Stack traces: Difference between revisions

=={{header|Quackery}}==

Quackery has two system stacks, the call or return stack and a data stack. The words <code>echoreturn</code> and <code>echostack</code> display the current state of them. Each call to a word or nest places two entries on the return stack, a pointer to the word or nest, and an index into that word or nest. These are displayed as the name of the word, or <code>[...]</code> for an unnamed nest, and the index into the word or nest as an integer. Pairs of entries are displayed wrapped in braces, e.g. <code>{shell 5}</code>.

This is illustrated with a Quackery shell dialogue. The Quackery shell is written in Quackery, and as can be seen, occupies five pairs of entries on the return stack. After each interaction with the user the data stack is automatically displayed. Here the user opens the Quackery shell, displays the return stack, defines a naive recursive Fibonacci word that displays the return and data stack at the start of each call, and uses it to compute and display the fifth Fibonacci number (5).

<pre> > quackery

Welcome to Quackery.

Enter "leave" to leave the shell.

Building extensions.

/O> echoreturn

...

{[...] 0} {quackery 1} {[...] 11} {shell 5} {quackery 1} {[...] 0}

Stack empty.

/O> [ cr echoreturn

... cr echostack

... dup 2 < if done

... dup 1 - swap 2 -

... recurse swap recurse + ] is fib

...

Stack empty.

/O> 5 fib echo

...

{[...] 0} {quackery 1} {[...] 11} {shell 5} {quackery 1} {[...] 1} {fib 1}

Stack: 5

{[...] 0} {quackery 1} {[...] 11} {shell 5} {quackery 1} {[...] 1} {fib 15} {recurse 1} {fib 1}

Stack: 4 3

{[...] 0} {quackery 1} {[...] 11} {shell 5} {quackery 1} {[...] 1} {fib 15} {recurse 1} {fib 15} {recurse 1} {fib 1}

Stack: 4 2 1

{[...] 0} {quackery 1} {[...] 11} {shell 5} {quackery 1} {[...] 1} {fib 15} {recurse 1} {fib 17} {recurse 1} {fib 1}

Stack: 4 1 2

{[...] 0} {quackery 1} {[...] 11} {shell 5} {quackery 1} {[...] 1} {fib 15} {recurse 1} {fib 17} {recurse 1} {fib 15} {recurse 1} {fib 1}

Stack: 4 1 1 0

{[...] 0} {quackery 1} {[...] 11} {shell 5} {quackery 1} {[...] 1} {fib 15} {recurse 1} {fib 17} {recurse 1} {fib 17} {recurse 1} {fib 1}

Stack: 4 1 0 1

{[...] 0} {quackery 1} {[...] 11} {shell 5} {quackery 1} {[...] 1} {fib 17} {recurse 1} {fib 1}

Stack: 2 4

{[...] 0} {quackery 1} {[...] 11} {shell 5} {quackery 1} {[...] 1} {fib 17} {recurse 1} {fib 15} {recurse 1} {fib 1}

Stack: 2 3 2

{[...] 0} {quackery 1} {[...] 11} {shell 5} {quackery 1} {[...] 1} {fib 17} {recurse 1} {fib 15} {recurse 1} {fib 15} {recurse 1} {fib 1}

Stack: 2 3 1 0

{[...] 0} {quackery 1} {[...] 11} {shell 5} {quackery 1} {[...] 1} {fib 17} {recurse 1} {fib 15} {recurse 1} {fib 17} {recurse 1} {fib 1}

Stack: 2 3 0 1

{[...] 0} {quackery 1} {[...] 11} {shell 5} {quackery 1} {[...] 1} {fib 17} {recurse 1} {fib 17} {recurse 1} {fib 1}

Stack: 2 1 3

{[...] 0} {quackery 1} {[...] 11} {shell 5} {quackery 1} {[...] 1} {fib 17} {recurse 1} {fib 17} {recurse 1} {fib 15} {recurse 1} {fib 1}

Stack: 2 1 2 1

{[...] 0} {quackery 1} {[...] 11} {shell 5} {quackery 1} {[...] 1} {fib 17} {recurse 1} {fib 17} {recurse 1} {fib 17} {recurse 1} {fib 1}

Stack: 2 1 1 2

{[...] 0} {quackery 1} {[...] 11} {shell 5} {quackery 1} {[...] 1} {fib 17} {recurse 1} {fib 17} {recurse 1} {fib 17} {recurse 1} {fib 15} {recurse 1} {fib 1}

Stack: 2 1 1 1 0

{[...] 0} {quackery 1} {[...] 11} {shell 5} {quackery 1} {[...] 1} {fib 17} {recurse 1} {fib 17} {recurse 1} {fib 17} {recurse 1} {fib 17} {recurse 1} {fib 1}

Stack: 2 1 1 0 1

5

Stack empty.

/O></pre>