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# NimKalc - A math parsing library

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`NimKalc is a simple implementation of a recursive-descent top-down parser that can evaluate`

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`mathematical expressions.`

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`__Disclaimer__: This library is `__in beta__ and is not fully tested yet. It will be soon, though. If you

`find any bugs or issues, please report them so we can fix them and make a proper test suite!`

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`Features:`

- Support for mathematical constants (`pi`, `tau` and `e` right now)

- Supported functions:

` `- `sin`

` `- `cos`

` `- `tan`

` `- `sqrt`

` `- `root` (for generic roots, takes the base and the argument)

` `- `log` (logarithm in base `e` )

` `- `logN` (logarithm in a given base, second argument)

- Parentheses can be used to enforce different precedence levels

- Easy API for tokenization, parsing and evaluation of AST nodes

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## Current limitations

- No equation-solving (coming soon)

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## How to use it

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`NimKalc parses mathematical expressions following this process:`

- Tokenize the input

- Generate an AST

- Visit the nodes

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`Each of these steps can be run separately, but for convenience a wrapper ``eval` procedure has been defined which takes in a string

`and returns a single AST node containing the result of the given expression.`

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## Supported operators

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`Beyond the classical 4 operators (`+`, ``-` , `/` and `*` ), NimKalc supports:

- `%` for modulo division

- `^` for exponentiation

- unary `-` for negation

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## Exceptions

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`NimKalc defines various exceptions:`

- `NimKalcException` is a generic superclass for all errors

- `ParseError` is used when the expression is syntactically invalid

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- `MathError` is used when there is an arithmetical error such as division by 0 or domain errors (e.g. `log(0)` )

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- `EvaluationError` is used when the runtime evaluation of an expression fails (e.g. trying to call something that isn't a function)

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## Design

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`NimKalc treats all numerical values as ``float` to simplify the implementation of the underlying operators. To tell integers

`from floating point numbers the ``AstNode` object has a `kind` discriminant which will be equal to `NodeKind.Integer` for ints

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`and ``NodeKind.Float` for decimals. It is advised that you take this into account when using the library, since integers might

`start losing precision when converted from their float counterpart due to the difference of the two types. Everything should`

`be fine as long as the value doesn't exceed 2 ^ 53, though`

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`__Note__: The string representation of integer nodes won't show the decimal part for clarity`

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`Some other notable design choices (due to the underlying simplicity of the language we parse) are as follows:`

- Identifiers are checked when tokenizing, since they're all constant

- Mathematical constants are immediately mapped to their real values when tokenizing with no intermediate steps or tokens

- Type errors (such as trying to call an integer) are detected statically at parse time

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## String representations

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`All of NimKalc's objects implement the ``$` operator and are therefore printable. Integer nodes will look like `Integer(x)` , while

`floats are represented with ``Float(x.x)` . Unary operators print as `Unary(operator, right)` , while binary operators print as `Binary(left, operator, right)` .

`Parenthesized expressions print as ``Grouping(expr)` , where `expr` is the expression enclosed in parentheses (as an AST node, obviously).

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`Token objects will print as ``Token(kind, lexeme)` : an example for the number 2 would be `Token(Integer, '2')` . Function calls print like `Call(name, args)`

`where ``name` is the function name and `args` is a `seq[AstNode]` representing the function's arguments

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## Example

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`Here is an example of a REPL using all of NimKalc's functionality to evaluate expressions from stdin (can be found at ``examples/repl.nim` )

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````nim`

`import nimkalc/objects/ast`

`import nimkalc/objects/token`

`import nimkalc/parsing/parser`

`import nimkalc/parsing/lexer`

`import nimkalc/objects/error`

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`import strformat`

`import strutils`

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`proc repl() =`

` ## A simple REPL to demonstrate NimKalc's functionality`

` var line: string`

` var result: AstNode`

` var tokens: seq[Token]`

` let lexerObj = initLexer()`

` let parserObj = initParser()`

` let visitor = initNodeVisitor()`

` echo "Welcome to the NimKalc REPL, type a math expression and press enter"`

` while true:`

` try:`

` stdout.write("=> ")`

` line = stdin.readLine()`

` echo `& "Parsing and evaluation of {line} below:"

` tokens = lexerObj.lex(line)`

` # No-one cares about the EOF token after all`

` echo `& "Tokenization of {line}: {tokens[0..^2].join(\", \")}"

` result = parserObj.parse(tokens)`

` echo `& "AST for {line}: {result}"

` result = visitor.eval(result)`

` case result.kind:`

` # The result is an AstNode object, specifically`

` # either a node of type NodeKind.Float or a NodeKind.Integer`

` of NodeKind.Float:`

` echo `& "Value of {line}: {result.value}"

` of NodeKind.Integer:`

` echo `& "Value of {line}: {int(result.value)}"

` else:`

` discard # Unreachable`

` except IOError:`

` echo "\nGoodbye."`

` break`

` except ParseError:`

` echo `& "A parsing error occurred: {getCurrentExceptionMsg()}"

` except MathError:`

` echo `& "An arithmetic error occurred: {getCurrentExceptionMsg()}"

` except OverflowDefect:`

` echo `& "Value overflow/underflow detected: {getCurrentExceptionMsg()}"

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`when isMainModule:`

` repl()`

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`__Note__: If you don't need the intermediate representations shown here (tokens/AST) you can just ``import nimkalc` and use

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`the ``eval` procedure, which takes in a string and returns the evaluated result as a primary AST node like so:

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````nim`

`import nimkalc`

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`echo eval("2+2") # Prints Integer(4)`

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## Installing

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`You can install the package via nimble with this command: ``nimble install nimkalc`

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`__Note__: Nim 1.2.0 or higher is required to build NimKalc! Other versions are likely work if they're not too old, but they have not been tested`