https://github.com/williamthome/custom_sigils
https://github.com/williamthome/custom_sigils
Last synced: 21 days ago
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- Host: GitHub
- URL: https://github.com/williamthome/custom_sigils
- Owner: williamthome
- Created: 2025-03-26T10:57:01.000Z (about 1 month ago)
- Default Branch: main
- Last Pushed: 2025-03-26T11:54:09.000Z (about 1 month ago)
- Last Synced: 2025-03-26T12:29:59.833Z (about 1 month ago)
- Language: Erlang
- Size: 2.93 KB
- Stars: 0
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# custom_sigils
This is a POC of custom sigils implementation for Erlang/OTP.
It is based on [this comment](https://erlangforums.com/t/proposal-introduce-f-sigils-for-string-interpolation/4551/21?u=williamthome)
on the Erlang Forums.
This is a minimal change and does not break any existing code.
## How it works
The developer can use the built-in sigils, like `s`, `S`, `b`, and `B`, but it
can also use any sigil it wants. However, it is obligated to handle the custom
sigil with parse transform, otherwise, an `invalid sigil` exception will be raised
at the compile time.
### Why parse transform?
It was the first idea and seems to be the simplest one to implement this feature.
## Examples
There are two functions of custom sigils implemented in this project:
- `json`: Decodes a JSON into an Erlang term via `json:decode/1`
- `sql`: Transforms a SQL query into a tuple based on the `f_sigil` proposal.
This sigil extracts the params and replaces them with `$N`, where N is the
param index of that param.
### The code of the `example` module
```erlang
-module(example).
-compile({parse_transform, json_sigil}).
-compile({parse_transform, sql_sigil}).
%% Sigils can be defined globally in rebar3.config (applies to all .erl files), e.g.:
%{erl_opts, [
% {parse_transform, json_sigil},
% {parse_transform, sql_sigil}
%]}.
-export([json/0]).
-export([sql/2]).
json() ->
~json"""
{"key": "value"}
""".
sql(Name, MinAge) when is_binary(Name); is_integer(MinAge) ->
~sql"""
SELECT *
FROM users
WHERE name = {Name}
AND age >= {MinAge}
""".
%% Uncomment this function to raise an invalid sigil exception.
%invalid() ->
% ~invalid"".
```
### The `json_sigil` code
```erlang
-module(json_sigil).
-export([parse_transform/2]).
parse_transform(Forms0, _Options) ->
Forms = [erl_syntax_lib:map(fun(Node) ->
transform_node(erl_syntax:revert(Node))
end, F) || F <- Forms0],
erl_syntax:revert_forms(Forms).
transform_node({sigil, _Anno, json, String, _Suffix}) ->
Bin = erl_syntax:binary([erl_syntax:binary_field(
String,
[erl_syntax:atom(utf8)])]),
erl_syntax:application(erl_syntax:atom(json),
erl_syntax:atom(decode),
[Bin]);
transform_node(Node) ->
Node.
```
### The `sql_sigil` code
Please refer to the project module for the complete code.
### Running the examples
```erlang
1> c(json_sigil), c(sql_sigil), c(example).
{ok,example}
2> example:json().
#{<<"key">> => <<"value">>}
3> example:sql(~"Bob", 18).
{sql,<<"SELECT *\n FROM users\n WHERE name = $1\n AND age >= $2">>,
[<<"Bob">>,18]}
4> ~invalid"".
* 1:1: invalid sigil
```