diff options
Diffstat (limited to 'tcl.html.markdown')
| -rw-r--r--[-rwxr-xr-x] | tcl.html.markdown | 61 |
1 files changed, 34 insertions, 27 deletions
diff --git a/tcl.html.markdown b/tcl.html.markdown index 198f675e..b90bd690 100755..100644 --- a/tcl.html.markdown +++ b/tcl.html.markdown @@ -14,7 +14,7 @@ programming language. It can also be used as a portable C library, even in cases where no scripting capability is needed, as it provides data structures such as dynamic strings, lists, and hash tables. The C library also provides portable functionality for loading dynamic libraries, string formatting and -code conversion, filesystem operations, network operations, and more. +code conversion, filesystem operations, network operations, and more. Various features of Tcl stand out: * Convenient cross-platform networking API @@ -58,14 +58,14 @@ lighter that that of Lisp, just gets out of the way. #! /bin/env tclsh ################################################################################ -## 1. Guidelines +## 1. Guidelines ################################################################################ # Tcl is not Bash or C! This needs to be said because standard shell quoting # habits almost work in Tcl and it is common for people to pick up Tcl and try # to get by with syntax they know from another language. It works at first, # but soon leads to frustration with more complex scripts. - + # Braces are just a quoting mechanism, not a code block constructor or a list # constructor. Tcl doesn't have either of those things. Braces are used, # though, to escape special characters in procedure bodies and in strings that @@ -73,7 +73,7 @@ lighter that that of Lisp, just gets out of the way. ################################################################################ -## 2. Syntax +## 2. Syntax ################################################################################ # Every line is a command. The first word is the name of the command, and @@ -83,13 +83,13 @@ lighter that that of Lisp, just gets out of the way. # are used, they are not a string constructor, but just another escaping # character. -set greeting1 Sal +set greeting1 Sal set greeting2 ut set greeting3 ations #semicolon also delimits commands -set greeting1 Sal; set greeting2 ut; set greeting3 ations +set greeting1 Sal; set greeting2 ut; set greeting3 ations # Dollar sign introduces variable substitution @@ -121,15 +121,16 @@ puts lots\nof\n\n\n\n\n\nnewlines # A word enclosed in braces is not subject to any special interpretation or -# substitutions, except that a backslash before a brace is not counted when look#ing for the closing brace +# substitutions, except that a backslash before a brace is not counted when +# looking for the closing brace set somevar { This is a literal $ sign, and this \} escaped brace remains uninterpreted -} +} # In a word enclosed in double quotes, whitespace characters lose their special -# meaning +# meaning set name Neo set greeting "Hello, $name" @@ -148,6 +149,9 @@ set greeting "Hello, [set {first name}]" # To promote the words within a word to individual words of the current # command, use the expansion operator, "{*}". +``` + +```tcl set {*}{name Neo} # is equivalent to @@ -163,7 +167,7 @@ set greeting "Hello, $person(name)" # A namespace holds commands and variables namespace eval people { namespace eval person1 { - set name Neo + variable name Neo } } @@ -174,7 +178,7 @@ set greeting "Hello $people::person1::name" ################################################################################ -## 3. A Few Notes +## 3. A Few Notes ################################################################################ # All other functionality is implemented via commands. From this point on, @@ -189,7 +193,10 @@ set greeting "Hello $people::person1::name" namespace delete :: -# Because of name resolution behaviour, it's safer to use the "variable" command to declare or to assign a value to a namespace. +# Because of name resolution behaviour, it's safer to use the "variable" command to +# declare or to assign a value to a namespace. If a variable called "name" already +# exists in the global namespace, using "set" here will assign a value to the global variable +# instead of creating a new variable in the local namespace. namespace eval people { namespace eval person1 { variable name Neo @@ -203,7 +210,7 @@ set people::person1::name Neo ################################################################################ -## 4. Commands +## 4. Commands ################################################################################ # Math can be done with the "expr" command. @@ -256,7 +263,7 @@ proc greet greeting\ name return\ \"Hello,\ \$name! proc fold {cmd args} { set res 0 foreach arg $args { - set res [cmd $res $arg] + set res [$cmd $res $arg] } } fold ::tcl::mathop::* 5 3 3 ;# -> 45 @@ -288,7 +295,7 @@ while {$i < 10} { # A list is a specially-formatted string. In the simple case, whitespace is sufficient to delimit values -set amounts 10\ 33\ 18 +set amounts 10\ 33\ 18 set amount [lindex $amounts 1] @@ -332,7 +339,7 @@ eval {set name Neo} eval [list set greeting "Hello, $name"] -# Therefore, when using "eval", use [list] to build up a desired command +# Therefore, when using "eval", use [list] to build up a desired command set command {set name} lappend command {Archibald Sorbisol} eval $command @@ -348,8 +355,8 @@ eval $command ;# There is an error here, because there are too many arguments \ # This mistake can easily occur with the "subst" command. set replacement {Archibald Sorbisol} set command {set name $replacement} -set command [subst $command] -eval $command ;# The same error as before: to many arguments to "set" in \ +set command [subst $command] +eval $command ;# The same error as before: too many arguments to "set" in \ {set name Archibald Sorbisol} @@ -357,12 +364,12 @@ eval $command ;# The same error as before: to many arguments to "set" in \ # command. set replacement [list {Archibald Sorbisol}] set command {set name $replacement} -set command [subst $command] +set command [subst $command] eval $command # It is extremely common to see the "list" command being used to properly -# format values that are substituted into Tcl script templates. There are +# format values that are substituted into Tcl script templates. There are # several examples of this, below. @@ -415,12 +422,12 @@ proc while {condition script} { # The "coroutine" command creates a separate call stack, along with a command # to enter that call stack. The "yield" command suspends execution in that -# stack. +# stack. proc countdown {} { #send something back to the initial "coroutine" command yield - set count 3 + set count 3 while {$count > 1} { yield [incr count -1] } @@ -428,12 +435,12 @@ proc countdown {} { } coroutine countdown1 countdown coroutine countdown2 countdown -puts [countdown 1] ;# -> 2 -puts [countdown 2] ;# -> 2 -puts [countdown 1] ;# -> 1 -puts [countdown 1] ;# -> 0 +puts [countdown 1] ;# -> 2 +puts [countdown 2] ;# -> 2 +puts [countdown 1] ;# -> 1 +puts [countdown 1] ;# -> 0 puts [coundown 1] ;# -> invalid command name "countdown1" -puts [countdown 2] ;# -> 1 +puts [countdown 2] ;# -> 1 ``` |