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World’s first Forth compiler for the.NET platform Valer BOCAN, PhD

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What is Forth anyway? Reverse Polish Notation Stack-based programming Delta Forth.NET Demonstration

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Procedural, stack-based language that is compiled and interpreted at the same time Developed by Chuck Moore at the US National Radio Astronomy Observatory in the early 1970s Procedures are called words that are grouped in vocabularies. Forth is a meta-language, as new words can form new specialized Forth-like languages

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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 that repaired the Hubble Space Telescope

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50-70% of a typical Forth implementation is written in… Forth Implementation effort is small; a single developer can create a Forth system on a new platform in months Delta Forth.NET was implemented in just 5 weeks

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What is Forth anyway? Reverse Polish Notation Stack-based programming Delta Forth.NET Demonstration

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Invented by Charles Hamblin in 1950’s to enable zero-address memory stores In postfix notation, the operators follow their operands, 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 occur as soon as an operator is read

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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 using a stack-based algorithm

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What is Forth anyway? Reverse Polish Notation Stack-based programming Delta Forth.NET Demonstration

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Unusual programming style, close to machine Forth uses two stacks: Parameter stack, used to transmit parameters between 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 the stack 33 20 9 33 20 9

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DROP – drops the topmost element on the stack 33 20 9 9

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SWAP – swaps the two topmost elements on the stack 33 20 9 33 9

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OVER – duplicates the second topmost element on the stack 33 20 9 33 20 9

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ROT – rotates the three topmost elements on the stack 33 20 9 33 20 10 9

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What is Forth anyway? Reverse Polish Notation Stack-based programming Delta Forth.NET Demonstration

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Sequel of the Delta Forth for Java project (1997) C# command-driven application This dialect is not interpreted, the generated code is fully managed Supports Forth at the.NET consumer level (i.e. no new.NET classes can be derived) Supports interoperability with other.NET libraries

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Perhaps the most odd looking Hello World out there : main\ Entry point."Hello World" ; : main\ Entry point."Hello World" ;

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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 ; 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 ;

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Euclid’s algorithm 4330 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< or ; : gcd(num1 num2 - - -) over ZeroLessEqual if(num1 is <= 0) drop drop else dup ZeroLessEqual if(num2 is <= 0) drop drop else begin over over = if(We've got the result). else over over > if swap then over - 0 then until then ; : main\ Entry point."GCD of " num1.." and " num2.." is " num1 num2 gcd cr ; 4330 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< or ; : gcd(num1 num2 - - -) over ZeroLessEqual if(num1 is <= 0) drop drop else dup ZeroLessEqual if(num2 is <= 0) drop drop else begin over over = if(We've got the result). else over over > if swap then over - 0 then until then ; : main\ Entry point."GCD of " num1.." and " num2.." is " num1 num2 gcd cr ;

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What is Forth anyway? Reverse Polish Notation Stack-based programming Delta Forth.NET Demonstration

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www.bocan.ro/deltaforthnetvaler@bocan.ro

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