~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~ ~~ Code transformation facility ~~ ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~ ~ TODO explain what problem this is solving and why ~ ~ The label transform operates on code that compiles itself, and ensures ~ that the result of the compilation is suitable to be included in an ~ executable binary. To achieve this, it makes several changes to the ~ semantics of that code. The transform relies on the label facility, and ~ expects to run from within label-loop. ~ ~ The most fundamental change is that the label transform separates words ~ that run in compile mode from words that run immediately. There is no ~ distinction made between words running in immediate mode, and words declared ~ as immediate. Immediate words are looked up and executed based on their ~ "real", currently-executing definitions. Compiled words, including ~ literals, are looked up via the label facility. ~ ~ Since the label facility is able to resolve forward references, there is ~ no hard requirement that everything in the file be topologically sorted. ~ However, the transform will refuse to create forward references to compiled ~ words. If you want them, you can create them by hand by calling use-label ~ yourself. This restriction is in place because allowing forward references ~ would be a significant difference from un-transformed code that could easily ~ become confusing, and because it simplifies the implementation a bit. ~ ~ Compilation words do make extensive reference to the global variables ~ "here" and "latest". In particular, flow-control words such as if-else ~ expect the log to have recent compilation outputs on it, and to be able to ~ mutate them in-place. In order to make this work, we provide temporary ~ values of these two variables which point to the location of the output ~ buffer. This allows pointer resolution to work correctly without additional ~ effort, but notice that the buffer's address will differ from the address ~ the resulting program loads itself at. There's no simple way to avoid this ~ concern, since the variables must point to one of those addresses or the ~ other, not both. ~ ~ We resolve the issue by running our own, alternate versions of the words ~ "create", ":", ";", and ";asm" which use the label facility to compute the ~ addresses that will be needed at runtime. These alternates run instead of ~ the normal versions of these words. The code being compiled is responsible ~ for not doing anything else that would rely on "here" and "latest" matching ~ their runtime addresses, though it is otherwise allowed to modify and rely ~ on them in all the usual ways. The alternate versions are defined in this ~ file as their own words, "Lcreate", "L:", "L;", and "L;asm". ~ ~ Note that these alternates are applied via a purely lexical ~ transformation: when a word would be looked up in the dictionary to ~ interpret, first check if it's one of these. That means the transformation ~ won't apply to indirect callers of these words, nor to tick-quotes of them. ~ The code being compiled is responsible for not doing either of those things. ~ ~ Notably, the transformation uses the same "interpreter-flags" variable as ~ the rest of Evocation. There's no need to keep it separate like there is ~ with the other variables. This makes it easy to change modes. ~ ~ The transformation and the alternates rely on various labels, all of which ~ must be defined elsewhere, lest the label loop fail to converge: "lit", ~ "origin", "docol", "exit", ":", ";", and ";asm". ~ ~ All of these limitations result in the compiled code being, in effect, ~ written in a dialect which is like Evocation, but more restricted. This is ~ acceptable, because the label transform is intended for compiling code that ~ is an early part of Evocation itself, and the necessary code has all been ~ written to follow these restrictions. ~ TODO all this buffer stuff should be in its own file ~ (buffer size -- buffer address) : read-to-buffer dup allocate dup dup ~ (buffer size, buffer address, word start, output point) { key ~ Exit if it's a zero byte. dup not { ~ Make sure to pack the zero to serve as a null terminator. pack8 drop drop swap drop exit } if dup is-space { ~ (buffer size, buffer address, word start, output point, key) ~ Tuck the key out of the way until we've done some stuff. 3unroll ~ If it's a space character, first check if we just consumed the magic ~ word... 2dup swap - 8 = dup { drop ~ Add a null terminator so we can use stringcmp dup 0 swap ! ~ Check for the magic word over s" pyrzqxgl" stringcmp 0 = } if { ~ It's magic, so exit. ~ Make sure to pack a zero to serve as a null terminator. 0 pack8 drop drop drop swap drop exit } { ~ It's not magic, so reset the word start. Of course whitespace is ~ not a word but this will help us keep track of things. 3roll pack8 swap drop dup } if-else } { ~ (buffer size, buffer address, word start, output point, key) ~ Tuck the key out of the way again. 3unroll ~ Check if the word just started and the previous character is space. 2dup = dup { drop dup @ is-space } if { ~ If so, this is the actual first character of the word. drop swap pack8 dup } { ~ If not, leave the word start alone. 3roll pack8 } if-else } if-else } forever ; ~ In logical terms, this modifies an input buffer metadata structure ~ in-place to push a new, zeroed one into the start of the linked list formed ~ through the next-source field. ~ ~ In physical terms, it works by allocating a new structure, copying the ~ fields of the existing one into it, and zeroing the existing one. That's ~ necessary because otherwise we'd need a mutable handle (a pointer to a ~ pointer) to update the start of the list, and there's no way to do that with ~ the main-input-buffer variable working the way it presently does. ~ ~ (input buffer metadata pointer --) : push-input-buffer allocate-input-buffer-metadata ~ (original metadata pointer, new metadata pointer) 2dup swap 6 8 * memcopy ~ (original metadata pointer, new metadata pointer) swap dup zero-input-buffer-metadata input-buffer-next-source ! ; ~ This does the inverse of push-input-buffer. In the event that the ~ next-source field is null, it zeroes the buffer. ~ ~ Note, however, that it doesn't deallocate the memory, because that's not ~ how memory allocation on the log works. If necessary, it can be deallocated ~ with "forget", though as usual that requires careful planning. ~ ~ (input buffer metadata pointer --) : pop-input-buffer dup input-buffer-next-source @ ~ (original metadata pointer, next source metadata pointer) dup { 6 8 * memcopy } { drop zero-input-buffer-metadata } if-else ; : transform-state-saved-here ; : transform-state-saved-latest 8 + ; : transform-state-output-buffer-start 2 8 * + ; : allocate-transform-state 3 8 * allocate dup transform-state-saved-here 0 swap ! dup transform-state-saved-latest 0 swap ! dup transform-state-output-buffer-start 0 swap ! ; allocate-transform-state s" transform-state" variable ~ When calling the label facility during a transformation, it's necessary ~ to use the real, non-wrapped "heap" and "latest". : swap-transform-variables here @ transform-state transform-state-saved-here @ here ! transform-state transform-state-saved-here ! latest @ transform-state transform-state-saved-latest @ latest ! transform-state transform-state-saved-latest ! ; ~ (address within the output buffer -- address at generated binary's runtime) : transform-offset ~ Don't transform null pointers. dup { transform-state transform-state-output-buffer-start @ - swap-transform-variables L@' origin swap-transform-variables + } if ; ~ This is the alternate version of "create" for use with the label ~ transform. Its code is the same as the regular "create" except as noted ~ below. It is likely to be extremely useful to read and understand "create" ~ in interpret.e before attempting to understand "Lcreate". : Lcreate dup stringlen 1 + dup 3unroll here @ 10 + 3unroll memmove here @ ~ This value of "latest" is going into the generated output, so call ~ transform-offset on it first. latest @ transform-offset pack64 0 pack8 0 pack8 + 8 packalign here @ latest ! ~ Now we're immediately after the word header, which is where the codeword ~ will be. This is the value the label should taken on, so we set it. dup here @ 10 + swap-transform-variables intern-label set-label swap-transform-variables here ! ; ~ This is the alternate version of ":" for use with the label transform. Its ~ code is the same as the regular "create" except as noted below. It is likely ~ to be extremely useful to read and understand ":" in interpret.e before ~ attempting to understand "L:". : L: ~ This calls "Lcreate" instead of "create". word value@ Lcreate dropstring ~ This looks up "docol" by label. swap-transform-variables L@' docol L@' origin swap-transform-variables + , latest @ hide-entry ] ; ~ This is the alternate version of ";" for use with the label transform. Its ~ code is the same as the regular "create" except as noted below. It is likely ~ to be extremely useful to read and understand ";" in interpret.e before ~ attempting to understand "L;". : L; ~ This looks up "exit" by label. swap-transform-variables L@' exit L@' origin swap-transform-variables + , latest @ unhide-entry ~ Since [ is an immediate word, we have to go to extra trouble to compile ~ it as part of ;. [ ' [ entry-to-execution-token , ] ; make-immediate ~ This is the alternate version of ";asm" for use with the label transform. ~ Its code is the same as the regular "create" except as noted below. It is ~ likely to be extremely useful to read and understand ";asm" in interpret.e ~ before attempting to understand "L;asm". : L;asm here @ pack-next 8 packalign here ! latest @ dup unhide-entry entry-to-execution-token dup 8 + swap ! ~ Since [ is an immediate word, we have to go to extra trouble to compile ~ it as part of ;asm. [ ' [ entry-to-execution-token , ] ; make-immediate ~ This implements the label transform for a single word. It is directly ~ analogous to "interpret", and reading interpret.e may help in understanding ~ it, though it's meant to still make sense on its own. ~ ~ It expects to be called from "transform", below, which loops. ~ ~ (-- done) : transform-one word ~ If no word was returned, exit. dup 0 = { drop 0 exit } if ~ The string is on the top of the stack, so to get a pointer to it we get ~ the stack address. ~ (string) value@ ~ If it's the magic word, end the transformation. dup s" pyrzqxgl" stringcmp 0 = { drop dropstring 1 exit } if ~ Check whether it's one of the words we have alternates for, and look up ~ the alternate if so. dup 0 swap ~ (name as stack string, name pointer, placeholder, name pointer) dup s" create" stringcmp 0 = { swap drop ' Lcreate swap } if dup s" :" stringcmp 0 = { swap drop ' L: swap } if dup s" ;" stringcmp 0 = { swap drop ' L; swap } if dup s" ;asm" stringcmp 0 = { swap drop ' L;asm swap } if drop swap ~ (name as stack string, 0 or alternate entry pointer, name pointer) ~ If an alternate was found, the alternate will be used in immediate mode. ~ If not, we look up the word in the regular, non-transformed dictionary ~ and use that for immediate mode. over { dup transform-state transform-state-saved-latest @ swap find-in 3roll drop swap } unless ~ (name as stack string, immediate entry pointer, name pointer) ~ In regular "interpret", we would check whether we found the word before ~ checking the mode. However, we have three different places words could ~ come from, so that's not a simple notion. So, we check the mode first. interpreter-flags @ 0x01 & { ~ If we're in compile mode, there's still a chance it's an immediate ~ word. First check whether we have an immediate entry, then if so, check ~ that entry's flags. Notice that this means the generated code can't ~ override an immediate word with a non-immediate word of the same name. over dup { entry-flags@ 0x01 & not } if { ~ Either there was no immediate entry, or the immediate entry wasn't ~ flagged as an immediate word. So we check whether this could be a ~ compilation. ~ ~ To do this, we need to look the word up in the output buffer. We ~ can't easily traverse the next-entry pointers in the output buffer's ~ dictionary, so we check the label. Since we don't know the word's name ~ statically, this is a rare scenario where we can't use the abbreviated ~ label syntax, but that's easy enough. ~ ~ Even though we've ruled out the possibility that the word is only ~ ever used immediately, it is still possible that there's some reason ~ the word doesn't exist. In particular, it could be an integer literal. ~ If we were to call use-label first, that would count as a requirement ~ that the label must eventually be set. We don't want to require that ~ quite yet, so we call find-label. ~ ~ This check is the means by which forward references are disallowed: ~ On the very first pass, a forward-referenced label won't exist yet, so ~ transform will give a "no such word" error, which in an ideal world ~ would prevent there from being a subsequent pass, but at the very ~ least it will ensure the output isn't a valid ELF. dup swap-transform-variables find-label swap-transform-variables { ~ It exists, so we declare our use of it (that's also the only way to ~ get a value for it). swap-transform-variables intern-label use-label swap-transform-variables ~ Labels point to codewords (because that's what "Lcreate" does), ~ which is already what we want to output. ~ ~ An important caveat: Though it would require something weird to be ~ happening, such as a forced forward reference, the label may be zero! ~ We need to allow for that possibility by not examining the contents of ~ a nonexistent entry. ~ ~ Fortunately we don't have to look at it, just append it to the heap ~ and clean up. drop , dropstring 0 exit } if } if } if ~ (name as stack string, immediate entry pointer, name pointer) ~ If we got here, one of three things is true: We're in interpret mode; ~ the word is immediate; or no word was found. If the immediate entry ~ pointer is non-zero, run it. over { drop dropstring-with-result entry-to-execution-token execute 0 exit } if ~ If we're still here, it wasn't in the dictionary. Also, we don't need ~ the immediate entry pointer, either. drop drop ~ (name as stack string) ~ If it's not in the dictionary, check whether it's an integer literal. As ~ before, we get the stack address and use it as a string pointer. value@ read-integer 0 = { ~ It's a number. interpreter-flags @ 0x01 & { ~ We're in compile mode; append first "lit", then the number, to the ~ heap. The version of "lit" we use is the one that's current when we ~ ourselves are compiled, hardcoded; doing a dynamic lookup would ~ require dealing with what happens if it's not found. ~ TODO this is wrong dropstring-with-result ~ We look up "lit" as a label. swap-transform-variables L@' lit swap-transform-variables transform-offset , , 0 exit } if ~ We're in interpret mode; push the number to the stack. Or at least, that's ~ what the code we're interpreting will see. Really it's already on the ~ stack, just clean everything else up and leave it there. dropstring-with-result 0 exit } if ~ If it's neither in the dictionary nor a number, just print an error. s" No such word: " emitstring value@ emitstring dropstring 0 ; ~ This implements the label transform for all words in a region given as an ~ input string. It is directly analogous to "quit", in interpret.e, but is far ~ more complex. ~ ~ (output buffer start, output point, input string pointer ~ -- output buffer start, output point) : transform main-input-buffer dup push-input-buffer ~ TODO the arguments for this seem to be backwards from the documentation swap attach-string-to-input-buffer ~ Save the old values of "here" and "latest", and set the initial values ~ of the internal ones. These values need to persist across iterations, ~ since client code will make its own updates to them and then rely on those ~ updates having taken effect. So we do the swap just once, here outside the ~ loop, and set it back when the loop ends. here @ transform-state transform-state-saved-here ! latest @ transform-state transform-state-saved-latest ! over transform-state transform-state-output-buffer-start ! here ! 0 latest ! ~ Now the stack has nothing of ours on it, so client code can do its thing. ~ It's important that the stack has nothing of ours on it that persists ~ across iterations, so that client code can add and remove stuff there as ~ it sees fit. { transform-one ~ (done) ~ When the loop is done, get the real values of "here" and "latest" ~ back. The internal "here" is also the output point, and will become our ~ return value. The internal "latest" is discarded. { here @ transform-state transform-state-saved-here @ here ! transform-state transform-state-saved-latest @ latest ! ~ (output point) ~ Though we don't actually use transform-state outside of this ~ invocation, for tidiness we zero it out. 0 transform-state transform-state-saved-here ! 0 transform-state transform-state-saved-latest ! 0 transform-state transform-state-output-buffer-start ! ~ Also put the input source back how it was. main-input-buffer pop-input-buffer exit } if } forever ;