bradfordvt / pypicotcl

Small Tool Command Language (Tcl) Interpreter written in Python

pypicotcl

Small Tool Command Language (Tcl) Interpreter written in Python

Tool Command Language (Tcl) interpreter written in Python. The interpreter is just a core interpreter and not a comprehensive implementation of the complete command language. This was written to be able to extend to create an interpreter for IEEE Std 1687 Procedural Description Language (PDL) for EDA tools.

The inspiration for this code is based on the C code located at: http://oldblog.antirez.com/post/picol.html. Major changes different from this code include making the parser and interpreter class based. Enhancements to the Tcl commands like puts and if are also to be included to make them more compliant to Tcl.

pypicotcl package

The pypicotcl package contains the pypicotcl.py module which contains all the core classes and code for the interpreter. Specialized classes can be created to inherit the core interpreter and add additional commands to the interpreter. To add additional commands, the derived class would call the register_command() method of the core interpreter similar to how the register_core_commands() works. The derived class must also call the register_core_commands() of the core interpreter to get the core commands installed. A sample of the kind of Tcl code supported is shown below:

if [+ 1 2] {
   puts "+ 1 2 is true"
}
if [+ 7 -7] {
   puts "+ 7 -7 is true"
} else {
   puts "+ 7 -7 is false"
}
puts "Hello World!"
set v "foobar"
puts "v is $v"

puts -nonewline "First message..."
puts "ok"

puts stderr "This sent to stderr"

set b "stderr"
puts $b "b sent to stderr"

The parser is very similar to the Tcl one, pypicotcl supports interpolation as well, for example you can write:

set a "pu"
set b {ts}
$a$b "Hello World!"

Note that pypicotcl has an interactive shell! so just launch it without arguments to start to play (to run just write python pypicotcl.py).

To run a program stored in a file instead use python pypicotcl.py filename.tcl.

A Raw list of the supported features:

• Interpolation, as seen above. You can also write "2+2 = [+ 2 2]" or "My name is: $foobar".
• Procedures, with return. Like Tcl if return is missing the result of the last command executed is returned.
• If, if .. else .., while with break and continue
• Recursion
• Variables inside procedures are limited in scope like Tcl, i.e. there are real call frames in Picol.
• The following other commands: set + - * / == != > < >= <= puts

This is an example of programs pypicotcl can run:

proc fib {x} {
    if {<= $x 1} {
        return 1
    } else {
        + [fib [- $x 1]] [fib [- $x 2]]
    }
}

puts [fib 20]

Another example:

proc square {x} {
    * $x $x
}

set a 1
while {<= $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]
}