bittybox

README

bittybox | Simple floating point calculator

bittybox is a small, underpowered floating point expression evaluator.

Motivation

Performing safe, efficient user-supplied math operations.

Features

Basic operators (+-*/^), grouping, predictable operator precedence, variables, some constants and common unary functions (sin, cos, etc).

Grammar

Expr --> Unit (Binary Unit)*
Unit --> Number | "(" Expr ")" | "-" Unit | Ident
Binary --> "+" | "-" | "*" | "/" | "^"

Some Credits

Initial inspiration from the long abandoned https://github.com/marcak/calc/tree/master/

With advice from https://www.engr.mun.ca/~theo/Misc/exp_parsing.htm

Documentation

Index

• func Evaluate(formula string, vars ...Var) (float64, error)
• type ErrInvalidSyntax
  • func (e ErrInvalidSyntax) Error() string
• type ErrUnboundVars
  • func (e ErrUnboundVars) Error() string
• type Expr
  • func CompileExpr(formula string, varNames ...string) (Expr, error)
  • func (e *Expr) Evaluate(vals []float64) float64
• type Float
• type Var

Examples

• CompileExpr
• Evaluate

Functions

func Evaluate

func Evaluate(formula string, vars ...Var) (float64, error)

Compute will compile and evaluate an expression.

Example

package main

import (
	"fmt"

	"github.com/ischneider/bittybox"
)

func main() {
	fmt.Println(bittybox.Evaluate("5 + y", bittybox.Var{"y", 1}))
}

Output:

6 <nil>

Types

type ErrInvalidSyntax

type ErrInvalidSyntax struct {
	Message string
	Line    int
	Column  int
}

ErrInvalidSyntax describes an invalid expression.

func (ErrInvalidSyntax) Error

func (e ErrInvalidSyntax) Error() string

type ErrUnboundVars

type ErrUnboundVars struct {
	Missing []string
}

ErrUnboundVars is returned when an expression is missing variables.

func (ErrUnboundVars) Error

func (e ErrUnboundVars) Error() string

type Expr

type Expr struct {
	// contains filtered or unexported fields
}

Expr is a compiled expression that can be reused serially.

func CompileExpr

func CompileExpr(formula string, varNames ...string) (Expr, error)

CompileExpr compiles the provided forumula into an Expr.

Example

package main

import (
	"fmt"

	"github.com/ischneider/bittybox"
)

func main() {
	expr, err := bittybox.CompileExpr("5 + y", "y")
	if err != nil {
		panic(err)
	}
	fmt.Println(expr.Evaluate([]float64{10}))
}

Output:

15

func (*Expr) Evaluate

func (e *Expr) Evaluate(vals []float64) float64

Compute evaluates the expression with the provided values. Values must be provided in the order of their corresponding varNames.

type Float

type Float interface {
	float32 | float64
}

type Var

type Var struct {
	Name  string
	Value float64
}

Var is a name, value pair.