FF 2007-30-05 - The discussion evolved in ToW Tcl on WebFreeWay has generate some interest, and here is an effort for making a minimal template engine. I would like to use this page for collecting ideas from people. Fell free to change everything, fix bugs and revolutionize the concept - it is the purpose of the page.
Here's how it is (initially) supposed to work:
first, let's create a template file (templtest.tmpl):
<table><%
for {set i 0} {$i < 4} {incr i} { %>
<tr>
<td><%= $i %></td>
</tr><%
} %>
</table>now run it:
source TemplaTcl TemplaTcl::parseFile templtest.tmpl TemplaTcl::dump
and here's the output that gets produced:
<table>
<tr>
<td>0</td>
</tr>
<tr>
<td>1</td>
</tr>
<tr>
<td>2</td>
</tr>
<tr>
<td>3</td>
</tr>
</table>Description: really, this engine it works by converting the whole template into a Tcl script, and then running it. This approach maybe it has pro and cons. I see the only pro that is very flexible and it leaves you maximum freedom of doing what you want, dealing with any data and putting how much code you want in the template (although the template should possibly hold minimum code - according to MVC, just the presentation logic, no code related to controller logic, state persistance, or data-retrieval logic).
The above example generates this "middle" code:
puts -nonewline <table>
for {set i 0} {$i < 4} {incr i} {
puts -nonewline {
<tr>
<td>}
puts -nonewline $i
puts -nonewline {</td>
</tr>}
}
puts -nonewline {
</table>
}(you can see that by replacing eval with puts)
#!/usr/bin/env tclsh
# tcllib required
package require Tcl 8.2
package require struct
namespace eval TemplaTcl {
variable data
variable mode
variable modeprev
proc parseFile {file} {
set fh [open $file r]
set raw [read $fh]
close $fh
return [parse $raw]
}
proc parse {template} {
variable data
variable mode
variable modeprev
set mode raw
mode raw
::struct::queue cc
set rawl [split $template {}]
foreach ch $rawl {
# we work char-by-char :|
cc put $ch
# max block to compare (<%=) is 3 chars long:
if {[cc size] >= 3} {
set s3 [join [cc peek 3] {}]
set s2 [join [cc peek 2] {}]
if {$mode == "raw"} {
if {$s3 == "<%="} {
# <%= is a shorthand for puts ...
cc get 3
mode code
buf "puts -nonewline "
continue
} elseif {$s2 == "<%"} {
# <% indicates begin of a code block
cc get 2
mode code
continue
}
} elseif {$mode == "code"} {
if {$s2 == "%>"} {
# and %> is the end of code block
cc get 2
mode raw
continue
}
}
buf [cc get]
}
}
# finish working on the queue:
while {[cc size] > 0} {
buf [cc get]
}
mode flush
}
proc mode {m} {
# used internally by parse - switches mode and stuff...
variable data
variable mode
variable modeprev
set newm {}
switch $m {code - raw {set newm $m}}
if {$newm != {}} {
set modeprev $mode
set mode $newm
set data(buf:$mode) {}
}
if {$m == "flush"} {set modeprev $mode ; set mode _}
if {$mode != $modeprev} {
lappend data(out) [list $modeprev $data(buf:$modeprev)]
set data(buf:$modeprev) {}
}
}
proc buf {ch} {
# used internally by parse - put $ch in the right buffer
variable data
variable mode
append data(buf:$mode) $ch
}
proc dump {} {
# run the template script
variable data
set tclBuf ""
foreach l $data(out) {
set t [lindex $l 0]
set d [lindex $l 1]
switch $t {
raw {append tclBuf [list puts -nonewline $d]\n}
code {append tclBuf $d\n}
}
}
eval $tclBuf
}
}escargo - I think it's a mistake to have parse read a file; it would be potentially more flexible to use if it just took a string to process as input, and let the caller determine where the string comes from. FF - good point! (changed)
APW Just found textutil::expander[L1 ] package in tcllib, which is included in ActiveTcl 8.4.14.0. Have the feeling it does something similar, maybe it's worth looking at it.