:begin
>.v_exist[a#] .then[intro]
>.define[a#] .define[b#] .define[c#]
>.define[a]
>.window[]
>intro

:Intro
 Iris uses two types of variables: text and numeric.

 Iris also supports a number of arithmetic and logical
 operators.

 When numeric variables are being used, the operators use
 their conventional meaning.  However, when text variables
 are being used the meaning of the operators is slightly
 different.

 You can mix numeric and text variables in a calculation or
 comparison whenever you want.  Which "type" of operation
 takes place -- text or numeric -- depends on the variable
 first mentioned.  Variables of another type are converted
 to the "base" type.

 If a text variable needs to be converted to a numeric
 variable, but contains no numerals, zero is used.

 Here are some sample calculations.

:calcs
>a#=10 b#=20 c#=30 a=10
 numeric                   text
 -------                   ----
 a# = ^a#                 | a = ^a

>a#+1 a+1
 add:      a# + 1 = ^a#   | append:   a + 1 = ^a

>a#-1 a-1
 subtract: a# - 1 = ^a#   | delete:   a - 1 = ^a

>a#*2 a*2
 multiply: a# * 2 = ^a#   | fill:     a * 2 = ^a

>a#/2 a/2
 divide:   a# / 2 = ^a#   | withdraw: a / 2 = ^a

>.pause
>a#=^b#+^c# a=^b#+^c#
 numeric                           text
 -------                           ----
 a# = b# + c# .. ^a# = ^b# + ^c#    | a = b# + c# .. ^a = ^b# + ^c#

>a#=^b#-^c# a=^b#-^c#
 a# = b# - c# .. ^a# = ^b# - ^c#   | a = b# - c# .. ^a = ^b# - ^c#

>a#=^b#*^c# a=^b#*^c#
 a# = b# * c# .. ^a# = ^b# * ^c#   | a = b# * c# .. ^a = ^b# * ^c#

>a#=^b#/^c# a=^b#/^c#
 a# = b# / c# .. ^a# = ^b# / ^c#     | a = b# / c# .. ^a = ^b# / ^c#
*