SNOBOL, or StriNg Oriented and symBOlic Language, is a programming language emphasizing text processing and pattern matching.

See Also  edit

TkS*LIDE

an IDE for SNOBOL4 writtin in Tk

Documentation  edit

SNOBOL4TCL

Tcl/Tk interface of CSNOBALL4

Ralph Griswold

created both SNOBOL and Icon

Description  edit

Having actually tried to learn this language, I'm astounded by its pattern matching facilities. Makes grep look primitive.

COMIT was a predecessor of SNOBOL.

Discussion  edit

BMA: Being a slow starter with Tcl, where would I start trying to

1. write a snobol interpreter in Tcl, or
2. write snobol pattern matching tools in Tcl?

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LV: Well, the quick approach would be to scavenge one of the free snobol interpreter source trees for their code, write or wrap the code with Tcl binding, and invoke it directly.

The tougher approach would be to study the language, determine what features from the language you want, decide upon the Tcl API you want to use to achieve similar functionality, then write that functionality, write a test suite, and get it all running.

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escargo 2003-12-30: I will just note that the successor to Snobol, Icon, also has a page on this wiki. Its pattern matching is different than Snobol's, but also very powerful. It is not based on regular expressions, but does pattern matching with other facilities.

LES: If it ain't regular expressions, it ain't no good.

Larry: Les's ideas are no better than his grammar. The only advantage of regular expressions over Snobol pattern matching and Icon string scanning is that regular expressions are very terse. Perhaps because of their terseness, they quickly become unreadable as they become more complex. Pattern matching and string scanning are far more powerful, are quicker to write, and are far easier to debug. One writer said that if you have a problem and you solve it with a regular expression, you end up with two problems. If you need to do anything complex with strings, your best bet is Icon string scanning.

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Perhaps someone could put up some examples of the power of snobol, demonstrating the power being described specifically. Then if someone wants to wander by and contribute regular expression equivalents, the reader will more easily be able to take sides in the debate.

Tcl/Tk Interface  edit

-INCLUDE 'stcl.sno'
      INTERP = STCL_CREATEINTERP()
      TCL_VERSION = STCL_GETVAR(INTERP, "tcl_version")
      OUTPUT = IDENT(TCL_VERSION) "Could not get tcl_version" :S(END)
      OUTPUT = "Tcl Version: " TCL_VERSION

* check Tcl version
      NUM = SPAN('0123456789')
      VPAT = NUM '.' NUM
      TCL_VERSION VPAT . VER                          :S(CHECKV)
      OUTPUT = "could not parse tcl_version"          :(END)

CHECKV  LT(VER, 8.4)                                    :S(CHECKTK)

* Tcl 8.4 and later can dynamicly load Tk!
      STCL_EVAL(INTERP, "package require Tk")         :F(END)

* Check for Tk

CHECKTK TK_VERSION = STCL_GETVAR(INTERP, "tk_version")  :F(NOTK)
      DIFFER(TK_VERSION)                              :S(HAVETK)

NOTK    OUTPUT = "Could not find tk_version"            :(END)

HAVETK  OUTPUT = "Tk version: " TK_VERSION
      SEP = ';'

      STCL_EVAL(INTERP,
+               'button .hello -text "Hello, world" -command {set foo 1}' SEP
+               "pack .hello" SEP
+               'button .other -text "Other Choice" -command {set foo 2}' SEP
+               "pack .other" SEP
+               "global foo" SEP
+               "vwait foo")

      OUTPUT = STCL_GETVAR(INTERP, "foo")
END

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