Hascal is both a simple but extendable calculator library for Haskell and a command-line program using it.
Also, its source code is a nice example for a minimalistic Haskell project.
Some examples for the usage of the command-line program:
Also, preceding exclamation marks mean that the following number is imaginary, that is, you have to multiply it with i. E.g.:
hascal _1 ^ 0.5!1.0
And as you can see, negative numbers are preceded by a underscore.
Although hascal itself doesn't understand brackets, you can use your shell to get that functionality, like this (using bash):
hascal e ^ $(hascal i*pi)-1.0
Speaking of shells, you should consider that your shell might extend an asterisk (*) to the files at the current directory, like here:
echo *_darcs dist hascal.cabal Hascal.hs LICENSE Main.hs README.org Setup.hs
That's why this might not work:
hascal 1 * 2Error. :(
But you could do this instead:
Yeah, that's it. Hascal is really minimalistic. And I'm not planning to extend it much.
- data Complex a
- operators :: RealFloat t => [(Char, Complex t -> Complex t -> Complex t)]
- eval :: (Read t, RealFloat t) => [(Char, Complex t -> Complex t -> Complex t)] -> String -> Maybe (Complex t)
- hascal :: (Read t, RealFloat t) => String -> Maybe (Complex t)
- prettyPrint :: (Show t, RealFloat t) => Complex t -> String
Just re-exporting the
Complex data-type for simplicity and comfort.
data Complex a
Complex numbers are an algebraic type.
operators is the default list of operators.
An operator consists of one character and a function with of type
Number -> Number -> Number.
- addition, represented by
- subtraction, represented by
- multiplication, represented by
- division, represented by
- exponentiation, represented by
- logarithming (with flipped arguments, see below), represented by
such that these laws are held:
(a - b == c) == (a == b + c) (a / b == c) == (a == b * c) (a ? b == c) == (a == b ^ c)
|:: (Read t, RealFloat t)|
|=> [(Char, Complex t -> Complex t -> Complex t)]|
list of operators
string containing term
|-> Maybe (Complex t)|
just result, or nothing
eval gets a list of operators and a string containing a mathematical
expression/term which only uses those operators listed in the first
argument, and returns the result of that term.