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134 lines
7.4 KiB
Plaintext
Executable file
134 lines
7.4 KiB
Plaintext
Executable file
Title: Structure of the Inform 7 compiler
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Author: Graham Nelson
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@ The core Inform compiler combines natural-language source text, including
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natural-language extensions, and precompiled "kits" in order to make the
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instructions for making a playable story. Inform is internally divided into
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Stages, numbered 1 to 7:[1]
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(1) Build management: gathering up what must be compiled and reading it in as
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an annotated syntax tree, or "AST".[2]
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(2) Queueing and organising work which will be done by stages 3 to 5.
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(3) Turning assertion sentences -- "Peter is a man", "The tally is a number
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that varies" -- into a world model of variables, kinds, instances and properties.
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Values and typechecking are also managed here. Phrases and rules are identified,
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but their bodies are ignored for the moment.
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(4) The world model, phrases and rules identified by stage (3) are now compiled
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to an Intermediate Representation, or "IR", another sort of tree known as Inter.
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This is done by calling down to the API provided by...
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(5) ... which is more a layer than a stage: it's a comprehensive system for
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building Inter code, and could conceivably be used by other compilers too.
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(6) A "pipeline" of transformations on the Inter code improves it. A weak form
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of linker[3] joins on precompiled Inter code from "kits" such as BasicInformKit
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or WorldModelKit.
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(7) The finished Inter tree is then code-generated to form our output, which
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can be in several different formats, and an Index mini-website about it is made.
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For most users of the Inform app, the format will be Inform 6, and further
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command-line tools //inform6// and //inblorb// then turn that into a "story
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file" and then a Javascript-running web page; but for some command-line users,
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the format is C and a compiler like |clang| is then used to make an executable.
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[1] These slightly overlap in chronological order, so maybe Level would be a
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better name than Stage, but then again they do mostly happen in sequence.
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[2] AST normally stands for "abstract syntax tree" but we prefer "annotated",
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skirting the issue of exactly how abstract vs concrete it is.
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[3] Weak in that the //inter// tool can link any number of kits to a source text,
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but not a source text to a source text.
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@ These seven stages form a single code base but are packaged up into three
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command-line tools, not one:
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(*) |inbuild| is Stage 1 as a stand-alone tool: see //this description -> inbuildn//.
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(*) |inform7| is Stages 1 to 7 as an all-in-one: see //this description -> inform7n//
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of the part unique to it, Stages 2 to 4.
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(*) |inter| is Stages 5 to 7 as a stand-alone tool: see //this description -> intern//.
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All three tools also use a large library of //services//: everything from
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inflecting words to simplifying logical propositions.
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@ The flow of data looks like so, with time running downwards on the page:
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= (hyperlinked text as BoxArt)
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kit sources
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(in Inform 6 code)
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| INTER
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\|/
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precompiled
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Inter trees
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. main source text extension source texts
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. \ /
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. \ / INFORM7 Stage 1 or INBUILD
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. \ /
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. \|/ \|/
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. syntax tree
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. |
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. | INFORM7 Stages 2 to 4/5
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. |
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. . . . . . . precompiled \|/
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Inter trees Inter tree
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\ /
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\ / INFORM7 Stage 6 or INTER
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\|/ \|/
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single linked Inter tree
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/ | \
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/ | \ INFORM7 Stage 7 or INTER
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\|/ \|/ \|/
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Inform 6 code C code index mini-website
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: :
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INFORM6 : : CLANG or GCC
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\:/ \:/
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story file executable
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:
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INBLORB :
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\:/
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playable website
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=
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@ The code base is subdivided into "modules". There are around 30, from five sources:
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(*) A set of //services//, which are libraries of code providing features useful
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to programs dealing with natural language.
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(*) Those //owned by Inbuild -> inbuildn//.
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(*) Those //owned by Inform7 -> inform7n//.
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(*) Those //owned by Inter -> intern//.
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(*) The //foundation// library for memory-management, string handling and so
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on, which is a module held in the //inweb// repository rather than here.
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@ The full breakdown of the three compiler tools into modules is as follows.
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An |o| means that the tool is the owner of the module in question; a |x| means
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that it imports the module from somewhere else.
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= (hyperlinked text as BoxArt)
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WEB ACTIVE STAGES INWEB SERVICES INBUILD INFORM7 INTER
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//inbuild// cli Before - - o - -
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//inform7// cli Before - - - o -
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//inter// cli Before - - - - o
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//supervisor// module Stage 1 - - o x -
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//core// module Stage 2 - - - o -
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//assertions// module Stage 3 - - - o -
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//values// module Stage 3 - - - o -
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//knowledge// module Stage 3 - - - o -
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//if// module Stage 3 - - - o -
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//multimedia// module Stage 3 - - - o -
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//imperative// module Stage 4 - - - o -
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//runtime// module Stage 4 - - - o -
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//bytecode// module Stage 5 - - - x o
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//building// module Stage 5 - - - x o
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//pipeline// module Stage 6 - - - x o
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//final// module Stage 7 - - - x o
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//index// module Stage 7 - - - x o
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//linguistics// service Throughout - o - x -
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//calculus// service Throughout - o - x -
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//kinds// service Throughout - o - x -
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//lexicon// service Throughout - o - x -
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//inflections// service Throughout - o - x -
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//problems// service Throughout - o - x -
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//syntax// service Throughout - o x x -
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//words// service Throughout - o x x x
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//arch// service Throughout - o x x x
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//html// service Throughout - o x x x
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//foundation// library Throughout o - x x x
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=
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The executables otherwise contain only a few POSIX or Windows-related functions
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for file and directory handling, and functions from the standard C library.
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There are, therefore, no external dependencies.
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