"It might be possible to embed a C compiler into a PDF by compiling it to JS with Emscripten, for example, but then your C compiler has to take input through a plain-text form field and spit its output back through a form field."
• Just showing the user text? Compiles to plaintext.
• Get the user to give some input? Compiles to a styled form, as PostScript.
• Add radio buttons? Compiles to a physical form but with a 3D-printed notched slider glued to it.
• Require validation for freeform-text form fields? Compiles to a 3D-print + VLSI + pick-and-place specification for a tablet embedded-device that displays the form and does the validation.
Now imagine a "printer" that takes such abstract documents as input, and can print any of these... :)
it doesn't actually execute code, right? Then what's the power of having a compiler in a PDF? you can output the executable, but can you run it?
also, is the "input" and "output" of this compiler just code and executables?
> also, is the "input" and "output" of this compiler just code and executables?
Mostly yes. I'm not sure how much of a typical build chain he was trying to convert to JS here, but the compiler itself typically takes a bunch of files with C code and outputs a number of "object files", which are really chunks of machine code. In an actual build process, you'd then use a linker to glue those object files together in the right way and make an executable.
I guess, what you could do if you wanted was to include the whole build chain (including linker) into the PDF, encode the executable as Base64 and fill some form field of the PDF with it. Then your workflow would be as follows:
1) Write some C code
2) Copy the C code into form field #1 if the PDF.
3) Hit a "compile" button or something. Form field #2 fills with what looks like an enormous amount of random gibberish (really the Base64-encoded binary)
5) Copy all the text from form field #2, use a program of your choice to decode the Base64 and save the decoded binary on your hard drive.
6) Run the binary on your hard drive and watch your C code execute. Hooray!
Depends what you mean by "run", really. You can write a full-on X86 emulator, and execute a compiled binary there. But given that it's an emulator running in a nested series of sandboxes, it won't be terribly useful -- for example, it still won't have I/O capabilities.