31 lines
1 KiB
Text
31 lines
1 KiB
Text
= zexps
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zexps, similar to g-expressions in Guix, are a way to generate
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S-expressions that are tagged with store paths. The syntax in Zilch is inspired
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by it, but has been developed separately.
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A zexp is used similarly to a ``quasiquote``d value in Scheme, but has an extra type
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of unquoting, called `zexp-unquote`, which unquotes a value such as a `++<store-path>++`
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or another `zexp`.
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Each `zexp` keeps track of the derivation outputs and store files it depends on,
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similarly to how string context works in Nix:
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[,scheme]
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----
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#~(foo bar #$baz)
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; is identical to:
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(zexp (foo bar (zexp-unquote baz)))
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----
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When a `zexp-unquote` (or its reader syntax, `#$`) is encountered, the value
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contained in the `zexp` (or compatible object) is used as-is, with no
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evaluation. It is possible to mix and match `zexp-unquote` with `unquote`,
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allowing building e.g. dynamic strings from zexps. `zexp-unquote` is always
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evaluated before `unquote` is.
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[,scheme]
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----
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(define world ...)
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(define hello #~("hello" ,(string-append "very " "cute" #$world)))
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----
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