From 4daf7b149622a16a2271630a19f0833702477a86 Mon Sep 17 00:00:00 2001
From: Joel Kronqvist <joel.kronqvist@iki.fi>
Date: Sat, 16 Aug 2025 03:25:45 +0300
Subject: feat: vector concatenation

---
 src/parse/parsetree.rs |  1 +
 src/sexp/display.rs    |  1 +
 src/sexp/mod.rs        |  1 +
 src/sexp/step.rs       | 21 +++++++++++++++++++++
 src/type/check.rs      |  7 +++++++
 5 files changed, 31 insertions(+)

diff --git a/src/parse/parsetree.rs b/src/parse/parsetree.rs
index bd15e79..c773f3b 100644
--- a/src/parse/parsetree.rs
+++ b/src/parse/parsetree.rs
@@ -119,6 +119,7 @@ fn tokens_to_ast_inner(
             Some(Sym(s)) if s == "false"  => Ok(Atom(False)),
 	    Some(Sym(s)) if s == "quote"  => Ok(Atom(Quote)),
 	    Some(Sym(s)) if s == "vector" => Ok(Atom(Vector)),
+	    Some(Sym(s)) if s == "<>"     => Ok(Atom(Concat)),
 	    Some(Sym(s)) if s == "print"  => Ok(Atom(Print)),
 	    Some(Sym(s)) if s == "let"    => Ok(Atom(Let)),
 	    Some(Sym(s)) if s == "fn"     => Ok(Atom(Fun)),
diff --git a/src/sexp/display.rs b/src/sexp/display.rs
index e2f4ffc..ec1b421 100644
--- a/src/sexp/display.rs
+++ b/src/sexp/display.rs
@@ -28,6 +28,7 @@ impl fmt::Display for SLeaf {
 	    RestPat(s) => format!("..{s}"),
             Quote  => "quote".to_string(),
             Vector => "vector".to_string(),
+            Concat => "<>".to_string(),
 	    Print  => "print".to_string(),
             Let    => "let".to_string(),
 	    Fun    => "fn".to_string(),
diff --git a/src/sexp/mod.rs b/src/sexp/mod.rs
index aa51811..1a90f52 100644
--- a/src/sexp/mod.rs
+++ b/src/sexp/mod.rs
@@ -30,6 +30,7 @@ pub enum SLeaf {
     Or,
     Not,
     Xor,
+    Concat,
 
     Quote,
     Vector,
diff --git a/src/sexp/step.rs b/src/sexp/step.rs
index 9077401..59b201c 100644
--- a/src/sexp/step.rs
+++ b/src/sexp/step.rs
@@ -441,6 +441,27 @@ impl SExp {
 	    },
 
 
+	    // Concatenation
+	    SCons(op, l) if *op == Atom(Concat) => {
+		let ls = l.parts();
+		let firstvec = ls.get(0).unwrap();
+		let secondvec = ls.get(1).unwrap();
+		let firstvec = match firstvec {
+		    SCons(a, b) if **a == Atom(Vector) => *b.clone(),
+		    t => t.clone(),
+		};
+		let secondvec = match secondvec {
+		    SCons(a, b) if **a == Atom(Vector) => *b.clone(),
+		    t => t.clone(),
+		};
+		let mut res = Atom(Nil);
+		for exp in firstvec.parts().into_iter().chain(secondvec.parts()).rev() {
+		    res = scons(exp, res);
+		}
+		Ok(scons(Vector, res))
+	    },
+
+
             // Arithmetic
 
 
diff --git a/src/type/check.rs b/src/type/check.rs
index 170feec..fd5d1d3 100644
--- a/src/type/check.rs
+++ b/src/type/check.rs
@@ -244,6 +244,13 @@ impl SExp {
                 Ok(arr(List(vec![Integer, Integer]), Boolean)),
             Atom(Or | And | Xor) => Ok(arr(List(vec![Boolean, Boolean]), Boolean)),
             Atom(Not)   => Ok(arr(Boolean, Boolean)),
+	    Atom(Concat) => Ok(arr(
+		List(vec![
+		    List(vec![VecType, vecof(vt("T"))]),
+		    List(vec![VecType, vecof(vt("T"))])
+		]),
+		List(vec![VecType, vecof(vt("T"))])
+	    )),
             Atom(Nil)   => Ok(NilType),
             Atom(Quote) => Ok(arr(
                                vt("T"),
-- 
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