[erlang-questions] Deep data structures and lenses

Ulf Wiger <>
Mon Sep 21 14:22:12 CEST 2015


> On 12 Sep 2015, at 19:51, Guilherme Andrade <> wrote:
> 
> Partially inspired by jlouis' erl-lenses[1] and an old discussion on this mailing list[2], I've been sketching a library for easier manipulation (both data fetching and updating) of deep data structures

Another library that’s been inspired by erl-lenses (although this has perhaps not been well communicated) is exprecs in parse_trans.

Example:

-module(lens).

-include_lib("parse_trans/include/exprecs.hrl").

-export([t/0]).

-record(r, {a, b, c}).
-export_records([r]).

t() ->
    R = '#new-r'([{a,1},{b,2},{c,3}]),
    {GetA, SetA} = Lens = '#lens-r'(a),
    GetA1 = GetA(R),
    R1 = SetA(17, R),
    GetA2 = GetA(R1),
    [{lens, Lens},
     {get_a, GetA1},
     {set_a, 17, R1},
     {get_a, GetA2}].

...

Eshell V5.10.4  (abort with ^G)
1> c(lens).
{ok,lens}
2> lens:t().
[{lens,{#Fun<lens.6.121208397>,#Fun<lens.7.121208397>}},
 {get_a,1},
 {set_a,17,{r,17,2,3}},
 {get_a,17}]

BR,
Ulf W

Ulf Wiger, Co-founder & Developer Advocate, Feuerlabs Inc.
http://feuerlabs.com



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