Hascal is a simple, minimalistic, tiny calculator library and program.

• Hascal only understands single-character operators.
• Hascal only understands infix operators.
• Hascal does not understand parantheses.
• _ is hard-coded as single prefix for negating numbers.
• By default, Hascal understands the operators +, -, *, /, ^, and ? (logarithm).
• By default, Hascal understands the constants pi, e, and i.
• Using Hascal as a library, you can add new operators and new constants using a configuration data type.

The hascal executable program is easy to use. In a shell, type:

>>> hascal 1+2-3*4/5^6?7
-1.7263530417152033

Given a configuration, the hascal function similarly evaluates an expression of type String. In a Haskell interpreter like GHCI, type:

>>> hascal def "1+2-3*4/5^6?7"
Right (0.2736469582847967 :+ 0.0)

>>> hascal def "1++2"
Left "Error at \"\"."