SCI Programming Language/Introduction

Official SCI Documentation

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Introduction to the SCI Language
Author: Jeff Stephenson

 

The SCI language is an object-oriented language with a Lisp-like syntax. It is compiled by the sc compiler into p-machine code which is used by the interpreter, sci.exe. We will begin our discussion of the language with its basic Lisp-like characteristics, then go on to the object-oriented parts of the language. Like Lisp, SCI is based on parenthesized expressions which return values. An expression is of the form:

(procedure [parameter parameter...])

The parameters to a procedure may themselves be expressions to be evaluated, and may be nested until you lose track of the parentheses. Unlike Lisp, a procedure itself may not be the result of an evaluation. An example of an expression is:

(+ (-y 2) (/ x 3))

which would be written in infix notation as:

(y -2) + (x / 3)

All expressions are guaranteed to be evaluated from left to right. Thus,

(= x 4) (= y (/ (+= x 4) ( / = x 2)))

will result in y = 2 and x = 4.

Comments in SCI begin with a semicolon and continue to the end of the line.

Primitive Procedures

Arithmetic primitives

In the following examples, e1, e2, etc. are arbitrary expressions. Brackets [...] indicate optional entries. Procedures evaluate their parameters from left to right.

Addition

(+ e1 e2 [e3...])

evaluates to: e1 + e2 [+ e3...]

example: (+ 7 12 4) evaluates to 23.

Multiplication

(* e1 e2 [e3...])

evaluates to: e1 (*e2[*e3...]

example: (* 2 10 3) evaluates to 60.

Subtraction

(- e1 e2)

evaluates to : e1 - e2

example: (- 20 11) evaluates to 9.

Division

(/ e1 e2)

evaluates to: e1 / e2

example: (/ 24 6) evaluates to 4. <---- Note: does this round when necessary (up, down)?

Remainder

(mod e1 e2)

evaluates to: the remainder of e1 when divided by e2.

example: (mod 17 5) evaluates to 2.

Operation Shift Left

(<< e1 e2)

evaluates to : e1<< e2 where the << operation shifts its left hand side left by the number of bits specified by its right hand side.

example: (<< 7 2 ) evaluates to 28.

In binary: 111 << 2 = 11100

Operation Shift Right

(>> e1 e2)

evaluates to: e1 >> e2 (as in << except with a right shift)

example: (>> 7 2) evaluates to 1.

In binary: 111 >> 2 = 001

Bitwise Exclusive OR Operator

(^ e1 e2 [e3...])

evaluates to: e1^ e2 [^ e3...]

example: (^ 11 26) evaluates to 17.

In binary: 01011" 11010 = 10001

Bitwise AND Operator

(& e1 e2 [e3...])

evaluates to: e1 &e2 [& e3...]

example:

(& 11 26) evaluates to 10.

In binary: 01011 & 11010 = 01010

Bitwise OR Operator

(| e1 e2 [e3...])

evaluates to: e1 | e2 [| e3...]

example: (| 11 26) evaluates to 27.

In binary: 01011 111010 = 11011

Bitwise NOT

(~ e1)

evaluates to: the bitwise not of e1 (all 1 bits are changed to 0 and all 0 bits are changed to 1).

example: (~ 11) evaluates to -12.

In binary: ~01011 = 1111111111110100 (all the leading 0s in the 16 bit number change to 1s).

 

Notes

 

Table of Contents

 

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