74 lines
2.8 KiB
Markdown
74 lines
2.8 KiB
Markdown
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## Introduction
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As there are no tutorials (that I know of) on how to add new features to the nimrod
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compiler I have decided to make one, based on me implementing the `requires`
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pragma which will be used for Babel Packages.
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As with many tasks there are many tools that are very helpful, I have used
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the *nimgrep* tool which is in the tools/ directory in Nimrod's repository, but I'm sure you know of other tools which can be very helpful!
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## First steps
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The first thing I have decided to do was create a test file, it follows:
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{.requires packageA "0.7" "0.9".}
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echo("hi")
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(It originally had a `..` between the two string literals, I decided to get rid
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of that because I noticed that pragmas don't support it, I might come back to it.)
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I then saved that file as *"pragmaTest.nim"* and compiled it with
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`nimrod c pragmaTest.nim`. This has caused `pragmaTest.nim(1, 10) Error: invalid pragma: requires`.
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The next step was quite obvious, searching for "invalid pragma:", `nimgrep --recursive --ext:nim "invalid\ pragma:"`,
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this only gives one result.
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../Nimrod/rod/msgs.nim
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258: errInvalidPragmaX: "invalid pragma: $1",
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After some more intellectual grepping and looking through files, I noticed that the pragma() function in pragmas.nim
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takes an argument called `validPragmas` this lead me to *semtypes.nim* and *semstmts.nim*
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after searching for (yes, you've guessed it) `pragma(`(please note this needs escaping when used as a regex).
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There was many `pragma` calls, I have looked at most of them and since I wanted
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a "global"(not sure if that's the correct term) pragma, for example
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`{.warning: "warning".}`. The `pragma` function is called with many different
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valid pragma groups. There is among many others, `stmtPragmas`, which is what
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I wanted, it's defined in *pragmas.nim*.
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## Hacking the code!
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I found where `TSpecialWords` is defined(*wordrecg.nim*) and added `wRequires`
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there, to the `specialWords` array below, and also to `stmtPragmas`. I then added `wRequires` to the case statement in the `pragma` function in *pragmas.nim*.
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This is where the `debug` function came into play, it is a function that pretty prints a
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node in the AST, it is very useful. I added two `debug` calls one for the 'it' node
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and another one for the 'n' node.
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I then bootstrapped by executing `./koch boot`. After I got the beautiful "SUCCESS",
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I compiled *pragmaTest.nim*. And I got this output:
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{
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"kind": "nkIdent",
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"ident": "requires"
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}
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{
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"kind": "nkPragma",
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"sons": [
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{
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"kind": "nkIdent",
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"ident": "requires"
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},
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{
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"kind": "nkIdent",
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"ident": "packageA"
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},
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{
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"kind": "nkStrLit",
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"strVal": "0.7"
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},
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{
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"kind": "nkStrLit",
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"strVal": "0.9"
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}
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]
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}
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