kevsmith / herml Goto Github PK

Hi, nice stuff!

However I noticed that it fails to parse some common hamls:

%h1 Some title

or

%p
nice
%span Chicken Fried

The Leex is included in Erlang R13B01 does not work with outdir option.

To make Herml work for this Erlang version, Makefile should be changed to:
leex:file("src/herml_scan.xrl")

I've found Herml (tested on 2942bd1) to hang in parser-generated code on the following template:

!!!
%html
  %head
    %meta[{charset,"utf-8"}]/

Generated parser continued to recursively call itself herml_scan:string/4 in an endless loop, quickly hogging all memory. Unfortunately, I'm too newbie to Erlang and leex, so I don't really understand why this happens. Anyway, the calls are occurring in this way:

...
string/4(",\"utf-8\"}]/", 1, ",\"utf-8\"}]/", [{chr,1,"charset"},{lcurly,1,[123]},{lbrace,1,[91]},{chr,1,[109,101,116,97]},{tag_start,1,[37]}])
string/4("\"utf-8\"}]/", 1, "\"utf-8\"}]/", [{comma,1,[44]},{chr,1,"charset"},{lcurly,1,[123]},{lbrace,1,[91]},{chr,1,[109,101,116,97]},{tag_start,1,[37]}])
string/4("\"utf-8\"}]/", 1, "\"utf-8\"}]/", [{pipe,1,[]},{comma,1,[44]},{chr,1,"charset"},{lcurly,1,[123]},{lbrace,1,[91]},{chr,1,[109,101,116,97]},{tag_start,1,[37]}])
string/4("\"utf-8\"}]/", 1, "\"utf-8\"}]/", [{pipe,1,[]},{pipe,1,[]},{comma,1,[44]},{chr,1,"charset"},{lcurly,1,[123]},{lbrace,1,[91]},{chr,1,[109,101,116,97]},{tag_start,1,[37]}])
string/4("\"utf-8\"}]/", 1, "\"utf-8\"}]/", [{pipe,1,[]},{pipe,1,[]},{pipe,1,[]},{comma,1,[44]},{chr,1,"charset"},{lcurly,1,[123]},{lbrace,1,[91]},{chr,1,[109,101,116,97]},{tag_start,1,[37]}])
string/4("\"utf-8\"}]/", 1, "\"utf-8\"}]/", [{pipe,1,[]},{pipe,1,[]},{pipe,1,[]},{pipe,1,[]},{comma,1,[44]},{chr,1,"charset"},{lcurly,1,[123]},{lbrace,1,[91]},{chr,1,[109,101,116,97]},{tag_start,1,[37]}])
...

There are certainly no "|" characters in template, and I really don't know why {pipe,1,[]} is there.

After some mindless fiddling, I've found that similiar hangs happen on intentionally malformed %meta[{charset,"utf-8}]/ (missing second double quote) code, and when there are any "unknown" characters (for example, UTF-8 Cyrillic).

I've attempted to fix the issue with drdaeman/herml@58b4958, but due to a lack of expertise I don't know whenever this is the proper solution, or it just happen to work.

Although it spawns processes, I doubt that herml_manager may be a bottle neck.

I propose that a template be compiled to a module in-memory (the module name can be referred from the template path implicitly, or specified explicitly) with a function "render" so that it can render itself.

In other words, a template is converted into code instead of data. This way, the Erlang VM caches and manages the templates for us efficiently. When we want to render, just call it. When we want to update a template, just recompile it and the Erlang VM will automatically replace the old code with the new one for us.

For example, the library "erlang-gettext" can compile a plain text .po file to a module elegantly like this:
http://github.com/davide/erlang-gettext/blob/baee1560a705d1337fa05be822fde57abef1d312/src/gettext_generate.erl

For a feeling, ErlyDTL is working like this:
erlydtl:compile("/path/to/welcome.html", welcome_template),
welcome_template:render([
{name, "Johnny"},
{friends, [<<"Frankie Lee">>, <<"Judas Priest">>]},
{primes, [1, 2, "3", <<"5">>]}
]).

I'm new to AST. I found some instruction here:
http://www.evanmiller.org/write-a-template-compiler-for-erlang.html

In README:
render(CompiledTemplate, Env)

In source code:
render(Template, Offset) ->
render(Template, [], Offset).