Add substring function

CHANGELOG.md

@@ -18,6 +18,7 @@ All notable changes to eww will be listed here, starting at changes since versio
 - Add `justify` property to the label widget, allowing text justification (By: n3oney)
 - Add `EWW_TIME` magic variable (By: Erenoit)
 - Add trigonometric functions (`sin`, `cos`, `tan`, `cot`) and degree/radian conversions (`degtorad`, `radtodeg`) (By: end-4)
+- Add `substring` function to simplexpr
 
 ## [0.4.0] (04.09.2022)
 

crates/simplexpr/src/eval.rs

@@ -379,6 +379,18 @@ fn call_expr_function(name: &str, args: Vec<DynVal>) -> Result<DynVal, EvalError
             }
             _ => Err(EvalError::WrongArgCount(name.to_string())),
         },
+        "substring" => match args.as_slice() {
+            [string, start, len] => {
+                let result: String = string
+                    .as_string()?
+                    .chars()
+                    .skip(start.as_i32()?.max(0) as usize)
+                    .take(len.as_i32()?.max(0) as usize)
+                    .collect();
+                Ok(DynVal::from(result))
+            }
+            _ => Err(EvalError::WrongArgCount(name.to_string())),
+        },
         "search" => match args.as_slice() {
             [string, pattern] => {
                 use serde_json::Value;

docs/src/expression_language.md

@@ -47,6 +47,7 @@ Supported currently are the following features:
 	- `matches(string, regex)`: check if a given string matches a given regex (returns bool)
 	- `captures(string, regex)`: Get the captures of a given regex in a string (returns array)
 	- `strlength(value)`: Gets the length of the string
+    - `substring(string, start, length)`: Return a substring of given length starting at the given index
 	- `arraylength(value)`: Gets the length of the array
 	- `objectlength(value)`: Gets the amount of entries in the object
 	- `jq(value, jq_filter_string)`: run a [jq](https://stedolan.github.io/jq/manual/) style command on a json value. (Uses [jaq](https://crates.io/crates/jaq) internally).