# Calling Retro from C

The C implementation of Retro provides several functions for
interacting with code written in Retro.

## Dictionary

The dictionary is a linked list, with a pointer to the most
recent entry stored in address 2.

You can access the fields for each entry using:

    d_link
    d_xt
    d_class
    d_name

Each takes a dictionary header address (the "dictionary token")
and returns a pointer to the Retro address for the desired data.

To find a dictionary token, use `d_lookup`. This takes the address
of the dictionary to search (`memory[2]` in most cases) and the
name of the word to find.

There is also `d_xt_for()` which takes a name and a dictionary
pointer and returns the execution token for the specified word.

## Strings

Like C, Retro uses NUL terminated strings. But, since all
addressing is 32-bit (or 64-bit, depending on your configuration),
some conversion is needed.

To get a C version of a string, use `string_extract()`. This takes
a Retro address and returns a pointer to a C string.

Example:

    // Get the name of the most recently defined word
    string_extract(d_name(memory[2]));

To push a C string into Retro memory, use `string_inject()`. This
takes a C string and a Retro address.

    // Copy a string to the TIB buffer
    string_inject("hello", 1024);

## Stack

You can push values to the stack with `stack_push()` and pop them
off with `stack_pop()`.

## Interacting

If you have a word named `hello` that you wish to run:

    execute(d_xt_for("hello", memory[2]));

If you want to evaluate a token as if it was typed into a Retro
listener:

    string_inject("token", 1024);
    stack_push(1024);
    execute("interpret", memory[2]);

The `interpret` word handles things like prefixes, so this is
needed if you want to run something that needs those.