forked from lix-project/lix
6d6c68c0d2
single quotes. Example (from NixOS):
job = ''
start on network-interfaces
start script
rm -f /var/run/opengl-driver
${if videoDriver == "nvidia"
then "ln -sf ${nvidiaDrivers} /var/run/opengl-driver"
else if cfg.driSupport
then "ln -sf ${mesa} /var/run/opengl-driver"
else ""
}
rm -f /var/log/slim.log
end script
'';
This style has two big advantages:
- \, ' and " aren't special, only '' and ${. So you get a lot less
escaping in shell scripts / configuration files in Nixpkgs/NixOS.
The delimiter '' is rare in scripts (and can usually be written as
""). ${ is also fairly rare.
Other delimiters such as <<...>>, {{...}} and <|...|> were also
considered but this one appears to have the fewest drawbacks
(thanks Martin).
- Indentation is intelligently stripped so that multi-line strings
can follow the nesting structure of the containing Nix
expression. E.g. in the example above 6 spaces are stripped from
the start of each line. This prevents unnecessary indentation in
generated files (which sometimes even breaks things).
See tests/lang/eval-okay-ind-string.nix for some examples.
96 lines
2.9 KiB
Modula-2
96 lines
2.9 KiB
Modula-2
init initNixExprHelpers
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Pos | string int int | Pos |
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NoPos | | Pos |
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Function | ATermList Expr Pos | Expr |
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Function1 | string Expr Pos | Expr |
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Assert | Expr Expr Pos | Expr |
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With | Expr Expr Pos | Expr |
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If | Expr Expr Expr | Expr |
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OpNot | Expr | Expr |
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OpEq | Expr Expr | Expr |
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OpNEq | Expr Expr | Expr |
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OpAnd | Expr Expr | Expr |
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OpOr | Expr Expr | Expr |
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OpImpl | Expr Expr | Expr |
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OpUpdate | Expr Expr | Expr |
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SubPath | Expr Expr | Expr |
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OpHasAttr | Expr string | Expr |
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OpPlus | Expr Expr | Expr |
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OpConcat | Expr Expr | Expr |
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ConcatStrings | ATermList | Expr |
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Call | Expr Expr | Expr |
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Select | Expr string | Expr |
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Var | string | Expr |
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Int | int | Expr |
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# Strings in the evaluator carry a so-called `context' (the ATermList)
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# which is a list of strings representing store paths. This is to
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# allow users to write things like
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#
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# "--with-freetype2-library=" + freetype + "/lib"
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#
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# where `freetype' is a derivation (or a source to be copied to the
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# store). If we just concatenated the strings without keeping track
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# of the referenced store paths, then if the string is used as a
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# derivation attribute, the derivation will not have the correct
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# dependencies in its inputDrvs and inputSrcs.
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#
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# The semantics of the context is as follows: when a string with
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# context C is used as a derivation attribute, then the derivations in
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# C will be added to the inputDrvs of the derivation, and the other
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# store paths in C will be added to the inputSrcs of the derivations.
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#
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# For canonicity, the store paths should be in sorted order.
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Str | string ATermList | Expr |
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Str | string | Expr | ObsoleteStr
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# Internal to the parser, doesn't occur in ASTs.
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IndStr | string | Expr |
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# A path is a reference to a file system object that is to be copied
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# to the Nix store when used as a derivation attribute. When it is
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# concatenated to a string (i.e., `str + path'), it is also copied and
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# the resulting store path is concatenated to the string (with the
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# store path in the context). If a string or path is concatenated to
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# a path (i.e., `path + str' or `path + path'), the result is a new
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# path (if the right-hand side is a string, the context must be
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# empty).
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Path | string | Expr |
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List | ATermList | Expr |
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BlackHole | | Expr |
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Undefined | | Expr |
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Removed | | Expr |
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PrimOp | int ATermBlob ATermList | Expr |
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Attrs | ATermList | Expr |
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Closed | Expr | Expr |
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Rec | ATermList ATermList | Expr |
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Bool | ATerm | Expr |
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Null | | Expr |
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Bind | string Expr Pos | ATerm |
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Bind | string Expr | ATerm | ObsoleteBind
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Inherit | Expr ATermList Pos | ATerm |
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Scope | | Expr |
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Formal | string ValidValues DefaultValue | ATerm |
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ValidValues | ATermList | ValidValues |
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UnrestrictedValues | | ValidValues |
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DefaultValue | Expr | DefaultValue |
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NoDefaultValue | | DefaultValue |
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True | | ATerm |
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False | | ATerm |
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PrimOpDef | int ATermBlob | ATerm |
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AttrRHS | Expr Pos | ATerm |
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eTrue = makeBool(makeTrue())
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eFalse = makeBool(makeFalse())
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