42 lines
1.3 KiB
Markdown
42 lines
1.3 KiB
Markdown
mathexpr []()
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========
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Ever wanted to take as input a mathematical expression to fill in values and use it? `mathexpr` is exactly what you need.
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_I also wrote this in JavaScript some time ago: [Equation](https://github.com/mdibaiee/Equation)_
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Examples
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--------
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Simple evaluation of expressions:
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```haskell
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import Data.MathExpr
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main = do
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expr <- getLine -- a mathematical expression, e.g. sin x + y ^ 2
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-- replace x and y with the specified values and evaluate: sin 2 + 5 ^ 2 = 25.909..
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print $ evaluate def expr [("x", 2), ("y", 5)]
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```
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Using custom operators and functions:
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```haskell
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import Data.MathExpr
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-- operators are in the form (character, precedence, function)
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-- example: ('+', 0, (+)), ('*', 1, (*))
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-- the function should have the type (Double -> Double -> Double)
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-- the higher the precedence, the sooner the operator operates
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-- functions are in the form (name, function)
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-- example: ("ln", log)
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-- the function should have the type (Double -> Double)
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main =
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let avg a b = (a + b) / 2
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let settings = Settings { operators = defaultOperators ++ [('~', 0, avg)]
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, functions = defaultFunctions ++ [("trunc", fromIntegral . truncate)]
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evaluate settings "3 ~ 5" [] -- 4
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evaluate settings "trunc 1.1" [] -- 1
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```
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