Epitech project - funEvalExpr

An expression evaluator written in Haskell.

Goal

Implement a program which is able to parse a string given as argument, evaluate it and display the result.

Must

• Handle float numbers ans parentheses.
• Handle addition, subtraction, multiplication, division and power operators (+ - * / ^).
• The output must always have two digits after the decimal points (examples: 1.00, 3.14).
• Implement a recursive descent parser with combinators, following a Parsing Expression Grammar (PEG).

Example

Build with make and stack:

$ make
or
$ stack build --copy-bins

And run with:

$ ./funEvalExpr "3 + 5.34"
8.34
$ ./funEvalExpr "(0.345+5)*(-2-1)/3"
-5.35

Features

Operands format

(?:\d+)|(?:\d*\.?\d*)

Valid operands can be:

• 42
• 42.42
• 42.
• .42
• .

Operators

Binary Operators

Operator	Aka	Precedence	Description
e	Exp	120	Scientific exponentiation
^	Pow	120	Exponentiation
*	Mul	100	Multiplication
/	Div	100	Division
%	Mod	100	Modulo
+	Add	95	Addition
-	Sub	95	Subtraction
>	Gt	80	Greater than
<	Lt	80	Less than
>=	Ge	80	Greater than or equal to
<=	Le	80	Less than or equal to
==	Eq	80	Equal to
!=	Ne	80	Not equal to
&&	And	75	Logical AND
||	Or	70	Logical OR

Unary operators

Operator	Aka	Description
+	Pos	Identity
-	Neg	Negation
!	Not	Logical negation

Debug

With -d option, the program will print the AST of the expression.

$ ./funEvalExpr -d "(0.345+5)*(-2-1)/3"
Div(
    Mul(
        Add(
            0.345,
            5.0
        ),
        Sub(
            Neg(
                2.0
            ),
            1.0
        )
    ),
    3.0
)