A derivate of [Lisp]. A programming language with even less syntax than Tcl itself. (but special forms and the like...? [RS])

See [Tcl and LISP] | [Playing LISP] | [Serial summing].

There's a [Tk]Scheme.  [[maybe more than one?]]

The classic Scheme book is [SICP].













http://phaseit.net/claird/comp.lang.scheme/scheme.html
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One interesting difference is that setting of (only global?) variables and function definition both are done with ''define'', which creates a lambda if its first element is a list. Just for experimenting, here's how to have that in Tcl:
 proc define {what how} {
     if {[llength $what]==1} {
          uplevel 1 set $what [list $how]
     } else {
          proc [lindex $what 0] [lrange $what 1 end] $how
     }
 }
 % define x 42
 42
 % define {+ x y} {expr {$x+$y}}
 % + $x $x
 84

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[Category Language]