A simple DSL for calculating dates, with a toplevel interpreter implemented in Haskell
.
No, unfortunately, this is not about dating.
S ::= DATE | DATE NUMOP YMD | DATE DIFF DATE
NUMOP ::= + | -
DIFF ::= <>
DATE ::= YMD | TODAY
A dater
program consists of just one command: adding dates or finding the difference two dates.
Each date consists of a year, month, and a day.
The add +
operator takes a y/m/d
date and a y/m/d
date shift to produce a new date.
dater $> 2000/3/2 + 1/0/3
2001/3/5
The add -
operator takes a y/m/d
date and a y/m/d
date shift to produce a new date.
When today
is 2022/11/19:
dater $> today - 0/22/33
2020/12/17
The difference <>
operator will find the distance between two dates.
dater $> 2021/11/12 <> 2022/1/1
0/1/20
Five syntactic sugar functions exist to make the dater
easier to use.
* day x => 0 0 x
* week y => 0 0 7y
* month z => 0 z 0
* year w => w 0 0
* today => today's date
Example:
dater $> 2012/12/22 + week 10
2013/3/2
The recommended way to use the language is with the toplevel interpreter in this repository.
First, you will need The Haskell Stack. Then, simply run
stack install
This will copy the dater
binary to your path (~/.local/bin/
on Linux systems).
โ ~ dater
Welcome to dater, date calculations done easy!
Example Usages:
dater $> today + week 9
dater $> 2022/11/22 - 0/11/1
dater $> today <> 1997 / 4 / 10
dater $>
When you are done, exit with
dater $>:q
Goodbye.
- Use previous computation value (Python's
_
or ghci'sit
) - Run files instead of running the REPL, e.g.
dater foo.dtr
- Option to specify as days:
as_days today <> 1997/4/10
. This could be a toggle option.
- Better
mtl
instead ofIO (Either DateError a)
- Migrate
Main.hs
out ofInputT