Syntax

The MEL supports all the key syntactic constructions: variables, operations, loop statements, etc.

The language itself is entirely lower case.

The following examples are based on a result feed named persons that has an entry with the following metas:

  • name: roger

  • age: 42

  • ${feeds["person"].metas["name"]}: roger, bruce

This page discusses:

See Also
About Mashup Expression Language
Handling Categories, Facets and entries

Simple variables

A variable represents a specific data item, or value, and acts as a placeholder for that value. When a formula encounters a variable, the formula searches for the value of the variable and uses it in the formula.

The basic syntax is: ${my.variable}

Table 1. Simple expression examples

Expression

Result

hello ${feeds["person"].metas["name"]}

hello roger

hello ${feeds["person"].metas["unknown_meta"]}

hello

hello \${feeds["person"].metas["name"]}

hello ${feeds["person"].metas["name"]}

Fallbacks

You can declare variable fallbacks using pipes |

  • ${my.variable|other.variable}

  • ${my.variable|other.variable|last.variable}

  • ${my.variable|"hardcoded fallback text"}

Table 2. Fallback/Advanced expression examples

Expression

Result

hello ${feeds["person"].metas["name"]|"world"}

hello roger

hello ${feeds["person"].metas["unknown_meta"]|"world"}

hello world

hello ${feeds["person"].metas["unknown_meta"]|feeds["person"].metas["name"]|"world"}

hello roger

hello ${feeds["person"].metas["unknown_meta"]|feeds["person"].metas["unknown_meta2"]|"world"}

hello world

hello ${feeds["person"].metas["unknown_meta"]|feeds["person"].metas["unknown_meta2"]}

hello

Dynamic variables and functions

Dynamic variables are variables whose values are determined when the program is run.

  • ${i18n["machine_"+robot.id]}

  • ${math:${op.sum}(1,1)}

Table 3. Dynamic expression examples

Expression

Result

${fn:${feeds["person"].metas["name"]}(${feeds["person"].metas["age"]})} = ${fn:roger(42)}

result of the function roger passing the parameter 42

Operations

  • Strings: ${my.age == "42"}

  • Supported numerical operators: - + * / % == != < > ( ) ^ >= <= Example: ${(2+3)*4} = 20

  • Supported string operators: == !=

  • Logical operators: ${(2 <= 3 && 42 != 21) || 3 >= 3} where && = and || = OR

  • Brackets support:

    • ${page.params["q"][1]}

    • ${math:sum(1,1)[0]}

  • Concatenation and sum: + is the concatenation operator (as in Java) and also the sum operator for numerical operations.

    • ${"5" + "6"} --> 11

    • ${"a" + "b"} --> ab

    • ${"a" + "5"} --> " (it will be resolved to NaN+5)

    • ${str:join(","a","5")} --> a5

Table 4. Operation examples

Expression

Result

i am ${feeds["person"].metas["age"]}

i am 42

i am ${feeds["person"].metas["age"] + 10}

i am 52

i am ${feeds["person"].metas["age"] / 2}

i am 21

i am ${feeds["person"].metas["age"] % 40}

i am 2

i am ${feeds["person"].metas["age"] * 2}

i am 84

i am ${feeds["person"].metas["age"] - 20}

i am 22

i am ${feeds["person"].metas["age"] + 10.0}

i am 52.0

i am ${feeds["person"].metas["age"] / 2.0}

i am 21.0

i am ${feeds["person"].metas["age"] % 40.0}

i am 2.0

i am ${feeds["person"].metas["age"] * 2.0}

i am 84.0

i am ${feeds["person"].metas["age"] - 20.0}

i am 22.0

i am ${feeds["person"].metas["age"] == "42"}

i am true

i am ${feeds["person"].metas["age"] == "24"}

i am

i am ${feeds["person"].metas["age"] != "42"}

i am

i am ${feeds["person"].metas["age"] != "24"}

i am true

i am ${feeds["person"].metas["age"] == "roger"}

i am true

i am ${feeds["person"].metas["age"] == "robert"}

i am

i am ${feeds["person"].metas["age"] != "roger"}

i am

i am ${feeds["person"].metas["age"] != "robert"}

i am true

${feeds["person"].metas["age"][0]}

roger

${feeds["person"].metas["age"][1]}

bruce

${feeds["person"].metas["age"][1][0]}

b

${feeds["person"].metas["age"][1][2]}

u

${"world"[1]}

o

${("hello" + "world")[8]}

l
Table 5. Logical operation examples

Expression

Result

I am ${Roger && 42}

false

I am ${Roger || 42}

true

I am ${Roger || (42 && Roger)}

false

Functions

MEL Functions are classified by categories under the following namespaces:

  • category functions: className, url.

  • currency: format.

  • date: addDays, addYears, addMilliseconds, addMonths, addMinutes, addHours, addSeconds, addWeeks, now, format, elapsedTime.

  • entry: cleanId, previewHtmlUrl, thumbnailUrl, downloadUrl, previewImageUrl.

  • list: join, size.

  • math: min, atan, max, pow, asin, cos, ceil, sqrt, random, log2, sum, round, divide, multiply, log, subtract, exp, abs, floor, sin, avg, tan, acos.

  • number: format.

    Note: For number approximation, we use the rounding modes described in https://docs.oracle.com/javase/7/docs/api/java/math/RoundingMode.html

  • str (string): replace, lowerCase, abbreviate, upperCase, length, hashCode, split, contains, trim, substr.

  • var: get, set.

    Note: The fn namespace is used as the standard namespace.

Function calls:

  • Simple: ${date:now()}

  • With arguments: ${str:substr("toto", 2)}

  • With variable arguments: ${math:max(${my.age}, ${your.age})}

Table 6. Function expression examples

Expression

Result

I am ${math:substr(page.params["name"], 0, 3)}

I am rog

${number:format(0.25, 1, 4, 1, 1, true, "HALF_UP")}

0.3

Internationalization functions

  • ${user:locale(MELHttpServletRequest request)} returns the locale used by the current user from the HTTP query.

  • ${date:format(MELString date, MELString pattern, MELString locale, MELString timeZone)} returns the date formatted as the output pattern using the specified locale and timezone.

  • ${i18n:message(MELHttpServletRequest request, MELType code) translates a string like ${i18n[code]} but using the locale from the HTTP query.

  • ${i18n:message(MELHttpServletRequest request, MELType code, MELType[]... parameters) translates a string containing variable parts (specified by {0}, {1}, etc.) which are replaced by the values in parameters.

Sample usage:

${user:locale(request)}
> en
${date:format(${entry.metas['date']}, 'dd/MM/yyyy hh:mm:ss', 'en_EN', 'GMT')
> 10/02/2014 12:30:10
${date:format(${entry.metas['date']}, "MM/dd/yyyy hh:mm:ss", "en_US", "GMT-5")}
> 02/10/2014 07:30:10

In localization file (*.properties):

error.message=Error code: {0}

document.summary=created by {0} on {1} at {2}

In the Mashup Builder:

${i18n:message(request, 'error.message', '404')}
> Error code: 404
${i18n:message(request, 'document.summary', author, date, time)}
> created by John Doe on February 10, 2014 at 10:30am

Combinations

  • Operations and functions: ${math:max(${my.age}, ${your.age}) + 10}

Ternaries

  • Simple: ?{true?yes:no}

  • Advanced: ?{${persons.age}?i am ${persons.age / 2}:age not found}

  • Short syntax: ?{true?:no}

  • Nested: ?{true?{true?nested yes:nested no}:no}

    Table 7. Ternary expression examples

    Expression

    Result

    ?{feeds["person"].metas["name"]?meta exists:meta not found}

    meta exists

    ?{feeds["person"].metas["unknown_meta"]?meta exists:meta not found}

    meta not found

    ?{feeds["person"].metas["age"]?i am feeds["person"].metas["age"]/2:age not found}

    i am 21

    ?{true?yes:no}

    yes

    ?{yes:no}

    no

    ?{true?:no}

    -

    ?{true?{true?nested yes:nested no}:no}

    nested yes

    ?{true?{?nested yes:nested no}:no}

    nested no

    ${if feeds["person"].metas["name"] != "roger"} wrong ${elseif math:sum(1,1) ==3} wrong ${elseif math:sum(1,1) == 2} happy ${else} wrong ${/if}

    happy
    Table 8. Special ternary expression examples

    Expression

    Result

    hello ${page.params["name"]}

    hello roger

    hello ${page.params["unknown_meta"]}

    hello

    hello ?{page.params["name"]?no otherwise}

    hello no otherwise

    hello ?{page.params["unknown_meta"]?no otherwise}

    -

If statements

The If statement enables you to evaluate a sequence of statements if a condition is true and evaluate a different sequence of statements if it is not true.

  • You are ${if page.params["n"] != 42} wrong ${elseif math:sum(1,1) ==3} wrong ${elseif math:sum(1,1) == 2} happy ${else} wrong ${/if}

Foreach loop statements

Foreach loops enable you to evaluate a sequence of statements multiple times.

  • ${foreach 1,2,3} ${loop.element}?{$loop.hasNext}?,} ${/foreach} go!

  • ${foreach number in 1,2,3} ${number}?{${loop.hasNext}?,} ${/foreach} go!

Table 9. Loop expression examples

Expression

Result

${foreach page.params["name"]}I am ${loop.element}${/foreach}

I am roger

${foreach "a", "b", "c"}${loop.element}${/foreach}

abc

${foreach 1,2,3}and ${loop.index} ${/foreach}

and 0 and 1 and 2

${foreach 1,2,3}and ${loop.element} ${/foreach}

and 1 and 2 and 3

${foreach number in 1,2,3} and ${number} ${/foreach}

and 1 and 2 and 3

Flags

  • !m --> HTML escaping

  • !x --> XML escaping. For example: ${entry.metas['text']!+x}

  • !u --> URL encoding. This flag is useful to declare URLs.

  • !h --> Highlighting (only available for metas). For example: ${entry.metas["title"]!h}

Important: We recommend declaring whether flags must be used or not specifically, with the + and - signs. For example: !+h or !+h-x Without the + and - signs, the default behavior is inverted.

Code samples

The two following code samples using MEL can be pasted in an HTML widget. They both contain typical iteration made with foreach statements. 

<h1>Iterate over entries</h1>
<ul>
${foreach hit in feed.entries}
    <li>
        <h1>${hit.title}</h1>
        <a href="${entry:downloadUrl(hit, request, '<Page name>')}">Download</a>
        <iframe src="${entry:previewHtmlUrl(hit, request, '<Page name>')}"></iframe>
        <img src="${entry:previewImageUrl(hit, request, '<Page name>')}" />
    </li>
${/foreach}
</ul>
<h1>Iterate over the author facet</h1>
<ul>
${foreach catElement in feeds[’cloudview’].facets[’author’].leaves}
    <li>
        <a href="${category:url(catElement, request, feeds[’cloudview’])}" 
class="${category:className(catElement)}">
            ${i18n[catElement]}
        </a>
    </li>
${/foreach}
</ul>
Note: request refers to the request variable available in any context.