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expressions.md

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Sempare Template Engine

Copyright (c) 2019-2024 Sempare Limited

Expressions

You can use different types of expressions.

Conditional expressions:

<% a := 10 %>
<% if a + 1 < 10 %>
<% end %>

Comparison expressions ( =, <>, <, <=, >, >= ) work on numeric and string values.

Numeric operators (+, -, /, *, mod) work on numeric values. The + operator also works on strings so you can append values.

Futher, == is an alias for =, and != is an alias for <>.

The special _ variable

A special variable _ (underscore) is defined to allow access to the variable/record/class passed into the template evaluator.

<% for i in _ %> <% i %><% end %>

The following Delphi code illustrates the usage:

begin
  var l := TList<string>.Create;
  l.AddRange(['1','2','3']);
  Assert.IsEqual('123', Template.Eval('<% for v in _ %><% v %><% end %>', l));
  L.Free;
end;

If the variable is not found, the variable will be referenced on _.

This means that <% a %> will be the same as <% _.a %>.

Strings

Strings can be single quote or double quotes. There is no special meaning on either. The backslash can be used for escaping.

<% 'that\'s nice' %>
<% "that's nice" %>

Arrays

Arrays can be defined with square braces. e.g.

<% arr := [ 1, 2, 3] %>

There is no requirement for the values to be of the same type.

<% arr := [ 1, false, "string" ] %>

Dereferencing an array is 0 based. e.g.

num := arr[0];
bool := arr[1];
str := arr[2];

Also see the for-in/for-of loop statements.

In the above, the for-in statement will return 1, 2, 3 In the above, the for-of statement will return 1, false, "string"

Maps

Simple map / dictionary support is provided. You may define a map withing curly braces. e.g.

<% map := { 
        "a" : 1, 
        "b": true, 
        "c": "string", 
        "d": { 
            "key" : "value" 
        } 
  } %>

Note again that there is no requirement for the types to be of the same type.

Dereferencing a map is as follows:

<% key := map['a'] %> // or
<% key := map.a %>    // for keys without spaces and match the identifier syntax

Also see the for-in/for-of loop statements.

In the above, the for-in statement will enumerate over the keys. In the above, the for-of statement will enumerate over the values.

NOTE Values in a map are immutable. This means that you need to recreate the entire map if you need to change a value.

This is currently due to a limitation in the assignment statement implementation which currently assigns simple variables only. We will review this in future.