== Extending tcl to generate html ==

[CMcC] Following from [jenglish]'s comment: why learn to use a monster HTML-template library when you can, with a few lines of code, extend the base language so you can write things like [[<A> href "/home.html" { ! "Home" }]] ... I wrote the following to do just that using the techniques in [let unknown know].

 package require know
 know {[string match <*> [lindex $args 0]]} {
    set tag [string trim [lindex $args 0] "<>"]
    ::proc ::<$tag> {args} [string map [list @T $tag] {
	set result {}
	foreach {n v} [lrange $args 0 end-1] {
	    lappend result "$n='[armour $v]'"
	}
	return "<@T [join ${result}]>[lindex $args end]</@T>"
    }]
    return [eval $args]
 }

This will generate a proc for any command like [[<li>]] which will do pretty much what you'd expect it to.

----
== Armouring HTML ==

Prevent output from containing html-significant characters

 interp alias {} armour {} string map {& & < < > > \" " ' '} ... fairly clearly ''that'' needs some work :)

----
== Functional HTML generation ==

Often what you want isn't to iterate, but to convert a list into something else.  One generic technique I've found helpful is the use of [join], as follows:

  <ul><li>[[join $list </li></li>]</li></ul>

Which will convert a tcl list into an HTML unordered list.  Similar techniques are possible with <table>s

The technique can be readily made generic:

== Subst-if ==

Here's a variant of [if] which evaluates its conditional using [subst] and not [eval]

 proc If {args} {
    while {[llength $args] && ![uplevel expr [lindex $args 0]]} {
	set args [lrange $args 2 end]	;# lose the cond and positive-cond

	if {[lindex $args 0] eq "elseif"} {
	    set args [lrange $args 1 end]
	    continue	;# continue to evaluate conditionals
	} elseif {[lindex $args 0] eq "else"} {
	    break
	}
    }
    return [uplevel subst [list [lindex $args 1]]] ;# return with neg-consequence
 }

 set a 1; set b 2
 puts [If {$a} {a is true} else {a is false}]
 puts [If {$a == $b} {a == b} elseif {$b == 1} {b is 1} else {b is not 1 it is $b}]