>

> I haven't used FORTH in a while, but am constantly using my HP

> 15C and HP35 calculators, both of which operate very in a FORTH manner.

> FORTH and RPN calculators really DO make sense... You give the machine

> the numbers, then tell it what to do with them. This is also called post

> fix notation, as opposed to the in fix notation we're more familiar with.

> Consider a typical calculator's keystrokes...

>

> 2 first argument

> + I can't add anything yet!

> 3 second argument

> = ok, I remember, he wanted to add!

>

> On an HP (or FORTH), this would be something like

>

> 2 first argument, put on stack

> 3 second argument, put on stack

> + Replace two arguments on stack with one result

> of sum, display

>

> Also, most calculators that use algebraic notation often use a

> mix of RPN and algebraic when they have single argument functions:

>

> 2 function argument

> sqrt do the square root of it

>

> This mix of in-fix and post-fix on algebraic calculators can make

> it fun figuring out which to use when (along with hitting the equals key

> a half dozen times). With RPN, the calculation proceeds the way you

> would do it by hand (from the inner most parentheses on out).

>

> FORTH is an interesting language, though it tends to be write

> only (no one else can read it). I've seen some neat algorithms that

> convert algebraic expressions to FORTH, which can then be easily

> evaluated by a stack oriented machine.

> Finally, years and years ago I licensed a 6800 Basic interpreter

> from Microsoft. It's interesting to see how it evaluates an expression.

> It actually scans the line left to right, interpreting as it goes along.

> When it sees some sort of two argument operator (like + ), it goes on and

> evaluates the second argument, which may involve recursive function

> calls. It's pretty neat. When it finds a function call, it calls the

> function evaluator, which then looks at the argument and calls the

> function evaluator again to evaluate the argument to the function. This

> continues until there is actually some number that is returned, then all

> the functions return.

>

> So... so much for Forth, RPN, and algebra!

>

> Harold

>

> Harold Hallikainen

>

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