The ' character, pronounced "tick", returns the execution token of the next word in the input stream.
ETs are the address of a word's executable code. Other fetch and store c! \ fetch/store a single ! \ fetch/store one 2! \ fetch/store two f! \ fetch/store a floating point valueįorth also has "value", which is a construct similar to other languages' "reference":ġ0 value myval \ create a new word that returns the value 10Ģ0 to myval \ Changes myval to return 20 instead of 10įorth also has a concept analogous to function pointers - the "execution token". \ prints the value stored in myvarġ myvar +! \ add 1 to the value stored in myvar This address may be accessed with (fetch) or ! (store): This creates the word "myvar", which when executed leaves the address of a cell of memory on the stack. To declare a variable that lives in memory:įvariable myfvar \ stores 1 floating point number (often 8 bytes) Address alignment requirements depend on the processor being used to host the Forth system. Cells are the native word size of the host processor, and are usually either 16 or 32 bits in size. In Forth, memory is addressable in characters, cells and double cells. ( define B ( box 42 )) → B box reference ( unbox B ) → 42 box contents sets new value for box contents ( define ( change-by-ref abox avalue ) ( set-box! abox avalue ) ) ( change-by-ref B 666 ) → # ( unbox B ) → 666 Forth įorth is an untyped language, and treats pointers in much the same way that assembly language does. It uses what is called "Motorola syntax" where an immediate value needs a # in front, or else the number is interpreted as a pointer to memory. When you have a statement like int x = 3 in a language like C or mov eax,3 in X86 Assembly, the 3 in both cases is called a constant or immediate value, meaning that the value 3 is what gets stored. 43.2 Addresses of variables or procedureĦ502 Assembly is different from most other assembly languages, in the way constants are specified.
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