From c5b0ecbfbb73113e99f8baa29891fbe0ba598b68 Mon Sep 17 00:00:00 2001
From: Melody Horn <melody@boringcactus.com>
Date: Mon, 5 Apr 2021 11:58:17 -0600
Subject: implement function `subst`

---
 src/makefile/functions.rs | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/src/makefile/functions.rs b/src/makefile/functions.rs
index 6e9d3cb..46caca5 100644
--- a/src/makefile/functions.rs
+++ b/src/makefile/functions.rs
@@ -16,6 +16,10 @@ pub fn expand_call(
     to_eval: Option<Rc<RefCell<Vec<String>>>>,
 ) -> Result<String> {
     match name {
+        "subst" => {
+            assert_eq!(args.len(), 3);
+            text::subst(macros, &args[0], &args[1], &args[2])
+        }
         "strip" => {
             assert_eq!(args.len(), 1);
             text::strip(macros, &args[0])
@@ -123,6 +127,18 @@ pub fn expand_call(
 mod text {
     use super::*;
 
+    pub fn subst(
+        macros: &MacroSet,
+        from: &TokenString,
+        to: &TokenString,
+        text: &TokenString,
+    ) -> Result<String> {
+        let from = macros.expand(from)?;
+        let to = macros.expand(to)?;
+        let text = macros.expand(text)?;
+        Ok(text.replace(&from, &to))
+    }
+
     pub fn strip(macros: &MacroSet, text: &TokenString) -> Result<String> {
         let text = macros.expand(text)?;
         // TODO don't allocate this vec
-- 
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