9.3.40: `rpnfunction'

`rpnfunction name replacement-words'

Create a new keyword for use in rpn expressions. Inside any RPN expression which follows this line, the word `name' will be substituted with the indicated replacement words.

For example, the following shows the definition and use of a function which computes the sine of twice an angle, by multiplying whatever is on the stack by `2', and then taking the sine of the result.

rpnfunction sin2 2 * sin show "expect the number 1 to follow: " {rpn 45 sin2}

The replacement words will have any synonyms in them translated first, unless they start with an underscore followed by a double backslash. Similarly, variables are substituted unless they start with an underscore. These exceptions are to allow the use of the `defined' operator (see rpn Mathematics).

Note: The mathematical constants `e' and `pi' are stored using `rpnfunctions'. Also, two `rpnfunctions' are provided for finding the slope and intercept of a line joining two points, e.g.

# Expect answers 1 and 10 ... show "slope=" {rpn 0 1 1 11 linear_slope} show "inter=" {rpn 0 1 1 11 linear_intercept}

These are useful in `set grid missing above .intercept. .slope.' and `set z missing above .intercept. .slope.'.