The fry vocabulary implements fried quotation. Conceptually, fried quotations are quotations with “holes” (more formally, fry specifiers ), and the holes are filled in when the fried quotation is pushed on the stack.
Fried quotations are started by a special parsing word:
Fry is implemented as a parsing word which reads a quotation and scans for occurrences of _ and @; these words are not actually executed, and doing so raises an error (this can happen if they're accidentally used outside of a fry).
Fried quotations can also be constructed without using a parsing word; this is useful when meta-programming: