Re: [dev] nscript - a little stack-based scripting language interpretter I wrote

On Wed, 25 Aug 2010, yy wrote:

> It is difficult to form an opinion about a language if there is no
> documentation or any examples, and it is difficult to form an opinion
> about the implementation without understanding the language.
>
> What features does it have? How does it look like? How does it compare
> to other stack-based languages like toka or raven?

It's not really very big actually. I don't think anyone could (or would
want to) actually /use/ it, so I didn't include much documentation.

But it looks like this -

Comments start with '#' and continue till the end of the line. For now
there are just 5 types - 'boolean', 'integer', 'string', 'function' and
'block'. Strings are delimited by single quotes.

To push the integer 2 onto the stack:-

      2

'print' will pop and print the last object on the stack

      2 print # prints '2'

'+' pops the last two integers on the stack, and pushes their sum
(implementation-wise it just pops and adds the last integer into the
second-last)

      2 3 + print # prints '5'

Preceding a name with '$' will create a variable with that name and pop
and assign the last thing on the stack to it. Simply a name will push
the value of the variable with that name onto the stack (if it's not
executable, we're getting to executables soon).

      3 $var 2 5 var + print # prints '8', 2 is left on stack

Putting code between '{' and '}' will push a block onto the stack, with
that code in it. This can be used with, for example, the 'repeat'
function, like this

      { 'hi' print } 3 repeat # prints 'hihihi'

You can make your own functions by assigning blocks to variables. When
you write a name, and it refers to a variable that's executable (a
block) then it gets executed.

      { 3 + print } $print3greater

      5 print3greater # prints '8'

You can push a block-variable onto the stack without executing it by
prefixing it with an '&'. This can be done for built-in functions too.

      1 2 3 4 &add 3 repeat print # prints '10'

Here's some example factorial code:-

     { dup 0 == { 1 + } { 1 rot { dup 1 + } rot 1 - dup $oneless repeat &* oneless repeat } ifelse } $fact

     10 fact print # prints 10 factorial, that is '3628800'

'==' pops two objects, and pushes back 'true' if they are equal, else
'false'

'dup' duplicates the last object on the stack

'ifelse' executes the block at 1 on the stack if boolean at 2 is true,
else executes the block at 0 (the last object on stack is at 0, the
second last at 1, and so on).

'rot' swaps the last two objects on the stack

'fact' works by pushing 1 to n onto the stack first and then multiplying them
together at the end. For 0 it just gives 1.

There's a clearer version of 'fact' with comments in nstest.c. (it
doesn't work for '0' input though - I will update the code).
Received on Wed Aug 25 2010 - 02:24:03 CEST