How do you use #call directive for Red function with string datatypes as parameters?

Question

Given a script, such as below, which does not compile yet, how can I use #call to use my Red function from within Red/System?

Red []

pff: function [a [string!] ][print a]  

#system [
    #call [pff "hello"]    
]

There is a type mismatch. What do you need to do to convert the string to the proper Red/System datatype?

Answer 1

To expand on Peter's correct answer, in this particular case, you need to internalize the c-string as a red-string!, using string/load, like this:

Red []

pff: function [a [string!] ][print a]  

#system [
    s: "hello"
    hello: string/load s 1 + length? s UTF-8
    #call [pff hello]
]

Notes:

• Red/System's strings are ASCII only for now, so you need to specify UTF-8 as the source encoding format.

• You need to pass the size of the c-string accounting for the terminal NUL (hence the + 1).

The internal API is not documented as it is not finalized. Feel free to ask here or on our other communication channels if you need any info about it.

Answer 2

You need to make calls to the Red runtime API to perform the transformation. The Red runtime API isn't documented yet so you either have to read the code or ask one of the few people who are familiar with it. (I did a little of both).

I wrote a function to convert a Red string! to a UTF-8 encoded Red/System c-string!, it's on github.