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52 lines
3 KiB
OpenEdge ABL
52 lines
3 KiB
OpenEdge ABL
What This Module Does.
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An overview of the final module's role and abilities.
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@h Prerequisites.
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The final module is a part of the Inform compiler toolset. It is
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presented as a literate program or "web". Before diving in:
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(a) It helps to have some experience of reading webs: see //inweb// for more.
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(b) The module is written in C, in fact ANSI C99, but this is disguised by the
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fact that it uses some extension syntaxes provided by the //inweb// literate
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programming tool, making it a dialect of C called InC. See //inweb// for
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full details, but essentially: it's C without predeclarations or header files,
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and where functions have names like |Tags::add_by_name| rather than just |add_by_name|.
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(c) This module uses other modules drawn from the //compiler//, and also
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uses a module of utility functions called //foundation//.
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For more, see //foundation: A Brief Guide to Foundation//.
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@h Finally final.
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The final module is aptly named, in that it is the very last stage in compiling
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an Inform project. Everything up to this module has been generating a tree of
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Inter code, which is (to a large extent) an abstract, general-purpose description
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of a program. We finally turn that into an Inform 6 program, or a C program,
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or some other concrete expression of that program.
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This module has a very simple interface to the rest of the tool chain: it
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simply provides a single Inter pipeline stage called |generate|. See
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//CodeGen::create_pipeline_stage//. When this stage is reached, the function
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//CodeGen::run_pipeline_stage// is run. This then creates a //code_generation//
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object, which holds all the temporary storage and configuration details for a
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single act of code-generation. The most important of those details is the
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choice of which //code_generator// to use -- see below.
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@ The module creates a small number of //code_generator//s, one for each
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possible output format. For example, //I6Target::create_generator// creates
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one which represents "output Inform 6 code, please"; //CTarget::create_generator//
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creates one for "output ANSI C-99 code, please".
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If you are considering adding a new output format, say for JavaScript or Python,
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that should be done by adding a new //code_generator//. Although the default
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generator is the Inform 6 one, that is in some ways misleadingly simple in
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design because Inter, our intermediate format, was originally designed as a
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sort of abstract paraphrase of Inform 6 -- which means that it's quite easy
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to turn Inter to I6. The C code generator is a much better example of the real
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issues likely to present themselves. So reading through the chapter on C is
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probably the best way to get an idea of the task.
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@ It seems likely that many if not most of the formats we will ever need to
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generate will be procedural programming languages of the sort usually called
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C-like, and we want to avoid duplicated effort. A generic algorithm called
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//Vanilla// is therefore provided: a generator can, if it wishes, make use of
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this to simplify its work, and both our C and Inform 6 generators do so.
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