Start #2 cycle tag

README.md

@@ -30,7 +30,8 @@ The [feature parity board](https://github.com/osteele/liquid/projects/1) lists d
 
 In brief, these aren't implemented:
 
-- The `cycle` and `tablerow` tags
+- The group property of the `cycle` tag
+- The `tablerow` tag
 - `{% when a or b %}`
 - Loop ranges `{% for a in 1...10 %}`
 - Error modes

expression/expressions.y

@@ -16,15 +16,17 @@ func init() {
    name     string
    val      interface{}
    f        func(Context) interface{}
+   arglist  []func(Context) interface{}
    loopmods loopModifiers
    filter_params []valueFn
 }
 %type <f> expr rel filtered cond loop
 %type<filter_params> filter_params
 %type<loopmods> loop_modifiers
+%type<arglist> arglist moreargs
 %token <val> LITERAL
 %token <name> IDENTIFIER KEYWORD PROPERTY
-%token ASSIGN LOOP
+%token ARGLIST ASSIGN LOOP
 %token EQ NEQ GE LE FOR IN AND OR CONTAINS
 %left '.' '|'
 %left '<' '>'
@@ -38,10 +40,27 @@ start:
 		return nil
 	}
 }
-| LOOP loop { yylex.(*lexer).val = $2 }
+| ARGLIST arglist ';' {
+	args := $2
+	yylex.(*lexer).val = func(ctx Context) interface{} {
+		result := make([]interface{}, len(args))
+		for i, fn := range args {
+			result[i] = fn(ctx)
+		}
+		return result
+	}
+}
+| LOOP loop  ';' { yylex.(*lexer).val = $2 }
 ;
 
-loop: IDENTIFIER IN filtered loop_modifiers ';' {
+arglist:
+  expr moreargs { $$ = append([]func(Context) interface{}{$1}, $2...) };
+
+moreargs : /* empty */ { $$ = []func(Context) interface{}{}}
+| ',' expr moreargs  { $$ = append([]func(Context) interface{}{$2}, $3...) }
+;
+
+loop: IDENTIFIER IN filtered loop_modifiers {
 	name, expr, mods := $1, $3, $4
 	$$ = func(ctx Context) interface{} {
 		return &Loop{name, expr(ctx), mods}

expression/parser_test.go

@@ -7,8 +7,14 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-var parseTests = []struct{ in, expected string }{
+var parseTests = []struct {
-	{"a | filter: b", "parse error"},
+	in     string
+	expect interface{}
+}{
+	{`a | filter: b`, 3},
+	{`%assign a = 3`, nil},
+	{`{%cycle 'a'`, []interface{}{"a"}},
+	{`{%cycle 'a', 'b'`, []interface{}{"a", "b"}},
 }
 
 var parseErrorTests = []struct{ in, expected string }{
@@ -25,7 +31,7 @@ func TestParse(t *testing.T) {
 			require.NoError(t, err, test.in)
 			value, err := expr.Evaluate(ctx)
 			require.NoError(t, err, test.in)
-			require.Equal(t, 3, value, test.in)
+			require.Equal(t, test.expect, value, test.in)
 		})
 	}
 }

expression/scanner.go

@@ -10,186 +10,207 @@ var _expression_actions []byte = []byte{
 	1, 16, 1, 17, 1, 18, 1, 19,
 	1, 20, 1, 21, 1, 22, 1, 23,
 	1, 24, 1, 25, 1, 26, 1, 27,
-	1, 28, 2, 2, 3, 2, 2, 4,
+	1, 28, 1, 29, 2, 2, 3, 2,
-	2, 2, 5, 2, 2, 6, 2, 2,
+	2, 4, 2, 2, 5, 2, 2, 6,
-	7, 2, 2, 8, 2, 2, 9, 2,
+	2, 2, 7, 2, 2, 8, 2, 2,
-	2, 10,
+	9, 2, 2, 10,
 }
 
 var _expression_key_offsets []int16 = []int16{
 	0, 1, 2, 3, 4, 5, 6, 7,
-	8, 9, 10, 12, 38, 41, 42, 43,
+	8, 9, 10, 11, 12, 14, 15, 16,
-	45, 46, 49, 51, 54, 62, 71, 80,
+	17, 18, 19, 20, 47, 50, 51, 52,
-	81, 82, 83, 93, 94, 105, 116, 127,
+	54, 55, 58, 60, 63, 71, 80, 89,
-	138, 149, 160, 171, 182, 193, 205, 216,
+	90, 91, 92, 102, 103, 114, 125, 136,
-	227, 238, 249, 260, 271, 282, 293, 304,
+	147, 158, 169, 180, 191, 202, 214, 225,
+	236, 247, 258, 269, 280, 291, 302, 313,
+	324,
 }
 
 var _expression_trans_keys []byte = []byte{
-	34, 115, 115, 105, 103, 110, 111, 111,
+	34, 115, 115, 105, 103, 110, 32, 111,
-	112, 39, 48, 57, 32, 33, 34, 37,
+	111, 112, 32, 39, 48, 57, 99, 121,
+	99, 108, 101, 32, 32, 33, 34, 37,
 	39, 45, 46, 60, 61, 62, 95, 97,
-	99, 102, 105, 110, 111, 116, 9, 13,
+	99, 102, 105, 110, 111, 116, 123, 9,
-	48, 57, 65, 90, 98, 122, 32, 9,
+	13, 48, 57, 65, 90, 98, 122, 32,
-	13, 61, 34, 97, 108, 39, 46, 48,
+	9, 13, 61, 34, 97, 108, 39, 46,
-	57, 48, 57, 46, 48, 57, 45, 95,
+	48, 57, 48, 57, 46, 48, 57, 45,
-	48, 57, 65, 90, 97, 122, 45, 63,
 	95, 48, 57, 65, 90, 97, 122, 45,
 	63, 95, 48, 57, 65, 90, 97, 122,
-	61, 61, 61, 45, 58, 63, 95, 48,
+	45, 63, 95, 48, 57, 65, 90, 97,
-	57, 65, 90, 97, 122, 58, 45, 58,
+	122, 61, 61, 61, 45, 58, 63, 95,
-	63, 95, 110, 48, 57, 65, 90, 97,
+	48, 57, 65, 90, 97, 122, 58, 45,
-	122, 45, 58, 63, 95, 100, 48, 57,
-	65, 90, 97, 122, 45, 58, 63, 95,
-	111, 48, 57, 65, 90, 97, 122, 45,
 	58, 63, 95, 110, 48, 57, 65, 90,
-	97, 122, 45, 58, 63, 95, 116, 48,
+	97, 122, 45, 58, 63, 95, 100, 48,
 	57, 65, 90, 97, 122, 45, 58, 63,
-	95, 97, 48, 57, 65, 90, 98, 122,
+	95, 111, 48, 57, 65, 90, 97, 122,
-	45, 58, 63, 95, 105, 48, 57, 65,
+	45, 58, 63, 95, 110, 48, 57, 65,
-	90, 97, 122, 45, 58, 63, 95, 110,
+	90, 97, 122, 45, 58, 63, 95, 116,
 	48, 57, 65, 90, 97, 122, 45, 58,
-	63, 95, 115, 48, 57, 65, 90, 97,
+	63, 95, 97, 48, 57, 65, 90, 98,
-	122, 45, 58, 63, 95, 97, 111, 48,
+	122, 45, 58, 63, 95, 105, 48, 57,
-	57, 65, 90, 98, 122, 45, 58, 63,
+	65, 90, 97, 122, 45, 58, 63, 95,
-	95, 108, 48, 57, 65, 90, 97, 122,
+	110, 48, 57, 65, 90, 97, 122, 45,
-	45, 58, 63, 95, 115, 48, 57, 65,
+	58, 63, 95, 115, 48, 57, 65, 90,
-	90, 97, 122, 45, 58, 63, 95, 101,
+	97, 122, 45, 58, 63, 95, 97, 111,
+	48, 57, 65, 90, 98, 122, 45, 58,
+	63, 95, 108, 48, 57, 65, 90, 97,
+	122, 45, 58, 63, 95, 115, 48, 57,
+	65, 90, 97, 122, 45, 58, 63, 95,
+	101, 48, 57, 65, 90, 97, 122, 45,
+	58, 63, 95, 114, 48, 57, 65, 90,
+	97, 122, 45, 58, 63, 95, 110, 48,
+	57, 65, 90, 97, 122, 45, 58, 63,
+	95, 105, 48, 57, 65, 90, 97, 122,
+	45, 58, 63, 95, 108, 48, 57, 65,
+	90, 97, 122, 45, 58, 63, 95, 114,
 	48, 57, 65, 90, 97, 122, 45, 58,
 	63, 95, 114, 48, 57, 65, 90, 97,
-	122, 45, 58, 63, 95, 110, 48, 57,
+	122, 45, 58, 63, 95, 117, 48, 57,
-	65, 90, 97, 122, 45, 58, 63, 95,
+	65, 90, 97, 122, 37,
-	105, 48, 57, 65, 90, 97, 122, 45,
-	58, 63, 95, 108, 48, 57, 65, 90,
-	97, 122, 45, 58, 63, 95, 114, 48,
-	57, 65, 90, 97, 122, 45, 58, 63,
-	95, 114, 48, 57, 65, 90, 97, 122,
-	45, 58, 63, 95, 117, 48, 57, 65,
-	90, 97, 122,
 }
 
 var _expression_single_lengths []byte = []byte{
 	1, 1, 1, 1, 1, 1, 1, 1,
-	1, 1, 0, 18, 1, 1, 1, 2,
+	1, 1, 1, 1, 0, 1, 1, 1,
+	1, 1, 1, 19, 1, 1, 1, 2,
 	1, 1, 0, 1, 2, 3, 3, 1,
 	1, 1, 4, 1, 5, 5, 5, 5,
 	5, 5, 5, 5, 5, 6, 5, 5,
 	5, 5, 5, 5, 5, 5, 5, 5,
+	1,
 }
 
 var _expression_range_lengths []byte = []byte{
 	0, 0, 0, 0, 0, 0, 0, 0,
-	0, 0, 1, 4, 1, 0, 0, 0,
+	0, 0, 0, 0, 1, 0, 0, 0,
+	0, 0, 0, 4, 1, 0, 0, 0,
 	0, 1, 1, 1, 3, 3, 3, 0,
 	0, 0, 3, 0, 3, 3, 3, 3,
 	3, 3, 3, 3, 3, 3, 3, 3,
 	3, 3, 3, 3, 3, 3, 3, 3,
+	0,
 }
 
 var _expression_index_offsets []int16 = []int16{
 	0, 2, 4, 6, 8, 10, 12, 14,
-	16, 18, 20, 22, 45, 48, 50, 52,
+	16, 18, 20, 22, 24, 26, 28, 30,
-	55, 57, 60, 62, 65, 71, 78, 85,
+	32, 34, 36, 38, 62, 65, 67, 69,
-	87, 89, 91, 99, 101, 110, 119, 128,
+	72, 74, 77, 79, 82, 88, 95, 102,
-	137, 146, 155, 164, 173, 182, 192, 201,
+	104, 106, 108, 116, 118, 127, 136, 145,
-	210, 219, 228, 237, 246, 255, 264, 273,
+	154, 163, 172, 181, 190, 199, 209, 218,
+	227, 236, 245, 254, 263, 272, 281, 290,
+	299,
 }
 
 var _expression_indicies []byte = []byte{
 	2, 1, 3, 0, 4, 0, 5, 0,
 	6, 0, 7, 0, 8, 0, 9, 0,
-	10, 0, 2, 11, 12, 0, 14, 15,
+	10, 0, 11, 0, 12, 0, 2, 13,
-	16, 17, 18, 19, 20, 22, 23, 24,
+	14, 0, 15, 0, 16, 0, 17, 0,
-	25, 26, 27, 28, 29, 30, 31, 32,
+	18, 0, 19, 0, 20, 0, 22, 23,
-	14, 21, 25, 25, 13, 14, 14, 33,
+	24, 25, 26, 27, 28, 30, 31, 32,
-	35, 34, 2, 1, 36, 37, 34, 2,
+	33, 34, 35, 36, 37, 38, 39, 40,
-	11, 38, 21, 34, 12, 39, 12, 21,
+	41, 22, 29, 33, 33, 21, 22, 22,
-	40, 41, 41, 42, 41, 41, 34, 41,
+	42, 44, 43, 2, 1, 45, 46, 43,
-	44, 41, 41, 41, 41, 43, 41, 44,
+	2, 13, 47, 29, 43, 14, 48, 14,
-	41, 42, 41, 41, 39, 45, 34, 46,
+	29, 49, 50, 50, 51, 50, 50, 43,
-	34, 47, 34, 25, 49, 50, 25, 25,
+	50, 53, 50, 50, 50, 50, 52, 50,
-	25, 25, 48, 49, 51, 25, 49, 50,
+	53, 50, 51, 50, 50, 48, 54, 43,
-	25, 52, 25, 25, 25, 51, 25, 49,
+	55, 43, 56, 43, 33, 58, 59, 33,
-	50, 25, 53, 25, 25, 25, 51, 25,
+	33, 33, 33, 57, 58, 60, 33, 58,
-	49, 50, 25, 54, 25, 25, 25, 51,
+	59, 33, 61, 33, 33, 33, 60, 33,
-	25, 49, 50, 25, 55, 25, 25, 25,
+	58, 59, 33, 62, 33, 33, 33, 60,
-	51, 25, 49, 50, 25, 56, 25, 25,
+	33, 58, 59, 33, 63, 33, 33, 33,
-	25, 51, 25, 49, 50, 25, 57, 25,
+	60, 33, 58, 59, 33, 64, 33, 33,
-	25, 25, 51, 25, 49, 50, 25, 58,
+	33, 60, 33, 58, 59, 33, 65, 33,
-	25, 25, 25, 51, 25, 49, 50, 25,
+	33, 33, 60, 33, 58, 59, 33, 66,
-	59, 25, 25, 25, 51, 25, 49, 50,
+	33, 33, 33, 60, 33, 58, 59, 33,
-	25, 60, 25, 25, 25, 51, 25, 49,
+	67, 33, 33, 33, 60, 33, 58, 59,
-	50, 25, 61, 62, 25, 25, 25, 51,
+	33, 68, 33, 33, 33, 60, 33, 58,
-	25, 49, 50, 25, 63, 25, 25, 25,
+	59, 33, 69, 33, 33, 33, 60, 33,
-	51, 25, 49, 50, 25, 64, 25, 25,
+	58, 59, 33, 70, 71, 33, 33, 33,
-	25, 51, 25, 49, 50, 25, 65, 25,
+	60, 33, 58, 59, 33, 72, 33, 33,
-	25, 25, 51, 25, 49, 50, 25, 66,
+	33, 60, 33, 58, 59, 33, 73, 33,
-	25, 25, 25, 51, 25, 49, 50, 25,
+	33, 33, 60, 33, 58, 59, 33, 74,
-	67, 25, 25, 25, 51, 25, 49, 50,
+	33, 33, 33, 60, 33, 58, 59, 33,
-	25, 68, 25, 25, 25, 51, 25, 49,
+	75, 33, 33, 33, 60, 33, 58, 59,
-	50, 25, 69, 25, 25, 25, 51, 25,
+	33, 76, 33, 33, 33, 60, 33, 58,
-	49, 50, 25, 70, 25, 25, 25, 51,
+	59, 33, 77, 33, 33, 33, 60, 33,
-	25, 49, 50, 25, 71, 25, 25, 25,
+	58, 59, 33, 78, 33, 33, 33, 60,
-	51, 25, 49, 50, 25, 64, 25, 25,
+	33, 58, 59, 33, 79, 33, 33, 33,
-	25, 51,
+	60, 33, 58, 59, 33, 80, 33, 33,
+	33, 60, 33, 58, 59, 33, 73, 33,
+	33, 33, 60, 81, 43,
 }
 
 var _expression_trans_targs []byte = []byte{
-	11, 0, 11, 2, 3, 4, 5, 11,
+	19, 0, 19, 2, 3, 4, 5, 6,
-	7, 8, 11, 9, 18, 11, 12, 13,
+	19, 8, 9, 10, 19, 11, 26, 14,
-	14, 15, 16, 17, 20, 19, 23, 24,
+	15, 16, 17, 18, 19, 19, 20, 21,
-	25, 26, 28, 30, 37, 42, 43, 45,
+	22, 23, 24, 25, 28, 27, 31, 32,
-	46, 11, 11, 11, 1, 6, 10, 11,
+	33, 34, 36, 38, 45, 50, 51, 53,
-	11, 21, 22, 11, 11, 11, 11, 11,
+	54, 56, 19, 19, 19, 1, 7, 12,
-	11, 11, 27, 11, 29, 26, 31, 32,
+	19, 19, 29, 30, 19, 19, 19, 19,
-	33, 34, 35, 36, 26, 38, 41, 39,
+	19, 19, 19, 35, 19, 37, 34, 39,
-	40, 26, 26, 26, 44, 26, 26, 47,
+	40, 41, 42, 43, 44, 34, 46, 49,
+	47, 48, 34, 34, 34, 52, 34, 34,
+	55, 13,
 }
 
 var _expression_trans_actions []byte = []byte{
-	39, 0, 11, 0, 0, 0, 0, 7,
+	41, 0, 13, 0, 0, 0, 0, 0,
-	0, 0, 9, 0, 0, 25, 0, 0,
+	7, 0, 0, 0, 11, 0, 0, 0,
+	0, 0, 0, 0, 9, 27, 0, 0,
 	5, 5, 5, 5, 0, 0, 0, 0,
-	0, 64, 0, 0, 0, 0, 0, 0,
+	0, 66, 0, 0, 0, 0, 0, 0,
-	0, 35, 37, 15, 0, 0, 0, 29,
+	0, 5, 37, 39, 17, 0, 0, 0,
-	27, 0, 0, 33, 23, 19, 13, 17,
+	31, 29, 0, 0, 35, 25, 21, 15,
-	41, 21, 0, 31, 0, 49, 0, 0,
+	19, 43, 23, 0, 33, 0, 51, 0,
-	0, 0, 0, 0, 55, 0, 0, 0,
+	0, 0, 0, 0, 0, 57, 0, 0,
-	0, 43, 58, 61, 0, 46, 52, 0,
+	0, 0, 45, 60, 63, 0, 48, 54,
+	0, 0,
 }
 
 var _expression_to_state_actions []byte = []byte{
+	0, 0, 0, 0, 0, 0, 0, 0,
 	0, 0, 0, 0, 0, 0, 0, 0,
 	0, 0, 0, 1, 0, 0, 0, 0,
 	0, 0, 0, 0, 0, 0, 0, 0,
 	0, 0, 0, 0, 0, 0, 0, 0,
 	0, 0, 0, 0, 0, 0, 0, 0,
 	0, 0, 0, 0, 0, 0, 0, 0,
+	0,
 }
 
 var _expression_from_state_actions []byte = []byte{
+	0, 0, 0, 0, 0, 0, 0, 0,
 	0, 0, 0, 0, 0, 0, 0, 0,
 	0, 0, 0, 3, 0, 0, 0, 0,
 	0, 0, 0, 0, 0, 0, 0, 0,
 	0, 0, 0, 0, 0, 0, 0, 0,
 	0, 0, 0, 0, 0, 0, 0, 0,
 	0, 0, 0, 0, 0, 0, 0, 0,
+	0,
 }
 
 var _expression_eof_trans []int16 = []int16{
 	1, 1, 1, 1, 1, 1, 1, 1,
-	1, 1, 1, 0, 34, 35, 35, 35,
+	1, 1, 1, 1, 1, 1, 1, 1,
-	35, 35, 40, 41, 35, 44, 40, 35,
+	1, 1, 1, 0, 43, 44, 44, 44,
-	35, 35, 49, 52, 52, 52, 52, 52,
+	44, 44, 49, 50, 44, 53, 49, 44,
-	52, 52, 52, 52, 52, 52, 52, 52,
+	44, 44, 58, 61, 61, 61, 61, 61,
-	52, 52, 52, 52, 52, 52, 52, 52,
+	61, 61, 61, 61, 61, 61, 61, 61,
+	61, 61, 61, 61, 61, 61, 61, 61,
+	44,
 }
 
-const expression_start int = 11
+const expression_start int = 19
-const expression_first_final int = 11
+const expression_first_final int = 19
 const expression_error int = -1
 
-const expression_en_main int = 11
+const expression_en_main int = 19
 
 //line scanner.rl:11
 
@@ -210,7 +231,7 @@ func newLexer(data []byte) *lexer {
 		pe:   len(data),
 	}
 
-//line scanner.go:218
+//line scanner.go:239
 	{
 		lex.cs = expression_start
 		lex.ts = 0
@@ -226,7 +247,7 @@ func (lex *lexer) Lex(out *yySymType) int {
 	eof := lex.pe
 	tok := 0
 
-//line scanner.go:235
+//line scanner.go:256
 	{
 		var _klen int
 		var _trans int
@@ -247,7 +268,7 @@ func (lex *lexer) Lex(out *yySymType) int {
 //line NONE:1
 				lex.ts = (lex.p)
 
-//line scanner.go:255
+//line scanner.go:276
 			}
 		}
 
@@ -324,28 +345,28 @@ func (lex *lexer) Lex(out *yySymType) int {
 
 			case 3:
 //line scanner.rl:38
-				lex.act = 6
-			case 4:
-//line scanner.rl:88
 				lex.act = 7
+			case 4:
+//line scanner.rl:89
+				lex.act = 8
 			case 5:
-//line scanner.rl:93
-				lex.act = 12
-			case 6:
 //line scanner.rl:94
 				lex.act = 13
-			case 7:
+			case 6:
 //line scanner.rl:95
 				lex.act = 14
-			case 8:
+			case 7:
 //line scanner.rl:96
 				lex.act = 15
-			case 9:
+			case 8:
 //line scanner.rl:97
 				lex.act = 16
+			case 9:
+//line scanner.rl:98
+				lex.act = 17
 			case 10:
 //line scanner.rl:43
-				lex.act = 18
+				lex.act = 19
 			case 11:
 //line scanner.rl:82
 				lex.te = (lex.p) + 1
@@ -358,11 +379,19 @@ func (lex *lexer) Lex(out *yySymType) int {
 //line scanner.rl:83
 				lex.te = (lex.p) + 1
 				{
-					tok = LOOP
+					tok = ARGLIST
 					(lex.p)++
 					goto _out
 				}
 			case 13:
+//line scanner.rl:84
+				lex.te = (lex.p) + 1
+				{
+					tok = LOOP
+					(lex.p)++
+					goto _out
+				}
+			case 14:
 //line scanner.rl:66
 				lex.te = (lex.p) + 1
 				{
@@ -373,19 +402,11 @@ func (lex *lexer) Lex(out *yySymType) int {
 					goto _out
 
 				}
-			case 14:
-//line scanner.rl:89
-				lex.te = (lex.p) + 1
-				{
-					tok = EQ
-					(lex.p)++
-					goto _out
-				}
 			case 15:
 //line scanner.rl:90
 				lex.te = (lex.p) + 1
 				{
-					tok = NEQ
+					tok = EQ
 					(lex.p)++
 					goto _out
 				}
@@ -393,7 +414,7 @@ func (lex *lexer) Lex(out *yySymType) int {
 //line scanner.rl:91
 				lex.te = (lex.p) + 1
 				{
-					tok = GE
+					tok = NEQ
 					(lex.p)++
 					goto _out
 				}
@@ -401,12 +422,20 @@ func (lex *lexer) Lex(out *yySymType) int {
 //line scanner.rl:92
 				lex.te = (lex.p) + 1
 				{
-					tok = LE
+					tok = GE
 					(lex.p)++
 					goto _out
 				}
 			case 18:
-//line scanner.rl:98
+//line scanner.rl:93
+				lex.te = (lex.p) + 1
+				{
+					tok = LE
+					(lex.p)++
+					goto _out
+				}
+			case 19:
+//line scanner.rl:99
 				lex.te = (lex.p) + 1
 				{
 					tok = KEYWORD
@@ -414,8 +443,8 @@ func (lex *lexer) Lex(out *yySymType) int {
 					(lex.p)++
 					goto _out
 				}
-			case 19:
+			case 20:
-//line scanner.rl:100
+//line scanner.rl:101
 				lex.te = (lex.p) + 1
 				{
 					tok = PROPERTY
@@ -423,15 +452,15 @@ func (lex *lexer) Lex(out *yySymType) int {
 					(lex.p)++
 					goto _out
 				}
-			case 20:
+			case 21:
-//line scanner.rl:102
+//line scanner.rl:103
 				lex.te = (lex.p) + 1
 				{
 					tok = int(lex.data[lex.ts])
 					(lex.p)++
 					goto _out
 				}
-			case 21:
+			case 22:
 //line scanner.rl:48
 				lex.te = (lex.p)
 				(lex.p)--
@@ -446,7 +475,7 @@ func (lex *lexer) Lex(out *yySymType) int {
 					goto _out
 
 				}
-			case 22:
+			case 23:
 //line scanner.rl:57
 				lex.te = (lex.p)
 				(lex.p)--
@@ -461,7 +490,7 @@ func (lex *lexer) Lex(out *yySymType) int {
 					goto _out
 
 				}
-			case 23:
+			case 24:
 //line scanner.rl:43
 				lex.te = (lex.p)
 				(lex.p)--
@@ -472,8 +501,8 @@ func (lex *lexer) Lex(out *yySymType) int {
 					goto _out
 
 				}
-			case 24:
+			case 25:
-//line scanner.rl:100
+//line scanner.rl:101
 				lex.te = (lex.p)
 				(lex.p)--
 				{
@@ -482,32 +511,32 @@ func (lex *lexer) Lex(out *yySymType) int {
 					(lex.p)++
 					goto _out
 				}
-			case 25:
-//line scanner.rl:101
-				lex.te = (lex.p)
-				(lex.p)--
-
 			case 26:
 //line scanner.rl:102
 				lex.te = (lex.p)
 				(lex.p)--
-				{
+
-					tok = int(lex.data[lex.ts])
-					(lex.p)++
-					goto _out
-				}
 			case 27:
-//line scanner.rl:102
+//line scanner.rl:103
-				(lex.p) = (lex.te) - 1
+				lex.te = (lex.p)
+				(lex.p)--
 				{
 					tok = int(lex.data[lex.ts])
 					(lex.p)++
 					goto _out
 				}
 			case 28:
+//line scanner.rl:103
+				(lex.p) = (lex.te) - 1
+				{
+					tok = int(lex.data[lex.ts])
+					(lex.p)++
+					goto _out
+				}
+			case 29:
 //line NONE:1
 				switch lex.act {
-				case 6:
+				case 7:
 					{
 						(lex.p) = (lex.te) - 1
 
@@ -517,7 +546,7 @@ func (lex *lexer) Lex(out *yySymType) int {
 						goto _out
 
 					}
-				case 7:
+				case 8:
 					{
 						(lex.p) = (lex.te) - 1
 						tok = LITERAL
@@ -525,42 +554,42 @@ func (lex *lexer) Lex(out *yySymType) int {
 						(lex.p)++
 						goto _out
 					}
-				case 12:
+				case 13:
 					{
 						(lex.p) = (lex.te) - 1
 						tok = AND
 						(lex.p)++
 						goto _out
 					}
-				case 13:
+				case 14:
 					{
 						(lex.p) = (lex.te) - 1
 						tok = OR
 						(lex.p)++
 						goto _out
 					}
-				case 14:
+				case 15:
 					{
 						(lex.p) = (lex.te) - 1
 						tok = CONTAINS
 						(lex.p)++
 						goto _out
 					}
-				case 15:
+				case 16:
 					{
 						(lex.p) = (lex.te) - 1
 						tok = FOR
 						(lex.p)++
 						goto _out
 					}
-				case 16:
+				case 17:
 					{
 						(lex.p) = (lex.te) - 1
 						tok = IN
 						(lex.p)++
 						goto _out
 					}
-				case 18:
+				case 19:
 					{
 						(lex.p) = (lex.te) - 1
 
@@ -572,7 +601,7 @@ func (lex *lexer) Lex(out *yySymType) int {
 					}
 				}
 
-//line scanner.go:513
+//line scanner.go:539
 			}
 		}
 
@@ -587,7 +616,7 @@ func (lex *lexer) Lex(out *yySymType) int {
 //line NONE:1
 				lex.ts = 0
 
-//line scanner.go:527
+//line scanner.go:553
 			}
 		}
 
@@ -610,7 +639,7 @@ func (lex *lexer) Lex(out *yySymType) int {
 		}
 	}
 
-//line scanner.rl:106
+//line scanner.rl:107
 
 	return tok
 }

expression/scanner.rl

@@ -79,8 +79,9 @@ func (lex *lexer) Lex(out *yySymType) int {
 		string = '"' (any - '"')* '"' | "'" (any - "'")* "'" ; # TODO escapes
 
 		main := |*
-			"%assign" => { tok = ASSIGN; fbreak; };
+			"%assign " => { tok = ASSIGN; fbreak; };
-			"%loop" => { tok = LOOP; fbreak; };
+			"{%cycle " => { tok = ARGLIST; fbreak; };
+			"%loop " => { tok = LOOP; fbreak; };
 			int => Int;
 			float => Float;
 			string => String;

expression/scanner_test.go

@@ -83,4 +83,7 @@ func TestLex(t *testing.T) {
 	require.Equal(t, "ab_c", ts[1].typ.name)
 	require.Equal(t, "ab-c", ts[2].typ.name)
 	require.Equal(t, "abc?", ts[3].typ.name)
+
+	ts, _ = scanExpression(`{%cycle 'a', 'b'`)
+	require.Len(t, ts, 4)
 }

expression/y.go

@@ -21,6 +21,7 @@ type yySymType struct {
 	name          string
 	val           interface{}
 	f             func(Context) interface{}
+	arglist       []func(Context) interface{}
 	loopmods      loopModifiers
 	filter_params []valueFn
 }
@@ -29,17 +30,18 @@ const LITERAL = 57346
 const IDENTIFIER = 57347
 const KEYWORD = 57348
 const PROPERTY = 57349
-const ASSIGN = 57350
+const ARGLIST = 57350
-const LOOP = 57351
+const ASSIGN = 57351
-const EQ = 57352
+const LOOP = 57352
-const NEQ = 57353
+const EQ = 57353
-const GE = 57354
+const NEQ = 57354
-const LE = 57355
+const GE = 57355
-const FOR = 57356
+const LE = 57356
-const IN = 57357
+const FOR = 57357
-const AND = 57358
+const IN = 57358
-const OR = 57359
+const AND = 57359
-const CONTAINS = 57360
+const OR = 57360
+const CONTAINS = 57361
 
 var yyToknames = [...]string{
 	"$end",
@@ -49,6 +51,7 @@ var yyToknames = [...]string{
 	"IDENTIFIER",
 	"KEYWORD",
 	"PROPERTY",
+	"ARGLIST",
 	"ASSIGN",
 	"LOOP",
 	"EQ",
@@ -66,11 +69,11 @@ var yyToknames = [...]string{
 	"'>'",
 	"';'",
 	"'='",
+	"','",
 	"'['",
 	"']'",
 	"'('",
 	"')'",
-	"','",
 }
 var yyStatenames = [...]string{}
 
@@ -87,60 +90,67 @@ var yyExca = [...]int{
 
 const yyPrivate = 57344
 
-const yyLast = 67
+const yyLast = 77
 
 var yyAct = [...]int{
 
-	7, 18, 51, 30, 20, 21, 24, 25, 6, 17,
+	8, 35, 21, 60, 7, 17, 23, 24, 27, 28,
-	8, 9, 26, 8, 9, 23, 22, 3, 4, 19,
+	9, 10, 33, 37, 29, 9, 10, 26, 25, 4,
-	34, 35, 36, 37, 38, 39, 40, 41, 18, 12,
+	3, 5, 22, 41, 42, 43, 44, 45, 46, 47,
-	13, 44, 44, 10, 47, 18, 10, 53, 54, 43,
+	48, 13, 14, 21, 51, 11, 21, 52, 50, 51,
-	45, 42, 12, 13, 31, 17, 19, 48, 49, 11,
+	11, 55, 21, 53, 49, 34, 20, 2, 13, 14,
-	5, 2, 55, 19, 16, 52, 32, 33, 14, 56,
+	38, 6, 36, 22, 58, 12, 22, 56, 19, 30,
-	1, 50, 27, 28, 29, 46, 15,
+	20, 63, 22, 57, 15, 31, 32, 61, 62, 39,
+	40, 64, 1, 16, 59, 54, 18,
 }
 var yyPact = [...]int{
 
-	9, -1000, 26, 53, 49, -1000, -11, -6, -1000, -1000,
+	11, -1000, 31, 59, 6, 53, -1000, 25, -5, -1000,
-	6, -1000, 6, 6, -21, -1000, 29, 51, -1000, 6,
+	-1000, 6, -1000, 6, 6, -13, 21, 26, -11, 34,
-	6, 6, 6, 6, 6, 6, 6, 13, -1000, -1000,
+	64, -1000, 6, 6, 6, 6, 6, 6, 6, 6,
-	6, 6, -1000, 6, 21, 28, 28, 28, 28, 28,
+	14, -1000, -1000, 6, -1000, -1000, 6, -1000, 6, -1000,
-	28, 28, -1000, 25, 28, -11, -27, 28, -1000, -1000,
+	6, 29, 35, 35, 35, 35, 35, 35, 35, -1000,
-	32, 6, -1000, -1000, 55, 28, -1000,
+	39, 35, 26, 25, -23, 35, -1000, -1000, -1000, 62,
+	6, -1000, 67, 35, -1000,
 }
 var yyPgo = [...]int{
 
-	0, 0, 50, 8, 51, 66, 65, 61, 60,
+	0, 0, 51, 4, 47, 76, 75, 74, 73, 1,
+	72,
 }
 var yyR1 = [...]int{
 
-	0, 8, 8, 8, 5, 7, 7, 7, 1, 1,
+	0, 10, 10, 10, 10, 8, 9, 9, 5, 7,
-	1, 1, 1, 3, 3, 3, 6, 6, 2, 2,
+	7, 7, 1, 1, 1, 1, 1, 3, 3, 3,
-	2, 2, 2, 2, 2, 2, 4, 4, 4,
+	6, 6, 2, 2, 2, 2, 2, 2, 2, 2,
+	4, 4, 4,
 }
 var yyR2 = [...]int{
 
-	0, 2, 5, 2, 5, 0, 2, 3, 1, 1,
+	0, 2, 5, 3, 3, 2, 0, 3, 4, 0,
-	2, 4, 3, 1, 3, 4, 1, 3, 1, 3,
+	2, 3, 1, 1, 2, 4, 3, 1, 3, 4,
-	3, 3, 3, 3, 3, 3, 1, 3, 3,
+	1, 3, 1, 3, 3, 3, 3, 3, 3, 3,
+	1, 3, 3,
 }
 var yyChk = [...]int{
 
-	-1000, -8, -4, 8, 9, -2, -3, -1, 4, 5,
+	-1000, -10, -4, 9, 8, 10, -2, -3, -1, 4,
-	27, 23, 16, 17, 5, -5, 5, 20, 7, 25,
+	5, 29, 24, 17, 18, 5, -8, -1, -5, 5,
-	10, 11, 22, 21, 12, 13, 18, -4, -2, -2,
+	21, 7, 27, 11, 12, 23, 22, 13, 14, 19,
-	24, 15, 5, 6, -1, -1, -1, -1, -1, -1,
+	-4, -2, -2, 25, 24, -9, 26, 24, 16, 5,
-	-1, -1, 28, -3, -1, -3, -6, -1, 26, 23,
+	6, -1, -1, -1, -1, -1, -1, -1, -1, 30,
-	-7, 29, 23, 5, 6, -1, 4,
+	-3, -1, -1, -3, -6, -1, 28, 24, -9, -7,
+	26, 5, 6, -1, 4,
 }
 var yyDef = [...]int{
 
-	0, -2, 0, 0, 0, 26, 18, 13, 8, 9,
+	0, -2, 0, 0, 0, 0, 30, 22, 17, 12,
-	0, 1, 0, 0, 0, 3, 0, 0, 10, 0,
+	13, 0, 1, 0, 0, 0, 0, 6, 0, 0,
-	0, 0, 0, 0, 0, 0, 0, 0, 27, 28,
+	0, 14, 0, 0, 0, 0, 0, 0, 0, 0,
-	0, 0, 14, 0, 0, 19, 20, 21, 22, 23,
+	0, 31, 32, 0, 3, 5, 0, 4, 0, 18,
-	24, 25, 12, 0, 13, 5, 15, 16, 11, 2,
+	0, 0, 23, 24, 25, 26, 27, 28, 29, 16,
-	0, 0, 4, 6, 0, 17, 7,
+	0, 17, 6, 9, 19, 20, 15, 2, 7, 8,
+	0, 10, 0, 21, 11,
 }
 var yyTok1 = [...]int{
 
@@ -148,20 +158,20 @@ var yyTok1 = [...]int{
 	3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
 	3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
 	3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
-	27, 28, 3, 3, 29, 3, 19, 3, 3, 3,
+	29, 30, 3, 3, 26, 3, 20, 3, 3, 3,
-	3, 3, 3, 3, 3, 3, 3, 3, 3, 23,
+	3, 3, 3, 3, 3, 3, 3, 3, 3, 24,
-	21, 24, 22, 3, 3, 3, 3, 3, 3, 3,
+	22, 25, 23, 3, 3, 3, 3, 3, 3, 3,
 	3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
 	3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
-	3, 25, 3, 26, 3, 3, 3, 3, 3, 3,
+	3, 27, 3, 28, 3, 3, 3, 3, 3, 3,
 	3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
 	3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
-	3, 3, 3, 3, 20,
+	3, 3, 3, 3, 21,
 }
 var yyTok2 = [...]int{
 
 	2, 3, 4, 5, 6, 7, 8, 9, 10, 11,
-	12, 13, 14, 15, 16, 17, 18,
+	12, 13, 14, 15, 16, 17, 18, 19,
 }
 var yyTok3 = [...]int{
 	0,
@@ -506,13 +516,13 @@ yydefault:
 
 	case 1:
 		yyDollar = yyS[yypt-2 : yypt+1]
-		//line expressions.y:33
+		//line expressions.y:35
 		{
 			yylex.(*lexer).val = yyDollar[1].f
 		}
 	case 2:
 		yyDollar = yyS[yypt-5 : yypt+1]
-		//line expressions.y:34
+		//line expressions.y:36
 		{
 			name, expr := yyDollar[2].name, yyDollar[4].f
 			yylex.(*lexer).val = func(ctx Context) interface{} {
@@ -521,29 +531,60 @@ yydefault:
 			}
 		}
 	case 3:
-		yyDollar = yyS[yypt-2 : yypt+1]
+		yyDollar = yyS[yypt-3 : yypt+1]
-		//line expressions.y:41
+		//line expressions.y:43
+		{
+			args := yyDollar[2].arglist
+			yylex.(*lexer).val = func(ctx Context) interface{} {
+				result := make([]interface{}, len(args))
+				for i, fn := range args {
+					result[i] = fn(ctx)
+				}
+				return result
+			}
+		}
+	case 4:
+		yyDollar = yyS[yypt-3 : yypt+1]
+		//line expressions.y:53
 		{
 			yylex.(*lexer).val = yyDollar[2].f
 		}
-	case 4:
+	case 5:
-		yyDollar = yyS[yypt-5 : yypt+1]
+		yyDollar = yyS[yypt-2 : yypt+1]
-		//line expressions.y:44
+		//line expressions.y:57
+		{
+			yyVAL.arglist = append([]func(Context) interface{}{yyDollar[1].f}, yyDollar[2].arglist...)
+		}
+	case 6:
+		yyDollar = yyS[yypt-0 : yypt+1]
+		//line expressions.y:59
+		{
+			yyVAL.arglist = []func(Context) interface{}{}
+		}
+	case 7:
+		yyDollar = yyS[yypt-3 : yypt+1]
+		//line expressions.y:60
+		{
+			yyVAL.arglist = append([]func(Context) interface{}{yyDollar[2].f}, yyDollar[3].arglist...)
+		}
+	case 8:
+		yyDollar = yyS[yypt-4 : yypt+1]
+		//line expressions.y:63
 		{
 			name, expr, mods := yyDollar[1].name, yyDollar[3].f, yyDollar[4].loopmods
 			yyVAL.f = func(ctx Context) interface{} {
 				return &Loop{name, expr(ctx), mods}
 			}
 		}
-	case 5:
+	case 9:
 		yyDollar = yyS[yypt-0 : yypt+1]
-		//line expressions.y:52
+		//line expressions.y:71
 		{
 			yyVAL.loopmods = loopModifiers{}
 		}
-	case 6:
+	case 10:
 		yyDollar = yyS[yypt-2 : yypt+1]
-		//line expressions.y:53
+		//line expressions.y:72
 		{
 			switch yyDollar[2].name {
 			case "reversed":
@@ -553,9 +594,9 @@ yydefault:
 			}
 			yyVAL.loopmods = yyDollar[1].loopmods
 		}
-	case 7:
+	case 11:
 		yyDollar = yyS[yypt-3 : yypt+1]
-		//line expressions.y:62
+		//line expressions.y:81
 		{ // TODO can this be a variable?
 			switch yyDollar[2].name {
 			case "limit":
@@ -575,65 +616,65 @@ yydefault:
 			}
 			yyVAL.loopmods = yyDollar[1].loopmods
 		}
-	case 8:
+	case 12:
 		yyDollar = yyS[yypt-1 : yypt+1]
-		//line expressions.y:84
+		//line expressions.y:103
 		{
 			val := yyDollar[1].val
 			yyVAL.f = func(_ Context) interface{} { return val }
 		}
-	case 9:
+	case 13:
 		yyDollar = yyS[yypt-1 : yypt+1]
-		//line expressions.y:85
+		//line expressions.y:104
 		{
 			name := yyDollar[1].name
 			yyVAL.f = func(ctx Context) interface{} { return ctx.Get(name) }
 		}
-	case 10:
+	case 14:
 		yyDollar = yyS[yypt-2 : yypt+1]
-		//line expressions.y:86
+		//line expressions.y:105
 		{
 			yyVAL.f = makeObjectPropertyExpr(yyDollar[1].f, yyDollar[2].name)
 		}
-	case 11:
+	case 15:
 		yyDollar = yyS[yypt-4 : yypt+1]
-		//line expressions.y:87
+		//line expressions.y:106
 		{
 			yyVAL.f = makeIndexExpr(yyDollar[1].f, yyDollar[3].f)
 		}
-	case 12:
+	case 16:
 		yyDollar = yyS[yypt-3 : yypt+1]
-		//line expressions.y:88
+		//line expressions.y:107
 		{
 			yyVAL.f = yyDollar[2].f
 		}
-	case 14:
+	case 18:
 		yyDollar = yyS[yypt-3 : yypt+1]
-		//line expressions.y:93
+		//line expressions.y:112
 		{
 			yyVAL.f = makeFilter(yyDollar[1].f, yyDollar[3].name, nil)
 		}
-	case 15:
+	case 19:
 		yyDollar = yyS[yypt-4 : yypt+1]
-		//line expressions.y:94
+		//line expressions.y:113
 		{
 			yyVAL.f = makeFilter(yyDollar[1].f, yyDollar[3].name, yyDollar[4].filter_params)
 		}
-	case 16:
+	case 20:
 		yyDollar = yyS[yypt-1 : yypt+1]
-		//line expressions.y:98
+		//line expressions.y:117
 		{
 			yyVAL.filter_params = []valueFn{yyDollar[1].f}
 		}
-	case 17:
+	case 21:
 		yyDollar = yyS[yypt-3 : yypt+1]
-		//line expressions.y:100
+		//line expressions.y:119
 		{
 			yyVAL.filter_params = append(yyDollar[1].filter_params, yyDollar[3].f)
 		}
-	case 19:
+	case 23:
 		yyDollar = yyS[yypt-3 : yypt+1]
-		//line expressions.y:104
+		//line expressions.y:123
 		{
 			fa, fb := yyDollar[1].f, yyDollar[3].f
 			yyVAL.f = func(ctx Context) interface{} {
@@ -641,9 +682,9 @@ yydefault:
 				return evaluator.Equal(a, b)
 			}
 		}
-	case 20:
+	case 24:
 		yyDollar = yyS[yypt-3 : yypt+1]
-		//line expressions.y:111
+		//line expressions.y:130
 		{
 			fa, fb := yyDollar[1].f, yyDollar[3].f
 			yyVAL.f = func(ctx Context) interface{} {
@@ -651,9 +692,9 @@ yydefault:
 				return !evaluator.Equal(a, b)
 			}
 		}
-	case 21:
+	case 25:
 		yyDollar = yyS[yypt-3 : yypt+1]
-		//line expressions.y:118
+		//line expressions.y:137
 		{
 			fa, fb := yyDollar[1].f, yyDollar[3].f
 			yyVAL.f = func(ctx Context) interface{} {
@@ -661,9 +702,9 @@ yydefault:
 				return evaluator.Less(b, a)
 			}
 		}
-	case 22:
+	case 26:
 		yyDollar = yyS[yypt-3 : yypt+1]
-		//line expressions.y:125
+		//line expressions.y:144
 		{
 			fa, fb := yyDollar[1].f, yyDollar[3].f
 			yyVAL.f = func(ctx Context) interface{} {
@@ -671,9 +712,9 @@ yydefault:
 				return evaluator.Less(a, b)
 			}
 		}
-	case 23:
+	case 27:
 		yyDollar = yyS[yypt-3 : yypt+1]
-		//line expressions.y:132
+		//line expressions.y:151
 		{
 			fa, fb := yyDollar[1].f, yyDollar[3].f
 			yyVAL.f = func(ctx Context) interface{} {
@@ -681,9 +722,9 @@ yydefault:
 				return evaluator.Less(b, a) || evaluator.Equal(a, b)
 			}
 		}
-	case 24:
+	case 28:
 		yyDollar = yyS[yypt-3 : yypt+1]
-		//line expressions.y:139
+		//line expressions.y:158
 		{
 			fa, fb := yyDollar[1].f, yyDollar[3].f
 			yyVAL.f = func(ctx Context) interface{} {
@@ -691,24 +732,24 @@ yydefault:
 				return evaluator.Less(a, b) || evaluator.Equal(a, b)
 			}
 		}
-	case 25:
+	case 29:
 		yyDollar = yyS[yypt-3 : yypt+1]
-		//line expressions.y:146
+		//line expressions.y:165
 		{
 			yyVAL.f = makeContainsExpr(yyDollar[1].f, yyDollar[3].f)
 		}
-	case 27:
+	case 31:
 		yyDollar = yyS[yypt-3 : yypt+1]
-		//line expressions.y:151
+		//line expressions.y:170
 		{
 			fa, fb := yyDollar[1].f, yyDollar[3].f
 			yyVAL.f = func(ctx Context) interface{} {
 				return evaluator.IsTrue(fa(ctx)) && evaluator.IsTrue(fb(ctx))
 			}
 		}
-	case 28:
+	case 32:
 		yyDollar = yyS[yypt-3 : yypt+1]
-		//line expressions.y:157
+		//line expressions.y:176
 		{
 			fa, fb := yyDollar[1].f, yyDollar[3].f
 			yyVAL.f = func(ctx Context) interface{} {

render/compiler_test.go

@@ -15,10 +15,10 @@ func addCompilerTestTags(s Config) {
 }
 
 var compilerErrorTests = []struct{ in, expected string }{
-	{"{% unknown_tag %}", "unknown tag"},
+	{`{% unknown_tag %}`, "unknown tag"},
 	{`{% block %}{% endblock %}`, "block compiler error"},
 	// {`{% tag %}`, "tag compiler error"},
-	// {"{%for syntax error%}{%endfor%}", "parse error"},
+	// {`{%for syntax error%}{%endfor%}`, "parse error"},
 }
 
 func TestCompileErrors(t *testing.T) {

tags/loop_tag.go

@@ -9,21 +9,54 @@ import (
 	"github.com/osteele/liquid/render"
 )
 
+const forloopVarName = "forloop"
+
 var errLoopContinueLoop = fmt.Errorf("continue outside a loop")
 var errLoopBreak = fmt.Errorf("break outside a loop")
 
-func breakTag(parameters string) (func(io.Writer, render.Context) error, error) {
+func breakTag(string) (func(io.Writer, render.Context) error, error) {
 	return func(_ io.Writer, ctx render.Context) error {
 		return ctx.WrapError(errLoopBreak)
 	}, nil
 }
 
-func continueTag(parameters string) (func(io.Writer, render.Context) error, error) {
+func continueTag(string) (func(io.Writer, render.Context) error, error) {
 	return func(_ io.Writer, ctx render.Context) error {
 		return ctx.WrapError(errLoopContinueLoop)
 	}, nil
 }
 
+func cycleTag(args string) (func(io.Writer, render.Context) error, error) {
+	return func(w io.Writer, ctx render.Context) error {
+		expr, err := expression.Parse("{%cycle " + args)
+		if err != nil {
+			return err
+		}
+		value, err := ctx.Evaluate(expr)
+		if err != nil {
+			return err
+		}
+		array := value.([]interface{})
+		if len(array) == 0 {
+			return nil
+		}
+		loopVar := ctx.Get(forloopVarName)
+		if loopVar == nil {
+			return ctx.Errorf("cycle must be within a forloop")
+		}
+		// the next few lines could panic if the user spoofs us by creating their own loop object
+		// “C++ protects against accident, not against fraud.” – Bjarne Stroustrup
+		loopRec := loopVar.(map[string]interface{})
+		cycleMap := loopRec[".cycles"].(map[string]int)
+		group := ""
+		n := cycleMap[group]
+		cycleMap[group] = n + 1
+		fmt.Println(cycleMap)
+		_, err = w.Write([]byte(fmt.Sprint(array[n%len(array)])))
+		return err
+	}, nil
+}
+
 func parseLoopExpression(source string) (expression.Expression, error) {
 	expr, err := expression.Parse("%loop " + source)
 	if err != nil {
@@ -69,11 +102,11 @@ func loopTagParser(node render.BlockNode) (func(io.Writer, render.Context) error
 				length = rt.Len()
 			}
 		}
-		const forloopName = "forloop"
 		defer func(index, forloop interface{}) {
-			ctx.Set(forloopName, index)
+			ctx.Set(forloopVarName, index)
 			ctx.Set(loop.Variable, forloop)
-		}(ctx.Get(forloopName), ctx.Get(loop.Variable))
+		}(ctx.Get(forloopVarName), ctx.Get(loop.Variable))
+		cycleMap := map[string]int{}
 	loop:
 		for i := 0; i < length; i++ {
 			j := i
@@ -81,7 +114,7 @@ func loopTagParser(node render.BlockNode) (func(io.Writer, render.Context) error
 				j = rt.Len() - 1 - i
 			}
 			ctx.Set(loop.Variable, rt.Index(j).Interface())
-			ctx.Set(forloopName, map[string]interface{}{
+			ctx.Set(forloopVarName, map[string]interface{}{
 				"first":   i == 0,
 				"last":    i == length-1,
 				"index":   i + 1,
@@ -89,6 +122,7 @@ func loopTagParser(node render.BlockNode) (func(io.Writer, render.Context) error
 				"rindex":  length - i,
 				"rindex0": length - i - 1,
 				"length":  length,
+				".cycles": cycleMap,
 			})
 			err := ctx.RenderChildren(w)
 			switch {

tags/loop_tag_test.go

@@ -55,7 +55,11 @@ var loopTests = []struct{ in, expected string }{
 	{`{% for a in array %}{% if a == 'second' %}{% break %}{% endif %}{{ a }}{% endfor %}`, "first"},
 	{`{% for a in array %}{% if a == 'second' %}{% continue %}{% endif %}{{ a }}.{% endfor %}`, "first.third."},
 
+	// hash
 	{`{% for a in hash %}{{ a }}{% endfor %}`, "a"},
+
+	// cycle
+	{`{% for a in array %}{% cycle 'even', 'odd' %}.{% endfor %}`, "even.odd.even."},
 }
 
 var loopErrorTests = []struct{ in, expected string }{

tags/standard_tags.go

@@ -19,6 +19,7 @@ func AddStandardTags(c render.Config) {
 	// but it ignores any syntax specified here.
 	c.AddTag("break", breakTag)
 	c.AddTag("continue", continueTag)
+	c.AddTag("cycle", cycleTag)
 	c.AddBlock("capture").Compiler(captureTagParser)
 	c.AddBlock("case").Clause("when").Clause("else").Compiler(caseTagParser)
 	c.AddBlock("comment")