Re: LIterate programming with calc (help)

[Christian Moe <mail@christianmoe.com>]

Fraga, Eric writes:

> On Monday, 24 Oct 2022 at 09:20, Ihor Radchenko wrote:
>> I vaguely recall that storing variables in calc is something like
>> variable := assignment (which is actually rewrite rule, but that's how
>> 13.1 Storing Variables section of the calc manual explains variable
>> assignments).
>
> That is true for embedded calc (which I use all the time) but I cannot
> seem to get this to work for src blocks:


Same: it requires using the `s s' (calc-store) command, though (which
can also be done without the := assignment operator), and I've searched
the manual without spotting a way to do that with algebraic entry and
hence in a src block, as there doesn't seem to be any corresponding
command. I hope there is a way, though!

As an unsatisfying workaround, one could use :var header arguments; they
work up to a point, but not with units, as Ypo wants to use (and which
are are a really cool thing about Calc).

Once one's using variables, it will probably be necessary to wrap the
final calculation in evalv() to get a numeric value as output instead of
a formula with the variable names in it.

Another obstacle to what Ypo is trying to do is the attempt to use the $
sign for the currency unit. Calc does not have pre-defined currency
units, and $ is taken - it refers to the last value on stack. I tend to
use 'USD'.

So a partial, if pointless, way to do this would be to first store the
variables with the calculator:

  ' 300 m
    s s a       # store a = 300 m
  ' 300 m
    s s b       # store b = 300 m
  ' 1 USD/m^2
    s s cost    # store cost = (1) usd/m^2
  ' a*b
    s s Area    # store Area = a*b (*not* 90000 m^2)

Then the last step could be done in a src block:

  #+begin_src calc
    evalv(Area * cost)
  #+end_src

  #+RESULTS:
  : 90000 USD

(Another cool bit: If you change the value of a or b and rerun the src
block, the result will change, since what was stored in Area was the
product of the variables, not the product of their values.)

Yours,
Christian