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• criTiCaL - A TCL interpreter written in golang
• Building & Usage
• Examples
  • Available Commands
  • Features
  • Missing Features
• Testing
• See Also
• Bugs?

After re-readingTCL the Misunderstood, I decided to create a simple TCL evaluator of my own. This project is the result, and it has feature-parity with the two existing "small TCL" projects, written in C, which I examined:

• picol
  • By @antirez.
• partcl
  • By @zserge.

There is a simple introduction to this project, and TCL syntax, on my blog here:

• Writing a simple TCL interpreter in golang

The name of this project was generated by looking for words containing the letters "T", "C", and "L", in order. I almost chosearTiCLe,TreaCLe,myThiCaL, ormysTiCaL.Perhaps somebody else can write their own version of this project with one of those names!

This repository contains a TCL-like interpreter, along with a sample driver.

You can build both in the way you'd expect for golang applications:

$ go build.

Once built you can execute the application, supplying the path to a TCLscript which you wish to execute. For example:

    $ ./critical examples/prime.tcl    0    1    2 is prime    3 is prime    ..

The interpreter contains an embedded "standard-library", which you can view atstdlib/stdlib.tcl, which is loaded along with any file that you specify.

To disable the use of the standard library run:

   $ ./critical -no-stdlib path/to/file.tcl

Generally the point of a scripting language is you can embed it insidea (host) application of your own - exporting project-specific variablesand functions.

You'll find an example of doing that beneath theembedded/ directory:

• Embedding the criTiCaL interpreter

The following is a simple example program which shows what the code here looks like:

//// Fibonacci sequence, written in the naive/recursive fashion.//procfib {x} {if { <=$x 1 } {return 1    }else {return [expr [fib [expr$x - 1]] + [fib [expr$x - 2]]]    }}//// Lets run this in a loop//set i 0set max 20while {<=$i$max } {puts"Fib$i is[fib$i]"incr i}

Another example is the test-code which @antirez posted with hispicol writeup which looks like this:

procsquare {x} {    *$x$x}set a 1while {<=$a 10} {if {==$a 5} {puts {Missing five!}set a [+$a 1]continue    }puts"I can compute that$a*$a =[square$a]"set a [+$a 1]}

This example is contained within this repository aspicol.tcl, so you can run it directly:

     $ ./critical ./picol.tcl     I can compute that 1*1 = 1     I can compute that 2*2 = 4     ..

Additional TCL-code can be found beneathexamples/.

The following commands are available, and work as you'd expect:

• append,break,continue,decr,env,eval,exit,expr,for,if,incr,proc,puts,regexp,return,set,while.

The complete list of standardTCL commands will almost certainly never be implemented, but pull-request to add omissions you need will be applied with thanks.

Read the fileinput.tcl to get a feel for the language, but in-brief you've got the following facilities available:

• Floating-point mathematical operations forexpr
  • +-/*%.
• Comparison operations forexpr
  • <><=>=,==,!=,eq,ne
• Output to STDOUT viaputs.
• Inline command expansion, for exampleputs [* 3 4]
• Inline variable expansion, for exampleputs "$$name is $name".
• The ability to define procedures, viaproc.
  • See the later examples, or examine code such asexamples/prime.tcl.

The biggest missing feature is the complete absence of support for lists of any kind. This is common in the more minimal-TCL interpreters I examined.

The other obvious missing feature is support for theupvalue command, which means we're always a little at risk of scope-related issues.

Addingupvalue would be possible, but adding list-processing would be more work than I'd prefer to carry out at this time - see #19 for details of what would be required to implement this support.

Our code has 100% test-coverage, which you can exercise via the standard golang facilities:

$ gotest ./...

There are also fuzz-based testers supplied for thelexer andparser packages, to run these run one of the following two sets of commands:

cd parsergotest -fuzztime=300s -parallel=1 -fuzz=FuzzParser -v

cd lexergotest -fuzztime=300s -parallel=1 -fuzz=FuzzLexer -v

This repository was put together afterexperimenting with a scripting language, anevaluation engine, putting together aFORTH-like scripting language, writing aBASIC interpreter and creatingyet another lisp..

I've also played around with a couple of compilers which might be interesting to refer to:

• Brainfuck compiler:
  • https://github.com/skx/bfcc/
• A math-compiler:
  • https://github.com/skx/math-compiler

Please feel free to open a new issuewith your example included so I can see how to fix it.

Steve