# Collection of Erlang Parse Transforms
[](https://github.com/saleyn/etran/actions/workflows/erlang.yml)
[](https://hex.pm/packages/etran)
[](https://hex.pm/packages/etran)
This library includes useful parse transforms including Elixir-like pipeline operator for
cascading function calls.
## Author
Serge Aleynikov <saleyn(at)gmail.com>
## Content
| Module | Description |
| --------------------- | ------------------------------------------------------------------------------------ |
| erlpipe | Elixir-like pipeline for Erlang |
| iif | Ternary if function including `iif/3`, `iif/4`, `ife/3`, `ife/4` parse transforms |
| str | Stringification functions including `str/1`, `str/2`, and `throw/2` parse transforms |
### Erlang Pipeline (`erlpipe`)
Inspired by the Elixir's `|>` pipeline operator.
This tranform makes code with cascading function calls much more readable by using the `/` as the
pipeline operator. The result of evaluation of the LHS expression is passed as an argument to
the RHS expression.
It transforms code from:
```erlang
print(L) when is_list(L) ->
[lists:split(3, L)] / element(1, _) %% Function calls must be enclosed in `[...]`
/ io:format("~s\n", [_]).
test1(Arg1, Arg2, Arg3) ->
[Arg1, Arg2] %% Variables must be enclosed in `[...]`
/ fun1
/ mod:fun2
/ fun3() %% In function calls parenthesis are optional
/ fun4(Arg3, _)
/ io_lib:format("~p\n", [_])
/ fun6([1,2,3], _, other_param)
/ fun7.
test2() ->
3 = "abc" / length, %% Strings can be passed to '/' as is
"abc" = <<"abc">> / binary_to_list, %% Binaries can be passed to '/' as is
"1,2,3" = {$1,$2,$3} / tuple_to_list %% Tuples can be passed to '/' as is
/ [[I] || I <- _]
/ string:join(_, ","),
"abc\n" = "abc" / (_ ++ "\n"), %% Can use operators on the right hand side
2.0 = 4.0 / max(1.0, 2.0), %% Expressions with lhs floats are unmodified
2 = 4 / max(1, 2). %% Expressions with lhs integers are unmodified
```
to the following equivalent:
```erlang
print(L) when is_list(L) ->
io:format("~s\n", [element(1, lists:split(3, L))]).
test1(Arg1, Arg2, Arg3) ->
fun7(fun6([1,2,3],
io_lib:format("~p\n", [fun4(Arg3, fun3(mod2:fun2(fun1(Arg1, Arg2))))]),
other_param)).
test2() ->
3 = length("abc"),
"abc" = binary_to_list(<<"abc">>),
"1,2,3" = string:join([[I] || I <- tuple_to_list({$1,$2,$3})], ","),
"abc\n" = "abc" ++ "\n",
2.0 = 4.0 / max(1.0, 2.0),
2 = 4 / max(1, 2).
```
Similar attempts to tackle this pipeline transform have been done by other developers:
* https://github.com/stolen/pipeline
* https://github.com/oltarasenko/epipe
* https://github.com/clanchun/epipe
* https://github.com/pouriya/pipeline
Yet, we subjectively believe that the choice of syntax in this implementation of transform
is more succinct and elegant, and doesn't attempt to modify the meaning of the `/` operator
for arithmetic LHS types (i.e. integers and floats).
### Ternary if (`iif`)
This transform improves the code readability for cases that involve simple conditional tests.
E.g.:
```erlang
iif(tuple_size(T) == 3, good, bad).
iif(some_fun(A), match, ok, error).
nvl(L, undefined).
nvl(L, nil, hd(L))
```
are transformed to:
```erlang
case tuple_size(T) == 3 of
true -> good;
_ -> bad
end.
case some_fun(A) of
match -> ok;
nomatch -> error
end.
case L of
[] -> undefined;
false -> undefined;
undefined -> undefined;
_ -> L
end.
case L of
[] -> nil;
false -> nil;
undefined -> nil;
_ -> hd(L)
end.
```
### String transforms (`str`)
This module implements a transform to stringify an Erlang term.
* `str(Term)` is equivalent to `lists:flatten(io_lib:format("~p", [Term]))`.
* `str(Fmt, Args)` is equivalent to `lists:flatten(io_lib:format(Fmt, Args))`.
* `throw(Fmt,Args)` is equivalent to `throw(lists:flatten(io_lib:format(Fmt, Args)))`.
## Dowloading
* [Github](https://github.com/saleyn/etran)
* [Hex.pm](https://hex.pm/packages/etran)
## Building and Using
```
$ make
```
To use the transforms, compile your module with the `+'{parse_transform, Module}'` command-line
option, or include `-compile({parse_transform, Module}).` in your source code, where `Module`
is one of the transform modules implemented in this project.
