By default, the text interpreter processes input from the user input device (the keyboard) when Forth starts up. The text interpreter can process input from any of these sources:
A program can identify the current input device from the values of
source-id– 0 | -1 | fileid core-ext,file “source-i-d”
Return 0 (the input source is the user input device), -1 (the
input source is a string being processed by
a fileid (the input source is the file specified by
blk– addr block “b-l-k”
uvar variable – This cell contains the current
block number (or 0 if the current input source is not a block).
save-input– x1 .. xn n core-ext “save-input”
The n entries xn - x1 describe the current state of the
input source specification, in some platform-dependent way that can
be used by
restore-inputx1 .. xn n – flag core-ext “restore-input”
Attempt to restore the input source specification to the state described by the n entries xn - x1. flag is true if the restore fails. In Gforth with the new input code, it fails only with a flag that can be used to throw again; it is also possible to save and restore between different active input streams. Note that closing the input streams must happen in the reverse order as they have been opened, but in between everything is allowed.
evaluate... addr u – ... core,block “evaluate”
Save the current input source specification. Store
0 and make the string c-addr u the input source and
input buffer. Interpret. When the parse area is empty, restore the
input source specification.
query– core-ext-obsolescent “query”
Make the user input device the input source. Receive input into
the Terminal Input Buffer. Set
>IN to zero. OBSOLESCENT: