64 lines
2.9 KiB
Plaintext
64 lines
2.9 KiB
Plaintext
Stack notation: "<stack before> -- <stack after>". Rightmost is top of stack
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(TOS). For example, in "a b -- c d", b is TOS before, d is TOS after. "R:" means
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that the Return Stack is modified.
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DOES>: Used inside a colon definition that itself uses CREATE, DOES> transforms
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that newly created word into a "does cell", that is, a regular cell ( when
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called, puts the cell's addr on PS), but right after that, it executes words
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that appear after the DOES>.
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"does cells" always allocate 4 bytes (2 for the cell, 2 for the DOES> link) and
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there is no need for ALLOT in colon definition.
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At compile time, colon definition stops processing words when reaching the
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DOES>.
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Example: ": CONSTANT CREATE HERE @ ! DOES> @ ;"
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Word references (wordref): When we say we have a "word reference", it's a
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pointer to a words *code link*. For example, the label "PLUS:" in this unit is a
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word reference. Why not refer to the beginning of the word struct? Because we
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actually seldom refer to the name and prev link, except during compilation, so
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defining "word reference" this way makes the code easier to understand.
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Atom: A word of the type compiledWord contains, in its PF, a list of what we
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call "atoms". Those atoms are most of the time word references, but they can
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also be references to NUMBER and LIT.
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*** Native Words ***
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: x ... -- Define a new word
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; R:I -- Exit a colon definition
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. n -- Print n in its decimal form
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@ a -- n Set n to value at address a
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! n a -- Store n in address a
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+ a b -- c a + b -> c
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- a b -- c a - b -> c
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* a b -- c a * b -> c
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/ a b -- c a / b -> c
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CREATE x -- Create cell named x. Doesn't allocate a PF.
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CURRENT -- n Set n to wordref of last added entry.
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DOES> -- See description at top of file
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DUP a -- a a
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ELSE -- Branch to THEN
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EMIT c -- Spit char c to stdout
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EXECUTE a -- Execute wordref at addr a
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HERE -- a Push HERE's address
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IF n -- Branch to ELSE or THEN if n is zero
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QUIT R:drop -- Return to interpreter promp immediately
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KEY -- c Get char c from stdin
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INTERPRET -- Get a line from stdin, compile it in tmp memory,
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then execute the compiled contents.
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OVER a b -- a b a
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SWAP a b -- b a
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THEN -- Does nothing. Serves as a branching merker for IF
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and ELSE.
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*** Core-but-Forth Words ***
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? a -- Print value of addr a
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+! n a -- Increase value of addr a by n
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ALLOT n -- Move HERE by n bytes
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CONSTANT x n -- Creates cell x that when called pushes its value
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VARIABLE c -- Creates cell x with 2 bytes allocation.
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