'''[http://www.schemers.org/%|%Scheme]''' is derivate of [Lisp].  A programming
language with even less syntax than Tcl itself. (but special forms and the
like...? [RS])

   ''Scheme is a lexically-scoped, block structured, dynamically typed, mostly functional language. It is a variant of Lisp. It has first-class procedures with  block structure and indefinite extent. Parameter passing is by value, but all  values are references. It has first-class continuations to allow the construction of new control abstractions. It has lexically-scoped ("hygienic") macros to allow definition of of new syntactic forms, or redefinition of old ones.'':   [ftp://ftp.cs.utexas.edu/pub/garbage/cs345/schintro-v14/schintro_toc.html%|%An Introduction to Scheme and its Implementation]



** See Also **

   [Biglook]:   

   [Muddy Scheme]:   a Scheme implementation in [Tcl]

   [Playing Scheme]:   
   
   [Tcl and LISP]:   
   
   [Playing LISP]:   
   
   [Serial summing]:   

   [Cameron Laird%|%Cameron Laird's] [http://phaseit.net/claird/comp.lang.scheme/scheme.html%|%personal notes on Scheme]:   

   [tcl-scheme] , by Ian Bicking :   a translation of Tcl into [Guile]/[Scheme]



** Reference **

   [BOOK Structure and Interpretation of Computer Programs%|%Structure and Interpretation of Computer programs] , by Harold Abelson , Gerald Jay Sussman , Julie Sussman:   

   [http://okmij.org/ftp/Scheme/monad-in-Scheme.html%|%Monadic Programming in Scheme]:   



** Tools **

   [PS/Tk]:   Portable Scheme interface to [Tk]

   [Chicken/Tk] , by [wdb%|%Wolf-Dieter Busch]:   An interface to Tk , based on [scheme_wish]

   [scheme_wish] , by Sven Hartrumpf:   a portable interface between Scheme and Tcl/Tk

   [Scheme Tk]:   a free R4RS Scheme interpreter that can access Tk. Concretely, it can be seen as the standard Tk package where Tcl has been replaced by a Scheme interpreter

   [Scheme Widget Library]:   a graphics package for [http://www.scheme.com/%|%Chez Scheme] , based on [Tk]




** Description **

[wdb]: I strongly disagree that Scheme has less syntax than Tcl! Reason: the symbols have a value ''per se''. Tcl has no symbols as $varname is just a shortcut for [[set varname]] where ''varname'' is just a constant, and the procedure addressed by ''set'' carries all the semantics. In Tcl, the command ''list unknown'' returns ''unknown'' because it is a constant. In Scheme, ''(list unknown)'' throws an error unless a symbol ''unknown'' is defined. If you want to list an unknown symbol, indeed, you need the special form ''(quote unknown)'' resp. its shortcut '' 'unknown''. 

   * In Lisp, the special form ''quote'' is essential. 
   * In Tcl, it is not necessary as it can be defined as a regular procedure as follows:

======
proc quote x {
    set x
}
======

(Thank you, [RS], for the hint with the combinator ''Identity''!)

----

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] $how
    }
}
======
======none
% define x 42
42
% define {+ x y} {expr {$x+$y}}
% + $x $x
84
======

This prevents us from having spaces in variable names (not a big problem), but presents the function name and arguments in one list, similar to how it will later be called - people sometimes wonder why we define `proc foo {x y} {..}` but call it `foo $x $y`...

<<categories>> Language | Functional Programming