How to resolve the algorithm Topic variable step by step in the PicoLisp programming language

Published on 12 May 2024 09:40 PM
#Picolisp

How to resolve the algorithm Topic variable step by step in the PicoLisp programming language

Table of Contents

Problem Statement

Several programming languages offer syntax shortcuts to deal with the notion of "current" or "topic" variable. A topic variable is a special variable with a very short name which can also often be omitted. Demonstrate the utilization and behaviour of the topic variable within the language and explain or demonstrate how the topic variable behaves under different levels of nesting or scope, if this applies, within the language. For instance you can (but you don't have to) show how the topic variable can be used by assigning the number

3

{\displaystyle 3}

to it and then computing its square and square root.

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Topic variable step by step in the PicoLisp programming language

Source code in the picolisp programming language

PicoLisp sets the value of the variable (symbol) '@' to the result of
conditional and controlling expressions in flow- and logic-functions (cond, if,
and, when, while, etc.).

Within a function or method '@' behaves like a local variable, i.e. its value is
automatically saved upon function entry and restored at exit.

For example, to read the current input channel until EOF, and print the square
of every item which is a number:

(while (read)
   (when (num? @)
      (println (* @ @)) ) )
abc   # Not a number
7     # Number
49    # -> print square
xyz   # Not a number
3     # Number
9     # -> print square

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