Add binary to the crate (#20)

[micouy]

This PR adds a binary of the same name to the crate. It introduces a breaking change in the API. Resolves #21, resolves #20.

Changes

• Add src/main.rs.

• Change Shape::Continous in src/lib.rs.

  Before:

  pub enum Shape<'a> {
   Continuous(fn(f32) -> f32),
   ...
  }

  After:

  pub enum Shape<'a> {
   Continuous(Box<dyn FnMut(f32) -> f32 + 'a>),
   ...
  }

  This is a breaking change in the API, so the minor version must be increased. I explained the motivation behind it in #21. I don't believe it is possible to add a dynamic math expression parser without introducing this change.

  I also added #![feature(box_syntax)] on top of every example and box before each closure, including the examples in documentation and README.md. If you do not wish to include this line each time you can switch to stable syntax: Box::new(...). Alternative solutions are provided in #21.

  This change is incompatible with #14 (no_std support) as it requires allocating Boxes. A possible solution is to use references or generic types in Shape. Another solution is to move drawing logic from Chart to shapes and introduce a Shape trait instead of an enum with predefined types in its fields.

• Change version in Cargo.toml to 0.6.0.

• Set edition = "2018" in Cargo.toml. Add bin and lib sections to Cargo.toml.

  This makes configuring a separate binary and library easier. I also removed each extern crate since they are not necessary in the 2018 edition.

• Use clap to parse args and display pretty info about the binary.
• Use meval to parse math expressions.

Behavior

Basic usage (prints the formula and displays the plot)

$ textplots 'e ^ (1 / x)'

Error info on no formula

$ textplots
error: The following required arguments were not provided:
    <FORMULA>

USAGE:
    textplots <FORMULA>

For more information try --help

--help

$ textplots --help
textplots 0.6.0
Alexey Suslov <alexey.suslov@gmail.com>
Terminal plotting library.

USAGE:
    textplots <FORMULA>

FLAGS:
    -h, --help       Prints help information
    -V, --version    Prints version information

ARGS:
    <FORMULA>    Formula to plot

Error info on unknown variable

$ textplots 'y'
Evaluation error: unknown variable `y`.

Error on unexpected token

$ textplots `100x`
Parse error: Unexpected token at byte 3.

Possible future development

• Custom math parsing errors.
• Multiple plots.
• Colors (#10).
• Receiving input from pipes.

[loony-bean]

Hi @micouy! I really like what you did, and the write-up is excellent. Thank you ❤️ I'd like to get this merged and see how people might use it.

Do you think you can make it compatible with stable Rust before we go on?

[micouy]

You mean the box syntax? Sure thing, I can change it to Box::new. What about the no_std thing? I could change Continous(Box<dyn Fn + 'a>) to Continous(&'a dyn Fn) so as not to introduce more allocations, the enum already has the lifetime parameter. Since you're already breaking the API, you could also change it to use traits and move drawing logic to the shapes. Then you could merge my changes with the no_std update but that would probably take ages without more contributors.

[loony-bean]

I'm fine with dropping no_std support idea. I'm not yet sure there is a lot of utility in a library like that on embedded device.

[micouy]

Done. I've added one example with box syntax in README.md and in src/lib.rs. Just remove them if you do not wish them to be there. Remember to say something about the binary in README.md. I also suggest adding a small demo.