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authorEelco Dolstra <e.dolstra@tudelft.nl>2004-10-25T16·54+0000
committerEelco Dolstra <e.dolstra@tudelft.nl>2004-10-25T16·54+0000
commit37d7abd69402f0e7a78d4d2f2d78996409a8563a (patch)
treebf844e4486b0e055921583c4b7c2d3d843b34485 /src/nix-instantiate
parentf4d44a002688262d33093494a7fea1bb11b97ac9 (diff)
* New language feature: with expressions.
  The expression `with E1; E2' evaluates to E2 with all bindings in
  the attribute set E1 substituted.  E.g.,

    with {x = 123;}; x

  evaluates to 123.  That is, the attribute set E1 is in scope in E2.

  This is particularly useful when importing files containing lots
  definitions.  E.g., instead of

    let {
      inherit (import ./foo.nix) a b c d e f;

      body = ... a ... f ...;
    }

  we can now say

    with import ./foo.nix;

    ... a ... f ...

  I.e., we don't have to say what variables should be brought into scope.

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