Split up template parsing and execution

src/template/lib.zig

@@ -4,63 +4,141 @@ pub fn main() !void {
     try execute(std.io.getStdOut().writer(), @embedFile("./test.tmp.html"), .{ .community = .{ .name = "abcd" } });
 }
 
+const logging = false;
+
 pub fn execute(writer: anytype, comptime template: []const u8, args: anytype) !void {
     @setEvalBranchQuota(@intCast(u32, template.len * 6));
     comptime var iter = TokenIter{ .text = template };
-    comptime var state: State = .text;
     inline while (comptime iter.next()) |token| {
+        if (logging) @compileLog(token);
         switch (token) {
-            .text => |text| switch (state) {
+            .text => |text| try writer.writeAll(text),
-                .text => try writer.writeAll(text),
+            .open_bracket => {
-                else => @compileError("Text token not allowed in state " ++ @tagName(state) ++ text),
+                const next = comptime iter.peek() orelse @compileError("Unexpected end of template");
-            },
+                if (next == .open_bracket) {
-            .open_bracket => switch (state) {
-                .text => state = .template_start,
-                .template_start => {
                     try writer.writeByte('{');
-                    state = .text;
+                    _ = comptime iter.next();
-                },
+                } else {
-                else => @compileError(""),
+                    const result = comptime parseStatement(iter);
+                    try executeStatement(writer, result.statement, args);
+                    iter = result.new_iter;
+                }
             },
-            .close_bracket => switch (state) {
+            .close_bracket => {
-                .text => state = .text_close_bracket,
+                const next = comptime iter.next() orelse @compileError("Unexpected end of template");
-                .text_close_bracket => {
+                if (comptime next == .close_bracket) try writer.writeByte('}') else @compileError("Unpaired close bracket, did you mean \"}}\"?");
-                    try writer.writeByte('}');
-                    state = .text;
-                },
-                .template_start, .template => state = .text,
-                //else => @compileError(""),
-            },
-            .whitespace => |wsp| switch (state) {
-                .text => try writer.writeAll(wsp),
-                else => {},
-            },
-            .period => switch (state) {
-                .text => try writer.writeByte('.'),
-                .template_start, .template => {
-                    try argDeref(writer, &iter, args);
-                    state = .template;
-                },
-                else => @compileError(""),
             },
+            .whitespace => |wsp| try writer.writeAll(wsp),
+            .period => try writer.writeByte('.'),
+            .pound => try writer.writeByte('#'),
         }
     }
 }
 
-fn argDeref(writer: anytype, comptime iter: *TokenIter, arg: anytype) !void {
+fn executeStatement(writer: anytype, comptime stmt: Statement, args: anytype) !void {
-    inline while (comptime iter.peek()) |token| {
+    switch (stmt) {
-        switch (token) {
+        .expression => |expr| switch (expr) {
-            .period => {},
+            .arg_deref => |fields| try argDeref(writer, fields, args),
-            .text => |text| {
+        },
-                _ = comptime iter.next();
+        else => @compileError("TODO"),
-                return argDeref(writer, iter, @field(arg, text));
-            },
-            else => return try writer.writeAll(arg),
-        }
-        _ = comptime iter.next();
     }
 }
 
+fn argDeref(writer: anytype, comptime names: []const []const u8, arg: anytype) !void {
+    if (names.len == 0) {
+        const T = @TypeOf(arg);
+        if (comptime std.meta.trait.isZigString(T)) return writer.writeAll(arg);
+        return std.fmt.format(writer, "{any}", .{arg});
+    }
+
+    return argDeref(writer, names[1..], @field(arg, names[0]));
+}
+
+fn parseStatement(comptime tokens: TokenIter) StatementResult {
+    comptime {
+        var iter = tokens;
+        while (iter.next()) |token| switch (token) {
+            .whitespace => {},
+            .pound => {
+                const next = iter.next() orelse @compileError("Unexpected end of template");
+                if (logging) @compileLog("keyword", next);
+                if (next != .text) @compileError("Expected keyword following '#' character");
+                const text = next.text;
+                const keyword = std.meta.stringToEnum(Keyword, text) orelse @compileError("Unknown keyword: " ++ text);
+
+                _ = keyword;
+                @panic("todo");
+            },
+            .period => {
+                const expr = parseArgDeref(iter);
+                iter = expr.new_iter;
+                while (iter.next()) |it| switch (it) {
+                    .whitespace => {},
+                    .close_bracket => break,
+                    else => @compileError("TODO"),
+                };
+                return .{ .new_iter = iter, .statement = .{
+                    .expression = expr.expression,
+                } };
+            },
+            else => @compileError(""),
+        };
+
+        @compileError("Unexpected end of template");
+    }
+}
+
+fn parseArgDeref(comptime tokens: TokenIter) ExpressionResult {
+    comptime {
+        var iter = tokens;
+        var fields: []const []const u8 = &.{};
+        var wants = .text;
+        while (iter.peek()) |token| {
+            switch (token) {
+                .whitespace => {},
+                .text => |text| {
+                    if (wants != .text) @compileError("Unexpected token \"" ++ text ++ "\"");
+                    fields = fields ++ [1][]const u8{text};
+                    wants = .period;
+                },
+                .period => {
+                    if (wants != .period) @compileError("Unexpected token \".\"");
+                    wants = .text;
+                },
+                else => if (wants == .period) return .{
+                    .new_iter = iter,
+                    .expression = .{ .arg_deref = fields },
+                } else @compileError("Unexpected token"),
+            }
+            _ = iter.next();
+        }
+    }
+}
+
+const Expression = union(enum) {
+    arg_deref: []const []const u8,
+};
+
+const ExpressionResult = struct {
+    new_iter: TokenIter,
+    expression: Expression,
+};
+
+const Statement = union(enum) {
+    expression: Expression,
+    for_loop: struct {
+        subtemplate: []const u8,
+        indexable: Expression,
+        iteration_capture: []const u8,
+        index_capture: ?[]const u8,
+    },
+};
+
+const StatementResult = struct {
+    new_iter: TokenIter,
+    statement: Statement,
+};
+
 const State = enum {
     text,
     text_close_bracket,
@@ -68,12 +146,17 @@ const State = enum {
     template,
 };
 
+const Keyword = enum {
+    @"for",
+};
+
 const Token = union(enum) {
     text: []const u8,
     open_bracket: void,
     close_bracket: void,
     period: void,
     whitespace: []const u8,
+    pound: void,
 };
 
 const TokenIter = struct {
@@ -96,6 +179,7 @@ const TokenIter = struct {
             '{' => return .{ .open_bracket = {} },
             '}' => return .{ .close_bracket = {} },
             '.' => return .{ .period = {} },
+            '#' => return .{ .pound = {} },
             ' ', '\t', '\n', '\r' => {
                 var idx: usize = 0;
                 while (idx < remaining.len and std.mem.indexOfScalar(u8, " \t\n\r", remaining[idx]) != null) : (idx += 1) {}
@@ -105,7 +189,7 @@ const TokenIter = struct {
             },
             else => {
                 var idx: usize = 0;
-                while (idx < remaining.len and std.mem.indexOfScalar(u8, "{}. \t\n\r", remaining[idx]) == null) : (idx += 1) {}
+                while (idx < remaining.len and std.mem.indexOfScalar(u8, "{}.# \t\n\r", remaining[idx]) == null) : (idx += 1) {}
 
                 self.start += idx - 1;
                 return .{ .text = remaining[0..idx] };

src/template/test.tmp.html

@@ -1,7 +1,7 @@
 <!DOCTYPE html>
 <html>
   <head>
-    <title>{ .community.name }</title>
+    <title>{.community.name}</title>
   </head>
 
   <body>
@@ -9,10 +9,11 @@
     <h2> {{ REAL BRACKETS }} </h2>
 
     <section>
+      {{#for .community}}
       {{#for args.notes |$note, $i|}}
         <h3>Note no. {{$i}}</h3>
         {{#template note_display ($note)}}
-      {{/for}}
+      {{#end}}
     </section>
   </body>
 </html>