exprel

Overview ¶

Package exprel provides a Spreadsheet-like expression evaluator.

// Quick start

import (
  "layeh.com/exprel"
)

data := map[string]interface{}{
  "name": "Tim",
}
expression := `=LOWER(name) & ".jpg"`
filename, err := exprel.String(exprel.Evaluate(expression, exprel.SourceMap(data)))
if err != nil {
  panic(err)
}
// filename = "tim.jpg"

Introduction ¶

All expressions return a single value. Here are a few examples of some valid expressions and their return values:

Expression                        Return value
----------------------------------------------
Hey there                         "Hey there"
1234                              "1234"
=5+5*2                            15
="A" & " " & "B"                  "A B"
=IF(AND(NOT(FALSE());1=1);1+2;2)  3

Expressions with logic must start with an equals sign (=). Otherwise, the evaluated value is simply the source string.

Values ¶

The following values are can be returned by and used in an expression:

string
float64 (number)
bool (boolean)

Sources may also return the following type, which defines a function that can be called from an expression:

func(c *Call) (value interface{}, err error)

Operators ¶

The following operators and built-ins are defined:

                  Usage              Notes
------------------------------------------
Addition          a + b              number
Subtraction       a - b              number
Multiplication    a * b              number
Division          a / b              number
Exponentiation    a ^ b              number
Modulo            a % b              number
Concatenation     a & b              string

Equality          a = b              string, number, boolean
Inequality        a <> b             string, number, boolean
Greater than      a > b              string, number
Greater or equal  a >= b             string, number
Less than         a < b              string, number
Less or equal     a <= b             string, number

Logical AND       AND(bool...)       Operands lazily evaluated
Logical OR        OR(bool...)        Operands lazily evaluated
Logical NOT       NOT(bool)          Operands lazily evaluated

Condition         IF(bool;ANY;ANY)   Lazily evaluated

Boolean true      TRUE()
Boolean false     FALSE()

The following functions are defined as part of Base:

CHOOSE(number index; ANY...) ANY
  Returns the index item of the remaining arguments
TYPE(ANY a) number
  Identifies the type of a. Types are mapped in the following way:
    Number  = 1
    String  = 2
    Boolean = 4

ABS(number a) number
  Returns the absolute value of a.
EXP(number a) number
  Returns e^a.
LN(number a) number
  Returns the natural logarithm of a.
LOG10(number a) number
  Returns the base-10 logarithm of a.
PI() number
  Returns π.
RAND() number
  Returns a random number in the range [0, 1).
SIGN(number a) number
  Returns the sign of a.

CHAR(number...) string
  Returns a string whose code points are given as arguments.
JOIN(string sep; string...) string
  Returns the trailing string arguments concatenated together with sep.
LEFT(string a; number count = 1) string
  Returns the count left-most characters of a.
LEN(string a) number
  Returns the length of a.
LOWER(string a) string
  Returns a with all uppercase characters transformed to lowercase.
MID(string a; number start; number length = 1) string
  Returns length characters of a, starting from start.
REPT(string a; number count) string
  Returns the string a, repeated count times.
RIGHT(string a; number count = 1) string
  Returns the count right-most characters of a.
SEARCH(string needle; string haystack; number start = 1) number
  Returns the position of needle in haystack, starting from start. -1 is
  returned if needle was not found.
TRIM(string a) string
  Returns a with whitespace removed from the beginning and end.
UPPER(string a) string
  Returns a with all lowercase characters transformed to uppercase.