Text replacement show rules

3 files changed, 69 insertions, 3 deletions

diff --git a/src/eval/methods.rs b/src/eval/methods.rs
index b3674dff..363474fb 100644
--- a/src/eval/methods.rs
+++ b/src/eval/methods.rs
@@ -1,8 +1,9 @@
 //! Methods on values.
 
-use super::{Args, StrExt, Value};
+use super::{Args, Regex, StrExt, Value};
 use crate::diag::{At, TypResult};
 use crate::syntax::Span;
+use crate::util::EcoString;
 use crate::Context;
 
 /// Call a method on a value.
@@ -66,6 +67,19 @@ pub fn call(
             _ => missing()?,
         },
 
+        Value::Dyn(dynamic) => {
+            if let Some(regex) = dynamic.downcast::<Regex>() {
+                match method {
+                    "matches" => {
+                        Value::Bool(regex.matches(&args.expect::<EcoString>("text")?))
+                    }
+                    _ => missing()?,
+                }
+            } else {
+                missing()?
+            }
+        }
+
         _ => missing()?,
     };
 
diff --git a/src/eval/str.rs b/src/eval/str.rs
index 3b4349a1..514bf318 100644
--- a/src/eval/str.rs
+++ b/src/eval/str.rs
@@ -1,3 +1,7 @@
+use std::fmt::{self, Debug, Formatter};
+use std::hash::{Hash, Hasher};
+use std::ops::Deref;
+
 use super::{Array, Value};
 use crate::diag::StrResult;
 use crate::util::EcoString;
@@ -35,3 +39,45 @@ impl StrExt for EcoString {
         }
     }
 }
+
+/// A regular expression.
+#[derive(Clone)]
+pub struct Regex(regex::Regex);
+
+impl Regex {
+    /// Create a new regex.
+    pub fn new(re: &str) -> StrResult<Self> {
+        regex::Regex::new(re).map(Self).map_err(|err| err.to_string())
+    }
+
+    /// Whether the regex matches the given `text`.
+    pub fn matches(&self, text: &str) -> bool {
+        self.0.is_match(text)
+    }
+}
+
+impl Deref for Regex {
+    type Target = regex::Regex;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl Debug for Regex {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        write!(f, "regex({:?})", self.0.as_str())
+    }
+}
+
+impl PartialEq for Regex {
+    fn eq(&self, other: &Self) -> bool {
+        self.0.as_str() == other.0.as_str()
+    }
+}
+
+impl Hash for Regex {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.0.as_str().hash(state);
+    }
+}
diff --git a/src/eval/value.rs b/src/eval/value.rs
index ba30348f..fc54cbce 100644
--- a/src/eval/value.rs
+++ b/src/eval/value.rs
@@ -5,7 +5,7 @@ use std::hash::{Hash, Hasher};
 use std::num::NonZeroUsize;
 use std::sync::Arc;
 
-use super::{ops, Args, Array, Dict, Func, RawLength};
+use super::{ops, Args, Array, Dict, Func, RawLength, Regex};
 use crate::diag::{with_alternative, StrResult};
 use crate::geom::{
     Angle, Color, Dir, Em, Fraction, Length, Paint, Ratio, Relative, RgbaColor, Sides,
@@ -641,6 +641,10 @@ dynamic! {
     Dir: "direction",
 }
 
+dynamic! {
+    Regex: "regular expression",
+}
+
 castable! {
     usize,
     Expected: "non-negative integer",
@@ -686,8 +690,10 @@ castable! {
 
 castable! {
     Pattern,
-    Expected: "function",
+    Expected: "function, string or regular expression",
     Value::Func(func) => Pattern::Node(func.node()?),
+    Value::Str(text) => Pattern::text(&text),
+    @regex: Regex => Pattern::Regex(regex.clone()),
 }
 
 #[cfg(test)]