delta forth

7/31/2019 Delta Forth

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Worlds first Forth compiler for the .NET platformValer BOCAN, PhD


2/22

What is Forth anyway?

Reverse Polish Notation Stack-based programming

Delta Forth .NET

Demonstration


3/22

Procedural, stack-based language that iscompiled and interpreted at the same time

Developed by Chuck Moore at the US NationalRadio Astronomy Observatory in the early 1970s

Procedures are called words that are grouped in

vocabularies.

Forth is a meta-language, as new words can formnew specialized Forth-like languages


4/22

Popular for developing embedded systems.

Implemented on RISC processors Open Firmware boot ROMs used by Apple, IBM,

and Sun Microsystems

First stage boot controller for FreeBSD

Software that controlled the robotic arm thatrepaired the Hubble Space Telescope


5/22

50-70% of a typical Forth implementation iswritten in Forth

Implementation effort is small; a singledeveloper can create a Forth system on a newplatform in months

Delta Forth .NET was implemented in just 5weeks


6/22


Reverse Polish Notation Stack-based programming

Delta Forth .NET

Demonstration


7/22

Invented by Charles Hamblin in 1950s to enablezero-address memory stores

In postfix notation, the operators follow theiroperands, i.e. 3 + 5 becomes 3 5 +

RPN obviates the needs for parentheses

otherwise required by infix notation

Reading from left to right, calculations can occuras soon as an operator is read


8/22

2

5

+

7

10

4

-

*

6

42

Take infix expression (2 + 5) * (10 4)

This translates to postfix expression 2 5 + 10 4 - *

See how the postfix expression is evaluated usinga stack-based algorithm


9/22


Reverse Polish Notation

Stack-based programming

Delta Forth .NET

Demonstration


10/22

Unusual programming style, close to machine

Forth uses two stacks:

Parameter stack, used to transmit parametersbetween words

Return stack, used to hold the return address of the

word caller and some counter for loop functions There are some powerful primitives to handle the

stacks


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DUP duplicates the topmost element on thestack

33

20

9

33

33

20

9


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DROP drops the topmost element on the stack

33

20

9

20

9


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SWAP swaps the two topmost elements on thestack

33

20

9

20

33

9


14/22

OVER duplicates the second topmost elementon the stack

33

20

9

20

33

20

9


15/22

ROT rotates the three topmost elements on thestack

33

20

9

33

20

10

9

10


16/22


Reverse Polish Notation

Stack-based programming

Delta Forth .NET

Demonstration


17/22

Sequel of the Delta Forth for Java project (1997)

C# command-driven application

This dialect is not interpreted, the generatedcode is fully managed

Supports Forth at the .NET consumer level (i.e.no new .NET classes can be derived)

Supports interoperability with other .NETlibraries


18/22

Perhaps the most odd looking Hello World outthere

: main \ Entry point

."Hello World"

;


19/22

Finding prime numbers (up to 400 in this case)

400 constant limit

: isprime \ Returns 1 if the

number on top of stack is a prime

number

2

begin

over over mod 0= 0=

rot rot dup >r

over 2 / > 0=

rot and r> swap

while

1+

repeat

over 2 / >

;

: main \ Entry point

."Prime numbers up to " limit . .":"

limit 1 do

i isprime

if i . space then

loop

;


20/22

Euclids algorithm4330 constant num1 \ The first number

8235 constant num2 \ The second number

( Word to test if value on top of stack is equal to

or less than 0 )

: ZeroLessEqual

dup 0=

swap 0

delta forth

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