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| 3. Memory management. Memory does not understand what you want to put in it. CPUs do not understand STRINGS. Strings are conventions. A 'string' of bytes terminated by a zero has no intrinsic meaning to a CPU. It's your convention. You have to keep track of it, by convention. The zero at the end isn't enough to associate a string with a label (also, itself, a string). ultimately you need a table for this (or a dictionary). Some data structure by convention. At that means, certain regions of memory will be marked OPEN or CLOSED -- FREE or USED -- and dealt with accordingly. | 3. Memory management. Memory does not understand what you want to put in it. CPUs do not understand STRINGS. Strings are conventions. A 'string' of bytes terminated by a zero has no intrinsic meaning to a CPU. It's your convention. You have to keep track of it, by convention. The zero at the end isn't enough to associate a string with a label (also, itself, a string). ultimately you need a table for this (or a dictionary). Some data structure by convention. At that means, certain regions of memory will be marked OPEN or CLOSED -- FREE or USED -- and dealt with accordingly. |
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| More to come! | == Tying it all together |
| | Known as "threading". Forth changed how I thought about languages because of it's innovative use of a dictionary structure. BASIC and Python, in contrast, are interpreted languages. You sit there and write a parser for the //text//, to then run commands by calling a function inside the interpreter. Ultimately, you have created a state machine and are interpreting commands which modify that state machine. If it's just "commands" it might be like a script or a macro language. But most languages like BASIC or Python are really state machines. They maintain lists of variables. They have expression parsers, and so forth. |
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| | Forth on the other hand, has a "dictionary" of words that are "chained" together. This means adding a new world is trivial, it just chains it to the end of the dictionary like a linked list. And how does it "compile" these "words"? Simple. It writes CALL functions to the addresses of native words. A set of such CALLs is a function definition (written out of other Forth words). This is called "subroutine threaded compilation". You can also inline some functions by directly copying the function into the binary versus writing a CALL to the runtime. In that sense, Forth is a kind of bytecode-- but one in which you can add your own bytes to the code. Forth itself is a state machine as well, since it maintains its stacks, the depth of them, and maintains a dictionary. The native words in the dictionary are part of it's initial state. The construction of the apparatus which holds them is also known as a 'state', in terms of a 'state machine'. |
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| | So we see, that in the design and construction of a programming language, what is very important is the 'state machine' you have chosen to adopt, or rather, the state machine you have chosen to replace the CPU. So you don't have to actually understand the CPU. |
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| | //More soon!// |
