Add range_select function to simple expr

Fixes elkowar#622

crates/simplexpr/src/dynval.rs

@@ -1,7 +1,13 @@
 use eww_shared_util::{Span, Spanned};
 use itertools::Itertools;
 use serde::{Deserialize, Serialize};
-use std::{convert::TryFrom, fmt, iter::FromIterator, str::FromStr};
+use std::{
+    convert::TryFrom,
+    fmt,
+    iter::FromIterator,
+    ops::{Bound, RangeBounds},
+    str::FromStr,
+};
 
 pub type Result<T> = std::result::Result<T, ConversionError>;
 
@@ -232,6 +238,23 @@ impl DynVal {
             .cloned()
             .ok_or_else(|| ConversionError { value: self.clone(), target_type: "json-object", source: None })
     }
+
+    pub fn as_range(&self) -> Result<(Bound<f64>, Bound<f64>)> {
+        let range = self.as_string()?;
+        let Some((from, to)) = range.split_once("..") else {
+            return Err(ConversionError { value: self.clone(), target_type: "range", source: None })
+        };
+        let from = match from {
+            "" => Bound::Unbounded,
+            v => DynVal::from_str(v)?.as_f64().map(Bound::Included)?,
+        };
+        let to = match to {
+            "" => Bound::Unbounded,
+            v if v.starts_with('=') => DynVal::from_str(&v[1..])?.as_f64().map(Bound::Included)?,
+            v => DynVal::from_str(v)?.as_f64().map(Bound::Excluded)?,
+        };
+        Ok((from, to))
+    }
 }
 
 #[cfg(test)]

crates/simplexpr/src/eval.rs

@@ -8,6 +8,7 @@ use eww_shared_util::{Span, Spanned, VarName};
 use std::{
     collections::HashMap,
     convert::{TryFrom, TryInto},
+    ops::RangeBounds,
 };
 
 #[derive(Debug, thiserror::Error)]
@@ -33,6 +34,10 @@ pub enum EvalError {
     #[error("Unable to index into value {0}")]
     CannotIndex(String),
 
+    // TODO useful error variant?
+    #[error("Function {0} failed: {1}")]
+    FunctionError(&'static str, String),
+
     #[error("Json operation failed: {0}")]
     SerdeError(#[from] serde_json::error::Error),
 
@@ -341,6 +346,31 @@ fn call_expr_function(name: &str, args: Vec<DynVal>) -> Result<DynVal, EvalError
             [json] => Ok(DynVal::from(json.as_json_object()?.len() as i32)),
             _ => Err(EvalError::WrongArgCount(name.to_string())),
         },
+        "range_select" => match args.as_slice() {
+            [value, map] => {
+                let value = value.as_f64()?;
+                let map = map.as_json_array()?;
+                for mapping in map {
+                    let mapping = DynVal::from(&mapping);
+                    let array = mapping.as_json_array()?;
+                    let [range, result] = array.as_slice() else {
+                        // TODO what error to use here
+                        // TODO we could also add `DynVal::as_tuple<const LENGTH: usize>()`
+                        return Err(ConversionError{
+                            value: mapping,
+                            target_type: "[string, string]",
+                            source: None
+                        }.into())
+                    };
+                    let range = DynVal::from(range).as_range()?;
+                    if range.contains(&value) {
+                        return Ok(result.into());
+                    }
+                }
+                Err(EvalError::FunctionError("range_select", format!("No entry matched value: {value}")))
+            }
+            _ => Err(EvalError::WrongArgCount(name.to_string())),
+        },
 
         _ => Err(EvalError::UnknownFunction(name.to_string())),
     }

rust-toolchain.toml

@@ -1,4 +1,4 @@
 [toolchain]
-channel = "nightly-2022-08-27"
+channel = "nightly-2022-11-25"
 components = [ "rust-src" ]
 profile = "default"