forked from mirrors/nixpkgs
doc: Render lib.fixedPoints
This commit is contained in:
Robert Hensing
parent
e08fab0406
commit
aa1beb0ab5
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@ -11,6 +11,7 @@ let
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{ name = "strings"; description = "string manipulation functions"; }
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{ name = "versions"; description = "version string functions"; }
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{ name = "trivial"; description = "miscellaneous functions"; }
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{ name = "fixedPoints"; baseName = "fixed-points"; description = "explicit recursion functions"; }
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{ name = "lists"; description = "list manipulation functions"; }
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{ name = "debug"; description = "debugging functions"; }
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{ name = "options"; description = "NixOS / nixpkgs option handling"; }
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@ -14,13 +14,16 @@ stdenv.mkDerivation {
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buildInputs = [ nixdoc ];
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installPhase = ''
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function docgen {
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# TODO: wrap lib.$1 in <literal>, make nixdoc not escape it
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if [[ -e "../lib/$1.nix" ]]; then
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nixdoc -c "$1" -d "lib.$1: $2" -l ${locationsJSON} -f "$1.nix" > "$out/$1.md"
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name=$1
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baseName=$2
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description=$3
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# TODO: wrap lib.$name in <literal>, make nixdoc not escape it
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if [[ -e "../lib/$baseName.nix" ]]; then
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nixdoc -c "$name" -d "lib.$name: $description" -l ${locationsJSON} -f "$baseName.nix" > "$out/$name.md"
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else
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nixdoc -c "$1" -d "lib.$1: $2" -l ${locationsJSON} -f "$1/default.nix" > "$out/$1.md"
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nixdoc -c "$name" -d "lib.$name: $description" -l ${locationsJSON} -f "$baseName/default.nix" > "$out/$name.md"
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fi
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echo "$out/$1.md" >> "$out/index.md"
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echo "$out/$name.md" >> "$out/index.md"
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}
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mkdir -p "$out"
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@ -29,8 +32,8 @@ stdenv.mkDerivation {
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```{=include=} sections
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EOF
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${lib.concatMapStrings ({ name, description }: ''
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docgen ${name} ${lib.escapeShellArg description}
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${lib.concatMapStrings ({ name, baseName ? name, description }: ''
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docgen ${name} ${baseName} ${lib.escapeShellArg description}
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'') libsets}
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echo '```' >> "$out/index.md"
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@ -1,34 +1,49 @@
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{ lib, ... }:
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rec {
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# Compute the fixed point of the given function `f`, which is usually an
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# attribute set that expects its final, non-recursive representation as an
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# argument:
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#
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# f = self: { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; }
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#
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# Nix evaluates this recursion until all references to `self` have been
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# resolved. At that point, the final result is returned and `f x = x` holds:
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#
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# nix-repl> fix f
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# { bar = "bar"; foo = "foo"; foobar = "foobar"; }
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#
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# Type: fix :: (a -> a) -> a
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#
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# See https://en.wikipedia.org/wiki/Fixed-point_combinator for further
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# details.
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/*
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Compute the fixed point of the given function `f`, which is usually an
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attribute set that expects its final, non-recursive representation as an
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argument:
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```
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f = self: { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; }
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```
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Nix evaluates this recursion until all references to `self` have been
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resolved. At that point, the final result is returned and `f x = x` holds:
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```
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nix-repl> fix f
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{ bar = "bar"; foo = "foo"; foobar = "foobar"; }
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```
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Type: fix :: (a -> a) -> a
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See https://en.wikipedia.org/wiki/Fixed-point_combinator for further
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details.
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*/
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fix = f: let x = f x; in x;
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# A variant of `fix` that records the original recursive attribute set in the
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# result. This is useful in combination with the `extends` function to
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# implement deep overriding. See pkgs/development/haskell-modules/default.nix
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# for a concrete example.
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/*
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A variant of `fix` that records the original recursive attribute set in the
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result, in an attribute named `__unfix__`.
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This is useful in combination with the `extends` function to
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implement deep overriding.
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*/
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fix' = f: let x = f x // { __unfix__ = f; }; in x;
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# Return the fixpoint that `f` converges to when called recursively, starting
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# with the input `x`.
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#
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# nix-repl> converge (x: x / 2) 16
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# 0
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/*
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Return the fixpoint that `f` converges to when called iteratively, starting
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with the input `x`.
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```
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nix-repl> converge (x: x / 2) 16
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0
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```
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Type: (a -> a) -> a -> a
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*/
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converge = f: x:
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let
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x' = f x;
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@ -37,75 +52,94 @@ rec {
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then x
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else converge f x';
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# Modify the contents of an explicitly recursive attribute set in a way that
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# honors `self`-references. This is accomplished with a function
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#
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# g = self: super: { foo = super.foo + " + "; }
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#
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# that has access to the unmodified input (`super`) as well as the final
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# non-recursive representation of the attribute set (`self`). `extends`
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# differs from the native `//` operator insofar as that it's applied *before*
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# references to `self` are resolved:
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#
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# nix-repl> fix (extends g f)
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# { bar = "bar"; foo = "foo + "; foobar = "foo + bar"; }
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#
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# The name of the function is inspired by object-oriented inheritance, i.e.
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# think of it as an infix operator `g extends f` that mimics the syntax from
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# Java. It may seem counter-intuitive to have the "base class" as the second
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# argument, but it's nice this way if several uses of `extends` are cascaded.
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#
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# To get a better understanding how `extends` turns a function with a fix
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# point (the package set we start with) into a new function with a different fix
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# point (the desired packages set) lets just see, how `extends g f`
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# unfolds with `g` and `f` defined above:
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#
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# extends g f = self: let super = f self; in super // g self super;
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# = self: let super = { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; }; in super // g self super
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# = self: { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; } // g self { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; }
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# = self: { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; } // { foo = "foo" + " + "; }
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# = self: { foo = "foo + "; bar = "bar"; foobar = self.foo + self.bar; }
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#
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/*
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Modify the contents of an explicitly recursive attribute set in a way that
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honors `self`-references. This is accomplished with a function
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```nix
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g = self: super: { foo = super.foo + " + "; }
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```
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that has access to the unmodified input (`super`) as well as the final
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non-recursive representation of the attribute set (`self`). `extends`
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differs from the native `//` operator insofar as that it's applied *before*
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references to `self` are resolved:
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```
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nix-repl> fix (extends g f)
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{ bar = "bar"; foo = "foo + "; foobar = "foo + bar"; }
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```
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The name of the function is inspired by object-oriented inheritance, i.e.
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think of it as an infix operator `g extends f` that mimics the syntax from
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Java. It may seem counter-intuitive to have the "base class" as the second
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argument, but it's nice this way if several uses of `extends` are cascaded.
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To get a better understanding how `extends` turns a function with a fix
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point (the package set we start with) into a new function with a different fix
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point (the desired packages set) lets just see, how `extends g f`
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unfolds with `g` and `f` defined above:
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```
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extends g f = self: let super = f self; in super // g self super;
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= self: let super = { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; }; in super // g self super
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= self: { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; } // g self { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; }
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= self: { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; } // { foo = "foo" + " + "; }
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= self: { foo = "foo + "; bar = "bar"; foobar = self.foo + self.bar; }
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```
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*/
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extends = f: rattrs: self: let super = rattrs self; in super // f self super;
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# Compose two extending functions of the type expected by 'extends'
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# into one where changes made in the first are available in the
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# 'super' of the second
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/*
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Compose two extending functions of the type expected by 'extends'
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into one where changes made in the first are available in the
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'super' of the second
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*/
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composeExtensions =
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f: g: final: prev:
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let fApplied = f final prev;
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prev' = prev // fApplied;
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in fApplied // g final prev';
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# Compose several extending functions of the type expected by 'extends' into
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# one where changes made in preceding functions are made available to
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# subsequent ones.
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#
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# composeManyExtensions : [packageSet -> packageSet -> packageSet] -> packageSet -> packageSet -> packageSet
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# ^final ^prev ^overrides ^final ^prev ^overrides
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/*
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Compose several extending functions of the type expected by 'extends' into
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one where changes made in preceding functions are made available to
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subsequent ones.
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```
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composeManyExtensions : [packageSet -> packageSet -> packageSet] -> packageSet -> packageSet -> packageSet
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^final ^prev ^overrides ^final ^prev ^overrides
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```
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*/
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composeManyExtensions =
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lib.foldr (x: y: composeExtensions x y) (final: prev: {});
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# Create an overridable, recursive attribute set. For example:
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#
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# nix-repl> obj = makeExtensible (self: { })
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#
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# nix-repl> obj
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# { __unfix__ = «lambda»; extend = «lambda»; }
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#
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# nix-repl> obj = obj.extend (self: super: { foo = "foo"; })
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#
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# nix-repl> obj
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# { __unfix__ = «lambda»; extend = «lambda»; foo = "foo"; }
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#
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# nix-repl> obj = obj.extend (self: super: { foo = super.foo + " + "; bar = "bar"; foobar = self.foo + self.bar; })
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#
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# nix-repl> obj
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# { __unfix__ = «lambda»; bar = "bar"; extend = «lambda»; foo = "foo + "; foobar = "foo + bar"; }
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/*
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Create an overridable, recursive attribute set. For example:
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```
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nix-repl> obj = makeExtensible (self: { })
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nix-repl> obj
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{ __unfix__ = «lambda»; extend = «lambda»; }
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nix-repl> obj = obj.extend (self: super: { foo = "foo"; })
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nix-repl> obj
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{ __unfix__ = «lambda»; extend = «lambda»; foo = "foo"; }
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nix-repl> obj = obj.extend (self: super: { foo = super.foo + " + "; bar = "bar"; foobar = self.foo + self.bar; })
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nix-repl> obj
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{ __unfix__ = «lambda»; bar = "bar"; extend = «lambda»; foo = "foo + "; foobar = "foo + bar"; }
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```
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*/
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makeExtensible = makeExtensibleWithCustomName "extend";
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# Same as `makeExtensible` but the name of the extending attribute is
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# customized.
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/*
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Same as `makeExtensible` but the name of the extending attribute is
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customized.
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*/
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makeExtensibleWithCustomName = extenderName: rattrs:
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fix' (self: (rattrs self) // {
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${extenderName} = f: makeExtensibleWithCustomName extenderName (extends f rattrs);
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