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ptGHCi

Overview

ptGHCi is an interactive command shell for Haskell designed for high-productivity interactive coding. It is implemented as a wrapper around GHCi based on Python's prompt-toolkit library and heavily inspired by IPython.

Features

Syntax highlighting

Highlighting is based on the pygments library, with a variety of styles available through the %style magic command.

Syntax highlighting

Multiline commands with automatic indentation

Use <Alt-Enter> (a.k.a. <Meta-Enter>) to start a new line. ptGHCi will also intelligently start a new line when Enter is pressed after an operator, following keywords like do and while, or when within unclosed brackets.

Auto-indent

Real-time type display

With typeBarEnabled on, ptGHCi shows the type of the identifier under the cursor in real-time while you type. Also shows the types of tab-completed suggestions.

Type bar

Tab completion

In a menu, with the ability to cycle through options with <Tab>

Tab completion

Edit command in external editor

ptGHCi prompt not powerful enough for you? Press <F2> to edit the current entry at the prompt in an external editor of your choosing.

External editor

Show and re-run command history

Use the %past magic command to list prior commands entered into the prompt during the current session, and %rerun to rerun past commands. Useful for restoring bindings after a :reload.

Command history

Installation

ptGHCi requires ZeroMQ, PCRE, and Python 3.3+. You will also need the pkg-config tool and Python's pip package manager for the installation process.

Use stack to install the ptghci binary on your $PATH:

git clone https://github.com/litxio/ptghci
cd ptghci
pip3 install -r pybits/requirements.txt
stack install

Usage and configuration

Just run ptghci to start a session; any command line arguments will be passed to GHCi. The command used to start GHCi can be set via the ghciCommand setting in the configuration file. By default it is stack ghci if stack is on $PATH, otherwise just ghci.

ptGHCi uses a yaml configuration file, which it will look for in the following locations in order of decreasing priority:

./ptghci.yaml
./.ptghci.yaml
$HOME/.ptghci.yaml

The file ptghci.yaml.defaults lists the available options and their defaults.

Magic commands

Special "magic" commands understood by ptGHCi start with % by default:

%past [-n N]: Lists the prior commands entered into the prompt during the current session. Use %past -n N to list up to N past commands, including commands from prior sessions.
%rerun <lines or ranges>: Re-runs past commands, provided as a line number, range, or comma-separated list of line numbers (prefixed by 'p' for history from past sessions) and ranges. Example: %rerun 3,4-5,p8,p23-p24
%hoogle <identifier>: Runs hoogle for the identifier
%style [style_name]: Without an argument, lists the available styles with sample code. With an argument, sets the style to the given style name.

If you find it annoying to have to distinguish between : GHCi commands and '%' ptGHCi commands, you can set the magicPrefix configuration option to ":" and use colon for everything.

Known limitations

Reading from STDIN with getLine and the like is not yet supported
Running the GHCi debugger with :trace is not yet supported
GHCi's it variable does not work properly with ptGHCi; in its place we set a variable that.
For Windows support, see here