Lisp Emulator - Version 1.0.3

Intro

Lisp is a functional programming language, first introduced in the late 1950s by John McCarthy, a renowned computer scientist. Since then, many dialects of Lisp have been developed, with Common Lisp and Scheme being the main dialects nowadays.

Lisp is written in a prefix notation, and the code is always inside parenthesis. It is also not case sensitive, however feel free to follow the most updated conventions .

The project focuses on emulating a basic environment resembling Common Lisp syntax and other compatible older versions. All of the code is3 written in Python.

Installation

You can install the project from pip via the following command:

pip install lisp-emulator

Usage

First, you need to import the library:

from lisp_emulator.common_lisp import *

You can evaluate a lisp expression using the eval_lisp command.

result = eval_lisp("( + 3 2 )")
print(result) # 5

Lisp-Like Syntax

As mentioned, the supported syntax is similar to lisp, and more specifically to the Common Lisp dialect. In this section of the documentation, we'll dive in into the different supported features in this special syntax.

Arithmetic Operators

The most fundamental operations are addition (+), subtraction (-), multiplication(*) and division (/). Those operators are of course supported and can receive an unlimited number of parameters.

Pay attention that those are not binary operations as we're used to in math and other programming languages. This is because in Lisp we use a prefix notation.

Here are some examples of basic calculations:

    (+ 5 6 8)   ; 19
    (- 8 2 1)   ; 5
    (+ 6 4 (- 5 2))   ; 13
    (* 7 3)   ; 21
    (/ 6 2)   ; 3

Output

You can use the PRINT or WRITE commands. For example:

( print "hello" )
"HELLO"

Predicates

Predicates return a boolean-like value - T (for true), and NIL (the equivalent of false).

• ZEROP - evaluates to T if the number is 0, else to NIL
• EVENP - evaluates to T if the number is odd, else to NIL
• ODDP - evaluates to T if the number is even, else to NIL
• LESSP - evaluates to T if the first value is smaller than the other
• GREATERP - evaluates to T if the first value is bigger than the other
• NUMBERP - evaluates to T if the value is a number, else to NIL
• STRINGP - evaluates to T if the value is a string (by the double quotation ".." mark), else to NIL

Equality Operation

Equality can be performed via the = operator that can receive an indefinite number of parameters or the EQ method that receives only 2 parameters. Those methods return T if all the expressions are equal, else NIL.

Mathematical Operations And Constants

PI Constant - PI is a global constant, and represents approximately 3.1415926535. E Constant - E is a global constant, and represents approximately 2.71828182846.

Trigonometric operations

All of the trignonometric operations are handled in radians, rather than degrees. Here is a full list of the supported trigonometric functions;

• SIN - receives a parameter and returns its sine.
• COS - receives a parameter and returns its cosine
• TAN- receives a parameter and returns its tangent
• ASIN - The reverse operation of SIN. receives a parameter within range of -1 and 1 and returns the angle that its sine equals to the parameter (in radians)
• ACOS - The reverse operation of COS. receives a parameter within range of -1 and 1 and returns the angle that its cosine equals to the parameter (in radians)
• ATAN- The reverse operation of TAN. receives a parameter within range of -1 and 1 and returns the angle that the result of its tangent operation equals to the parameter (in radians)
• SINH - Hyperbolic sine
• COSH - Hyperbolic cosine
• TANH - Hyperbolic tangent
• ASINH - The reverse operation of SINH
• ACOSH - The reverse operation of COSH
• ATANH - The reverse operation of TANH

For instance:

( sin ( / PI 2 ) ) ; 1.0

Other mathematical operations

• SQRT - receives a parameter and returns its square root
• EXPT - receives two parameters and returns the power of the first parameter by the second.
• EXP - receives one parameter and returns the power of E ( 2.71828182846 ) by that number.
• MAX - receives N parameters and return the value of the biggest.
• MIN - receives N parameters and return the value of the smallest.
• GCD - receives N parameters and returns their Greatest Common Denominator Operation.
• ABS - receives a parameter, and returns its absolute value.

Creating Variables

You can define new variables via the SET and SETQ methods ( defvar, defparameter keywords are not implemented yet )

For example:

( setq number 5 ) ; 5
( + 3 number 4 ) ; 12

Conditionals

Conditions are created via IF expressions

String Operations

Concatenate - receives N strings and evaluates to their concatenation. For example,

Data Types

There are currently only 3 supported datatypes in the project: strings, integers and decimals. str - strings. A sequence of characters, sorrounded by double quotes. For example: "hello" , "world". int - integers. For example: 6, -3 ,2. dec - decimal numbers. For instance, 6.1, 2.23, etc...

Predicates

Predicates return a boolean-like value - T (for true) , and NIL (the equivalent of false).

• ZEROP - evaluates to T if the number is 0, else to NIL
• EVENP - evaluates to T if the number is odd, else to NIL
• ODDP - evaluates to T if the number is even, else to NIL
• LESSP - evaluates to T if the first value is smaller than the other
• GREATERP - evaluates to T if the first value is bigger than the other
• NUMBERP - evaluates to T if the value is a number, else to NIL
• STRINGP - evaluates to T if the value is string (by the double quotation ".." mark) else, to NIL

Equality Operation

Equality can be performed via the = operator that can receive an indefinite number of parameters or the EQ method that receives only 2 parameters. Those methods return T if all the expressions are equal, else NIL.

Constants

You can use these global constants anywhere in your program.

• PI Constant - PI is a global constant, and represents approximately 3.1415926535.
• E Constant - E is a global constant, and represents approximately 2.71828182846.