (directory:entries path) fn)))
+
+
+;; Add some simple random functions, using our "random" primitive.
+(set! random:char (fn* ()
+                       "Return a random character, from the set a-z."
+                       (let* (chars (split "abcdefghijklmnopqrstuvwxyz" ""))
+                         (random:item chars))))
+
+(set! random:item (fn* (lst:list)
+                       "Return a random element from the specified list."
+                       (nth lst (random (length lst)))))