Use % for context instead of @

src/template/lib.zig

@@ -3,7 +3,7 @@ const std = @import("std");
 pub fn main() !void {
     try execute(
         std.io.getStdOut().writer(),
-        .{ .test_tmpl = "{.x} {@context_foo}" },
+        .{ .test_tmpl = "{.x} {%context_foo}" },
         @embedFile("./test.tmp.html"),
         .{
             .community = .{ .name = "abcd" },
@@ -15,6 +15,9 @@ pub fn main() !void {
             .bar = .{ .x = "x" },
             .qux = false,
             .quxx = true,
+            .maybe_foo = @as(?[]const u8, "foo"),
+            .maybe_bar = @as(?[]const u8, null),
+            .x = "y",
         },
         .{
             .context_foo = "foo",
@@ -83,9 +86,33 @@ fn executeStatement(
         .@"if" => |if_stmt| {
             const condition = evaluateExpression(if_stmt.header.condition, args, captures, context);
             const subtemplate = if_stmt.subtemplate;
-            if (condition) {
+            var was_true: bool = false;
-                try executeTemplate(writer, templates, subtemplate, args, captures, context);
+            if (if_stmt.header.capture) |capture| {
+                if (condition) |val| {
+                    was_true = true;
+                    try executeTemplate(
+                        writer,
+                        templates,
+                        subtemplate,
+                        args,
+                        addCapture(captures, capture, val),
+                        context,
+                    );
+                }
             } else {
+                if (condition) {
+                    was_true = true;
+                    try executeTemplate(
+                        writer,
+                        templates,
+                        subtemplate,
+                        args,
+                        captures,
+                        context,
+                    );
+                }
+            }
+            if (!was_true) {
                 if (if_stmt.else_branch) |branch| switch (branch) {
                     .@"else" => |subtmpl| try executeTemplate(writer, templates, subtmpl, args, captures, context),
                     .elif => |elif| try executeStatement(writer, templates, .{ .@"if" = elif.* }, args, captures, context),
@@ -158,6 +185,7 @@ fn evaluateExpression(
 }
 
 fn AddCapture(comptime Root: type, comptime name: []const u8, comptime Val: type) type {
+    if (std.mem.eql(u8, name, "_")) return Root;
     var fields = std.meta.fields(Root) ++ [_]std.builtin.Type.StructField{.{
         .name = name,
         .field_type = Val,
@@ -175,6 +203,7 @@ fn AddCapture(comptime Root: type, comptime name: []const u8, comptime Val: type
 }
 
 fn addCapture(root: anytype, comptime name: []const u8, val: anytype) AddCapture(@TypeOf(root), name, @TypeOf(val)) {
+    if (comptime std.mem.eql(u8, name, "_")) return root;
     var result = std.mem.zeroInit(AddCapture(@TypeOf(root), name, @TypeOf(val)), root);
     @field(result, name) = val;
     return result;
@@ -359,6 +388,8 @@ fn parseTemplateTokens(comptime tokens: ControlTokenIter) []const TemplateToken
             .slash => items = items ++ [_]TemplateToken{.{ .text = "/" }},
             .equals => items = items ++ [_]TemplateToken{.{ .text = "=" }},
             .at => items = items ++ [_]TemplateToken{.{ .text = "@" }},
+            .comma => items = items ++ [_]TemplateToken{.{ .text = "," }},
+            .percent => items = items ++ [_]TemplateToken{.{ .text = "%" }},
         };
 
         return items;
@@ -381,7 +412,7 @@ fn parseExpression(comptime tokens: ControlTokenIter) ParseResult(ControlTokenIt
                 iter = names.new_iter;
                 break .{ .capture_deref = names.item };
             },
-            .at => {
+            .percent => {
                 const names = parseDeref(iter);
                 iter = names.new_iter;
                 break .{ .context_deref = names.item };
@@ -455,7 +486,7 @@ fn parseControlBlock(comptime tokens: ControlTokenIter) ParseResult(ControlToken
                     .@"if" => break .{ .end_if = {} },
                 }
             },
-            .period, .dollar, .at => {
+            .period, .dollar, .percent => {
                 iter.putBack(token);
                 const expr = parseExpression(iter);
                 iter = expr.new_iter;
@@ -551,15 +582,61 @@ fn parseForHeader(comptime tokens: ControlTokenIter) ParseResult(ControlTokenIte
     }
 }
 
+fn tryParseCapture(comptime tokens: ControlTokenIter) ?ParseResult(ControlTokenIter, []const []const u8) {
+    comptime {
+        var iter = tokens;
+
+        iter = skipWhitespace(iter);
+        if ((iter.next() orelse return null) != .pipe) return null;
+        var captures: []const []const u8 = &.{};
+        while (true) {
+            iter = skipWhitespace(iter);
+            if ((iter.next() orelse return null) != .dollar) return null;
+            iter = skipWhitespace(iter);
+            const name = switch (iter.next() orelse return null) {
+                .text => |text| text,
+                else => return null,
+            };
+            iter = skipWhitespace(iter);
+            captures = captures ++ &[_][]const u8{name};
+
+            switch (iter.next() orelse return null) {
+                .pipe => break,
+                .comma => {},
+                else => return null,
+            }
+        }
+
+        return .{
+            .new_iter = iter,
+            .item = captures,
+        };
+    }
+}
+
 fn parseIfHeader(comptime tokens: ControlTokenIter) ParseResult(ControlTokenIter, IfHeader) {
     comptime {
         const condition = parseExpression(tokens);
         var iter = condition.new_iter;
 
+        const captures = tryParseCapture(iter);
+        if (captures) |cap| {
+            if (cap.item.len == 1) {
+                return .{
+                    .new_iter = cap.new_iter,
+                    .item = IfHeader{
+                        .condition = condition.item,
+                        .capture = cap.item[0],
+                    },
+                };
+            } else @compileError("Only one capture allowed for if statements");
+        }
+
         return .{
             .new_iter = iter,
             .item = .{
                 .condition = condition.item,
+                .capture = null,
             },
         };
     }
@@ -582,7 +659,7 @@ fn parseDeref(comptime tokens: ControlTokenIter) ParseResult(ControlTokenIter, [
                     if (wants != .period) @compileError("Unexpected token \".\"");
                     wants = .text;
                 },
-                else => if (wants == .period) return .{
+                else => if (wants == .period or fields.len == 0) return .{
                     .new_iter = iter,
                     .item = fields,
                 } else @compileError("Unexpected token"),
@@ -657,6 +734,7 @@ const CallTemplate = struct {
 
 const IfHeader = struct {
     condition: Expression,
+    capture: ?[]const u8,
 };
 
 const Statement = union(enum) {
@@ -707,6 +785,8 @@ const ControlToken = union(enum) {
     slash: void,
     equals: void,
     at: void,
+    comma: void,
+    percent: void,
 };
 
 const ControlTokenIter = struct {
@@ -737,6 +817,8 @@ const ControlTokenIter = struct {
             '/' => return .{ .slash = {} },
             '=' => return .{ .equals = {} },
             '@' => return .{ .at = {} },
+            ',' => return .{ .comma = {} },
+            '%' => return .{ .percent = {} },
             ' ', '\t', '\n', '\r' => {
                 var idx: usize = 0;
                 while (idx < remaining.len and std.mem.indexOfScalar(u8, " \t\n\r", remaining[idx]) != null) : (idx += 1) {}

src/template/test.tmp.html

@@ -22,9 +22,14 @@
         neither
       {=/if}
 
-      <template>{#template test_tmpl .bar}</template>
+      {#if .maybe_foo |$v|}{$v}{#else}null{/if}
+      {#if .maybe_bar |$v|}{$v}{#else}null{/if}
+      {#if .maybe_foo |$_|}abcd{#else}null{/if}
 
-      {@context_foo}
+      <template>{#template test_tmpl .bar}</template>
+      <template>{#template test_tmpl .}</template>
+
+      {%context_foo}
     </section>
   </body>
 </html>