Richard Suchenwirth 2002-12-16 - For people experienced in other languages, it may be interesting to compare code snippets between Tcl and other languages, to demonstrate similarities and differences. Please add more from your experience!
void countdown(int n) { | proc countdown {n} { int i; | for(i=n; i>0; i--) { | for {set i $n} {$i>0} {incr i -1} { printf("%d...\n", i); | puts $i... } | } } | }
C /* The above could be: */
void countdown(int n) { for (; n>0; n--) printf("%d...\n",n); }
AM The above proc could look like this in Fortran (90):
subroutine countdown( n ) integer :: n integer :: i do i = n,1,-1 write(*,*) i, '...' enddo endsubroutine
The main difference with either C or Tcl is that in Fortran the do-loop is very different kind of control construct: it is really an iteration over a predefined set of values, whereas in C and Tcl the three parts gouverning the iteration can be almost anything. (The Fortran control variable can be an integer only).
(define foo 42) | set foo 42 (define (square x) (* x x)) | proc square x {expr $x * $x} (define bar (square foo)) | set bar [square $foo] (define grill '(square foo)) | set grill {square $foo}
(define (abs x) | proc abs x { (cond ((> x 0) x) | expr { $x > 0? $x : ((= x 0) 0) | $x == 0? 0 : ((< x 0) (- x)))) | $x < 0? -$x} | } | or: proc abs x {expr abs($x)}
(define (abs x) | proc abs x { (if (< x 0) | if {$x < 0} { (- x) | expr -$x x)) | } else {return $x}
TV The C code from above:
int countdown(n) int n; { int i; for (i=n; i>0; i--) { printf("%d...\n", i); } }
in more traditional, non-cross source file argument checking, non-ansi notation, can also be represented in assembly code. For the above, using the gnu C compiler under cygwin, the following assembly can be generated, which looks obfuscated, because of the complex or hard to see through variable space and stack handling:
LC0: .ascii "%d...\12\0" .globl _countdown .def _countdown; .scl 2; .type 32; .endef _countdown: pushl %ebp movl %esp, %ebp subl $24, %esp movl 8(%ebp), %eax movl %eax, -4(%ebp) L10: cmpl $0, -4(%ebp) jg L13 jmp L11 L13: movl -4(%ebp), %eax movl %eax, 4(%esp) movl $LC0, (%esp) call _printf leal -4(%ebp), %eax decl (%eax) jmp L10 L11: leave ret
See also BOOK Programming Language Examples Alike Cookbook, http://www.merd.net/pixel/language-study/scripting-language/ and CL's ill-maintained personal notes on language comparison [L1 ].