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8/8/2019 Forth Family[1]

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Forth Language FamilyForth Language FamilyComputer Science Department

Arkansas State University

Computer Science Department

Arkansas State University


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Forth

Chuck Moore, late 1960s

postfix notation, stack-based

simple type system, low-level

threaded execution, VM and native

compact, interactive, extendableenvironment

bottom-up programming


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Forth

Standardized:

FIG-Forth, Forth-77, Forth-79, Forth-83, ANSI-

Forth (94)

Environment:

compiler, editor, assembler, (disassembler,

decompiler,) file/disk manager, dictionary

pforth: http://www.softsynth.com/pforth/

gforth:

http://www.complang.tuwien.ac.at/forth/gforth/


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Forth Examples

: STAR [CHAR] * EMIT ;

: STARS 0 DO STAR LOOP CR ;

: SQUARE DUP 0 DO DUP STARS LOOP

DROP ;

: TRIANGLE 1 DO I STARS LOOP ;

: TOWER ( n -- ) DUP TRIANGLE SQUARE ;


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Forth Examples

: STAR ( -- ) \ Print a single star

42 EMIT ; \ 42 is the ASCII code for *

: STARS ( n -- ) \ Print n stars

0 DO STAR LOOP ; \ Loop n times (0 up to n-1) and execute STAR

: SQUARE ( n -- ) \ Print an n-line square of stars

DUP 0 DO \ Loop n times, keeping (DUP-licating) n on the

stack

DUP STARS CR \ Each time, print n stars then print CR

LOOP DROP ; \ After loop is done, drop the n from the stack

: TRIANGLE ( n -- ) \ Print an n-line triangle

1 + 1 DO \ Loop n times from 1 to n (instead of 0 to n-1)

I STARS CR \ This time use the inner loop index I

LOOP ;

: TOWER ( n -- ) \ Print a "tower" with an base of size n


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Forth Examples

CR 7 STARS \ user types this line, output follows

******* ok

CR 3 TRIANGLE \ user types this line, output follows

*

**

***

ok

CR 6 TOWER \ user types this line, output follows

*

**

***

****

*****

******

******

******

******


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Forth Examples \ fib ( x -- , returns first x numbers in Fibonacci sequence )

: fib { x -- } \ local index variable x

1 dup . \ initialize sequence & print initial

values

1 dup .

begin

over over + \ add previous 2 numbers in sequence

dup . rot drop \ add new number to stack, drop bottomnumber

x 1- dup -> x 3 < \ decrement x, exit if x < 3

until

drop drop \ drop top 2 elements off stack

;


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Postscript

Created by Adobe

Used as language for vector-based

graphics programming

Current version 3.0

ghostscript:

http://pages.cs.wisc.edu/~ghost/


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Postscript Example %!PS-Adobe-3.0

/inch {72 mul} def

/Times-Roman findfont 50

scalefont setfont

2.5 inch 5 inch moveto

(Hello, World!) show

showpage


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Joy

website:

http://www.latrobe.edu.au/philosophy/phimvt/joy.html

stack-based

purely functionalconcatenative

uses quotation and combinators


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Joy Example

DEFINE square == dup * ; cube == dup dup * * .

DEFINE factorial ==[0 =] [pop 1] [dup 1 -

factorial *] ifte .


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Factor

website: http://factorcode.org/dynamic typing

object system

garbage collection

reflection


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Factor Examples USE: io

IN: hello-world

: hello ( --

) "Hello world" print ;

MAIN: hello


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Factor Examples

! Copyright (C) 2008 Slava Pestov.

! See http://factorcode.org/license.txt for BSD license.

USING: accessors calendar calendar.format io io.encodings.ascii

io.servers kernel threads ;

IN: time-server

: handle-time-client ( -- )

now timestamp>rfc822 print ;

: ( -- threaded-server )

ascii

"time-server" >>name

1234 >>insecure

[ handle-time-client ] >>handler ;

: start-time-server ( -- )

start-server drop ;

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