Implement loop reversed

README.md

@@ -21,7 +21,10 @@
     - [ ] case/when
   - [ ] Iteration
         - [x] for
-            - [ ] limit, offset, range, reversed
+            - [ ] limit
+            - [ ] offset
+            - [ ] range
+            - [x] reversed
         - [ ] break, continue
         - [ ] loop variables
         - [ ] tablerow

expressions/context.go

@@ -25,9 +25,3 @@ func (c *context) Get(name string) interface{} {
 func (c *context) Set(name string, value interface{}) {
 	c.vars[name] = value
 }
-
-// Loop describes the result of parsing and then evaluating a loop statement.
-type Loop struct {
-	Name string
-	Expr interface{}
-}

expressions/evaluator.go

@@ -1,41 +1,5 @@
 package expressions
 
-import (
-	"fmt"
-
-	"github.com/osteele/liquid/errors"
-)
-
-// Expression is a parsed expression.
-type Expression interface {
-	// Evaluate evaluates an expression in a context.
-	Evaluate(ctx Context) (interface{}, error)
-}
-
-type expression struct {
-	evaluator func(Context) interface{}
-}
-
-// Parse parses an expression string into an Expression.
-func Parse(source string) (expr Expression, err error) {
-	defer func() {
-		if r := recover(); r != nil {
-			switch e := r.(type) {
-			case errors.UndefinedFilter:
-				err = e
-			default:
-				panic(r)
-			}
-		}
-	}()
-	lexer := newLexer([]byte(source + ";"))
-	n := yyParse(lexer)
-	if n != 0 {
-		return nil, fmt.Errorf("parse error in %s", source)
-	}
-	return &expression{lexer.val}, nil
-}
-
 func (e expression) Evaluate(ctx Context) (interface{}, error) {
 	return e.evaluator(ctx), nil
 }

expressions/expressions.y

@@ -17,8 +17,10 @@ func init() {
    name string
    val interface{}
    f func(Context) interface{}
+   loopmods LoopModifiers
 }
 %type <f> expr rel expr1 loop
+%type<loopmods> loop_modifiers
 %token <val> LITERAL
 %token <name> IDENTIFIER KEYWORD RELATION
 %token ASSIGN LOOP
@@ -38,14 +40,24 @@ start:
 | LOOP loop { yylex.(*lexer).val = $2 }
 ;
 
-loop: IDENTIFIER IN expr1 ';' {
-	name, expr := $1, $3
+loop: IDENTIFIER IN expr1 loop_modifiers ';' {
+	name, expr, mods := $1, $3, $4
 	$$ = func(ctx Context) interface{} {
-		return &Loop{name, expr(ctx)}
+		return &Loop{name, expr(ctx), mods}
 	}
 }
 ;
 
+loop_modifiers: /* empty */ { $$ = LoopModifiers{} }
+| loop_modifiers IDENTIFIER {
+	if $2 != "reversed" {
+		panic(ParseError(fmt.Sprintf("undefined loop modifier: %s", $2)))
+	}
+	$1.Reversed = true
+	$$ = $1
+}
+;
+
 expr:
   LITERAL { val := $1; $$ = func(_ Context) interface{} { return val } }
 | IDENTIFIER { name := $1; $$ = func(ctx Context) interface{} { return ctx.Get(name) } }

expressions/parser.go

@@ -0,0 +1,54 @@
+package expressions
+
+import (
+	"fmt"
+
+	"github.com/osteele/liquid/errors"
+)
+
+// Loop describes the result of parsing and then evaluating a loop statement.
+type Loop struct {
+	Name string
+	Expr interface{}
+	LoopModifiers
+}
+
+type LoopModifiers struct {
+	Reversed bool
+}
+
+type ParseError string
+
+func (e ParseError) Error() string { return string(e) }
+
+// Expression is a parsed expression.
+type Expression interface {
+	// Evaluate evaluates an expression in a context.
+	Evaluate(ctx Context) (interface{}, error)
+}
+
+type expression struct {
+	evaluator func(Context) interface{}
+}
+
+// Parse parses an expression string into an Expression.
+func Parse(source string) (expr Expression, err error) {
+	defer func() {
+		if r := recover(); r != nil {
+			switch e := r.(type) {
+			case ParseError:
+				err = e
+			case errors.UndefinedFilter:
+				err = e
+			default:
+				panic(r)
+			}
+		}
+	}()
+	lexer := newLexer([]byte(source + ";"))
+	n := yyParse(lexer)
+	if n != 0 {
+		return nil, fmt.Errorf("parse error in %s", source)
+	}
+	return &expression{lexer.val}, nil
+}

expressions/y.go

@@ -18,10 +18,11 @@ func init() {
 
 //line expressions.y:16
 type yySymType struct {
-	yys  int
-	name string
-	val  interface{}
-	f    func(Context) interface{}
+	yys      int
+	name     string
+	val      interface{}
+	f        func(Context) interface{}
+	loopmods LoopModifiers
 }
 
 const LITERAL = 57346
@@ -71,50 +72,50 @@ var yyExca = [...]int{
 
 const yyPrivate = 57344
 
-const yyLast = 42
+const yyLast = 43
 
 var yyAct = [...]int{
 
 	29, 6, 16, 14, 5, 14, 14, 17, 18, 15,
-	32, 15, 15, 19, 9, 13, 24, 25, 26, 27,
-	20, 21, 22, 31, 28, 30, 13, 13, 23, 34,
-	33, 7, 8, 7, 8, 3, 4, 12, 10, 1,
-	11, 2,
+	32, 15, 15, 19, 36, 9, 24, 25, 26, 27,
+	13, 23, 20, 31, 28, 30, 35, 13, 7, 8,
+	33, 12, 3, 4, 21, 22, 7, 8, 10, 1,
+	34, 11, 2,
 }
 var yyPact = [...]int{
 
-	27, -1000, -3, 33, 32, 1, -8, -1000, -1000, -1000,
-	-5, -1000, 8, 16, 23, 29, 29, 29, 29, 29,
-	29, -1000, 29, -1000, -10, -7, -7, -7, 13, -7,
-	12, -7, -1000, -1000, -1000,
+	24, -1000, -2, 33, 26, 6, -8, -1000, -1000, -1000,
+	-5, -1000, 10, 29, 16, 32, 32, 32, 32, 32,
+	32, -1000, 32, -1000, -10, -7, -7, -7, 13, -7,
+	6, -7, -1000, -1000, 9, -1000, -1000,
 }
 var yyPgo = [...]int{
 
-	0, 0, 41, 4, 40, 39,
+	0, 0, 42, 4, 41, 40, 39,
 }
 var yyR1 = [...]int{
 
-	0, 5, 5, 5, 4, 1, 1, 1, 1, 3,
-	3, 3, 2, 2, 2, 2,
+	0, 6, 6, 6, 4, 5, 5, 1, 1, 1,
+	1, 3, 3, 3, 2, 2, 2, 2,
 }
 var yyR2 = [...]int{
 
-	0, 2, 5, 2, 4, 1, 1, 3, 4, 1,
-	3, 4, 1, 3, 3, 3,
+	0, 2, 5, 2, 5, 0, 2, 1, 1, 3,
+	4, 1, 3, 4, 1, 3, 3, 3,
 }
 var yyChk = [...]int{
 
-	-1000, -5, -2, 8, 9, -3, -1, 4, 5, 17,
+	-1000, -6, -2, 8, 9, -3, -1, 4, 5, 17,
 	5, -4, 5, 14, 13, 19, 10, 15, 16, 18,
 	12, 5, 6, 5, -1, -1, -1, -1, -3, -1,
-	-3, -1, 20, 17, 17,
+	-3, -1, 20, 17, -5, 17, 5,
 }
 var yyDef = [...]int{
 
-	0, -2, 0, 0, 0, 12, 9, 5, 6, 1,
+	0, -2, 0, 0, 0, 14, 11, 7, 8, 1,
 	0, 3, 0, 0, 0, 0, 0, 0, 0, 0,
-	0, 10, 0, 7, 0, 13, 14, 15, 0, 9,
-	0, 11, 8, 2, 4,
+	0, 12, 0, 9, 0, 15, 16, 17, 0, 11,
+	5, 13, 10, 2, 0, 4, 6,
 }
 var yyTok1 = [...]int{
 
@@ -480,13 +481,13 @@ yydefault:
 
 	case 1:
 		yyDollar = yyS[yypt-2 : yypt+1]
-		//line expressions.y:30
+		//line expressions.y:32
 		{
 			yylex.(*lexer).val = yyDollar[1].f
 		}
 	case 2:
 		yyDollar = yyS[yypt-5 : yypt+1]
-		//line expressions.y:31
+		//line expressions.y:33
 		{
 			name, expr := yyDollar[2].name, yyDollar[4].f
 			yylex.(*lexer).val = func(ctx Context) interface{} {
@@ -496,36 +497,52 @@ yydefault:
 		}
 	case 3:
 		yyDollar = yyS[yypt-2 : yypt+1]
-		//line expressions.y:38
+		//line expressions.y:40
 		{
 			yylex.(*lexer).val = yyDollar[2].f
 		}
 	case 4:
-		yyDollar = yyS[yypt-4 : yypt+1]
-		//line expressions.y:41
+		yyDollar = yyS[yypt-5 : yypt+1]
+		//line expressions.y:43
 		{
-			name, expr := yyDollar[1].name, yyDollar[3].f
+			name, expr, mods := yyDollar[1].name, yyDollar[3].f, yyDollar[4].loopmods
 			yyVAL.f = func(ctx Context) interface{} {
-				return &Loop{name, expr(ctx)}
+				return &Loop{name, expr(ctx), mods}
 			}
 		}
 	case 5:
+		yyDollar = yyS[yypt-0 : yypt+1]
+		//line expressions.y:51
+		{
+			yyVAL.loopmods = LoopModifiers{}
+		}
+	case 6:
+		yyDollar = yyS[yypt-2 : yypt+1]
+		//line expressions.y:52
+		{
+			if yyDollar[2].name != "reversed" {
+				panic(ParseError(fmt.Sprintf("undefined loop modifier: %s", yyDollar[2].name)))
+			}
+			yyDollar[1].loopmods.Reversed = true
+			yyVAL.loopmods = yyDollar[1].loopmods
+		}
+	case 7:
 		yyDollar = yyS[yypt-1 : yypt+1]
-		//line expressions.y:50
+		//line expressions.y:62
 		{
 			val := yyDollar[1].val
 			yyVAL.f = func(_ Context) interface{} { return val }
 		}
-	case 6:
+	case 8:
 		yyDollar = yyS[yypt-1 : yypt+1]
-		//line expressions.y:51
+		//line expressions.y:63
 		{
 			name := yyDollar[1].name
 			yyVAL.f = func(ctx Context) interface{} { return ctx.Get(name) }
 		}
-	case 7:
+	case 9:
 		yyDollar = yyS[yypt-3 : yypt+1]
-		//line expressions.y:52
+		//line expressions.y:64
 		{
 			e, attr := yyDollar[1].f, yyDollar[3].name
 			yyVAL.f = func(ctx Context) interface{} {
@@ -541,9 +558,9 @@ yydefault:
 				return nil
 			}
 		}
-	case 8:
+	case 10:
 		yyDollar = yyS[yypt-4 : yypt+1]
-		//line expressions.y:67
+		//line expressions.y:79
 		{
 			e, i := yyDollar[1].f, yyDollar[3].f
 			yyVAL.f = func(ctx Context) interface{} {
@@ -562,21 +579,21 @@ yydefault:
 				return nil
 			}
 		}
-	case 10:
+	case 12:
 		yyDollar = yyS[yypt-3 : yypt+1]
-		//line expressions.y:88
+		//line expressions.y:100
 		{
 			yyVAL.f = makeFilter(yyDollar[1].f, yyDollar[3].name, nil)
 		}
-	case 11:
+	case 13:
 		yyDollar = yyS[yypt-4 : yypt+1]
-		//line expressions.y:89
+		//line expressions.y:101
 		{
 			yyVAL.f = makeFilter(yyDollar[1].f, yyDollar[3].name, yyDollar[4].f)
 		}
-	case 13:
+	case 15:
 		yyDollar = yyS[yypt-3 : yypt+1]
-		//line expressions.y:94
+		//line expressions.y:106
 		{
 			fa, fb := yyDollar[1].f, yyDollar[3].f
 			yyVAL.f = func(ctx Context) interface{} {
@@ -584,9 +601,9 @@ yydefault:
 				return generics.Equal(a, b)
 			}
 		}
-	case 14:
+	case 16:
 		yyDollar = yyS[yypt-3 : yypt+1]
-		//line expressions.y:101
+		//line expressions.y:113
 		{
 			fa, fb := yyDollar[1].f, yyDollar[3].f
 			yyVAL.f = func(ctx Context) interface{} {
@@ -594,9 +611,9 @@ yydefault:
 				return generics.Less(a, b)
 			}
 		}
-	case 15:
+	case 17:
 		yyDollar = yyS[yypt-3 : yypt+1]
-		//line expressions.y:108
+		//line expressions.y:120
 		{
 			fa, fb := yyDollar[1].f, yyDollar[3].f
 			yyVAL.f = func(ctx Context) interface{} {

tags/loop.go

@@ -32,7 +32,11 @@ func loopTag(node chunks.ASTControlTag) func(io.Writer, chunks.Context) error {
 			return nil
 		}
 		for i := 0; i < rt.Len(); i++ {
-			ctx.Set(loop.Name, rt.Index(i).Interface())
+			j := i
+			if loop.Reversed {
+				j = rt.Len() - 1 - i
+			}
+			ctx.Set(loop.Name, rt.Index(j).Interface())
 			err := ctx.RenderASTSequence(w, node.Body)
 			if err != nil {
 				return err

tags/tags_test.go

@@ -12,7 +12,9 @@ import (
 var parseErrorTests = []struct{ in, expected string }{
 	{"{%unknown_tag%}", "unknown tag"},
 	{"{%if syntax error%}", "unterminated if tag"},
+	// TODO once expression parsing is moved to template parse stage
 	// {"{%if syntax error%}{%endif%}", "parse error"},
+	// {"{%for a in ar unknown%}{{a}} {%endfor%}", "TODO"},
 }
 
 var tagTests = []struct{ in, expected string }{
@@ -45,6 +47,7 @@ var tagTests = []struct{ in, expected string }{
 	{"{%assign av = obj.a%}{{av}}", "1"},
 
 	{"{%for a in ar%}{{a}} {%endfor%}", "first second third "},
+	{"{%for a in ar reversed%}{{a}} {%endfor%}", "third second first "},
 }
 
 var tagTestContext = chunks.NewContext(map[string]interface{}{