# #`=` (arithmetic evaluation)

Evaluate a mathematical function (deprecated)

## # Description

`=` evaluates a mathematical function and returns it's output

This is a deprecated feature. Please refer to `expr` instead.

## # Usage

``````<stdin> -> = evaluation -> <stdout>

= evaluation -> <stdout>
``````

## # Examples

As a method:

``````Â» let age=18
Â» \$age -> = < 21
true

Â» \$age -> = < 21 -> if { out "Under 21" } else { out "Over 21" }
Under 21
``````

As a function:

``````Â» let age=18
Â» = age < 21
true

Â» = age < 21 -> if { out "Under 21" } else { out "Over 21" }
Under 21
``````

Inlining as a function:

``````Â» let age=18
Â» if { = age < 21 } then { out "Under 21" } else { out "Over 21" }
Under 21
``````

## # Detail

### # Variables

There are two ways you can use variables with the math functions. Either by string interpolation like you would normally with any other function, or directly by name.

String interpolation:

``````Â» set abc=123
Â» = \$abc==123
true
``````

Directly by name:

``````Â» set abc=123
Â» = abc==123
false
``````

To understand the difference between the two, you must first understand how string interpolation works; which is where the parser tokenised the parameters like so

``````command line: = \$abc==123
token 1: command (name: "=")
token 2: parameter 1, string (content: "")
token 3: parameter 1, variable (name: "abc")
token 4: parameter 1, string (content: "==123")
``````

Then when the command line gets executed, the parameters are compiled on demand similarly to this crude pseudo-code

``````command: "="
parameters 1: concatenate("", GetValue(abc), "==123")
output: "=" "123==123"
``````

Thus the actual command getting run is literally `123==123` due to the variable being replace before the command executes.

Whereas when you call the variable by name it's up to `=` or `let` to do the variable substitution.

``````command line: = abc==123
token 1: command (name: "=")
token 2: parameter 1, string (content: "abc==123")
``````
``````command: "="
parameters 1: concatenate("abc==123")
output: "=" "abc==123"
``````

The main advantage (or disadvantage, depending on your perspective) of using variables this way is that their data-type is preserved.

``````Â» set str abc=123
Â» = abc==123
false

Â» set int abc=123
Â» = abc==123
true
``````

Unfortunately is one of the biggest areas in Murex where you'd need to be careful. The simple addition or omission of the dollar prefix, `\$`, can change the behavior of `=` and `let`.

### # Strings

Because the usual Murex tools for encapsulating a string (`"`, `'` and `()`) are interpreted by the shell language parser, it means we need a new token for handling strings inside `=` and `let`. This is where backtick comes to our rescue.

``````Â» set str abc=123
Â» = abc==`123`
true
``````

Please be mindful that if you use string interpolation then you will need to instruct `=` and `let` that your field is a string

``````Â» set str abc=123
Â» = `\$abc`==`123`
true
``````

### # Best practice recommendation

As you can see from the sections above, string interpolation offers us some conveniences when comparing variables of differing data-types, such as a `str` type with a number (eg `num` or `int`). However it makes for less readable code when just comparing strings. Thus the recommendation is to avoid using string interpolation except only where it really makes sense (ie use it sparingly).

### # Non-boolean logic

Thus far the examples given have been focused on comparisons however `=` and `let` supports all the usual arithmetic operators:

``````Â» = 10+10
20

Â» = 10/10
1

Â» = (4 * (3 + 2))
20

Â» = `foo`+`bar`
foobar
``````

Murex uses the govaluate packageopen in new window. More information can be found in it's manual.

• `=`