HELP DECIMALS            Mark Rubinstein, December 1984, A.S. Oct 1986

For a tutorial introduction to the different kinds of numbers that
POPLOG recognises and uses see TEACH DECIMALS.

POPLOG has several kinds of numbers -
    integers,
    bigintegers,
    decimals ("reals")
    double decimals (called "ddecimals" in POPLOG)
    complex numbers
    ratios

*DDECIMAL numbers are more accurate (contain more significant digits)
than DECIMAL numbers. The other side of the coin is that POPLOG has to
use more memory to store them, and their use can cause additional
"garbage collections".

When a number is read (from a file or from the terminal) without a
decimal point, an INTEGER is created.  If a decimal point is read then a
DDECIMAL is created. However if the result of a computation is a real
number then POPLOG returns a DECIMAL number,  e.g.

    dataword(1) =>
    ** integer

    dataword(4.5) =>
    ** ddecimal

    dataword(9/2) =>
    ** decimal

(See HELP *DATAWORD).

POPLOG can be made to return DDECIMAL numbers by assigning TRUE to
POPDPRECISION (see REF *POPDPRECISION).

It is also possible to ensure that a number read in is either a single
or double precision number, by using "s0" or "d0" at the end, e.g.

    dataword(1.0s0) =>
    ** decimal

    dataword(1.0d0) =>
    ** ddecimal

An "exponent" notation is available for decimals using "e" followed by
the power of 10 to be used:
    3.123e3 =>
    ** 3123.0

    3.123e-3 =>
    ** 0.003123


If, instead of "e" "s" is used, the number will be read as a SINGLE
decimal number,e.g.

    3.123s-3=>
    ** 0.003123

-- See also ------------------------------------------------------------

    HELP    *NUMBERS      - on number datatypes in POP-11, and
                            procedures which operate on them.
    REF     *ITEMISE      - on the workings of the itemiser, and textual
                            representations of all POP-11 datatypes.
    HELP    *PRINT        - on the POP-11 printing mechanism.
    HELP    *BIGINTEGERS  - on bigintegers.
    REF     *NUMBERS      - technical overview of numbers and associated
                            procedures.

--- C.all/help/decimals ------------------------------------------------
--- Copyright University of Sussex 1987. All rights reserved. ----------