Function: input
Section: programming/specific
C-Name: gp_input
Prototype:
Help: input(): read an expression from the input file or standard input.
Doc: reads a string, interpreted as a GP expression,
 from the input file, usually standard input (i.e.~the keyboard). If a
 sequence of expressions is given, the result is the result of the last
 expression of the sequence. When using this instruction, it is useful to
 prompt for the string by using the \kbd{print1} function. Note that in the
 present version 2.19 of \kbd{pari.el}, when using \kbd{gp} under GNU Emacs (see
 \secref{se:emacs}) one \emph{must} prompt for the string, with a string
 which ends with the same prompt as any of the previous ones (a \kbd{"? "}
 will do for instance).
