From 49e1bf204f66ec584e921acca1c6a0ee2890d259 Mon Sep 17 00:00:00 2001
From: "Johan B.W. de Vries" <info@jbwdevries.nl>
Date: Sun, 25 Jan 2026 13:14:21 +0100
Subject: [PATCH] Adds backslash as a build in constant

---
 0-lang0py/lang0py.py                                  | 2 ++
 1-lang0py/lang0py.lang0                               | 2 ++
 2-lang0c/lang0c.lang0                                 | 2 ++
 README.md                                             | 4 ++++
 tests/test_stdlib_constants/test_backslash.exp.stdout | 1 +
 tests/test_stdlib_constants/test_backslash.lang0      | 3 +++
 6 files changed, 14 insertions(+)
 create mode 100644 tests/test_stdlib_constants/test_backslash.exp.stdout
 create mode 100644 tests/test_stdlib_constants/test_backslash.lang0

diff --git a/0-lang0py/lang0py.py b/0-lang0py/lang0py.py
index 97cb13b..e148d3d 100644
--- a/0-lang0py/lang0py.py
+++ b/0-lang0py/lang0py.py
@@ -409,6 +409,7 @@ def emitheader():
     emitln("    if os.environ.get('TRACE'):")
     emitln("        sys.stderr.write(f'{header}={value!r}\\n')")
     emitln("")
+    emitln("__BACKSLASH = chr(0x5C)")
     emitln("__EOF = chr(0xFF)")
     emitln("__EOL = chr(10)")
     emitln("__QUOTE = chr(34)")
@@ -495,6 +496,7 @@ def main():
     emitheader()
 
     # Standard library constants
+    mapsetkey("REGISTERID", "backslash", "__BACKSLASH")
     mapsetkey("REGISTERID", "eof", "__EOF")
     mapsetkey("REGISTERID", "eol", "__EOL")
     mapsetkey("REGISTERID", "quote", "__QUOTE")
diff --git a/1-lang0py/lang0py.lang0 b/1-lang0py/lang0py.lang0
index 3435074..ba57c7a 100644
--- a/1-lang0py/lang0py.lang0
+++ b/1-lang0py/lang0py.lang0
@@ -472,6 +472,7 @@ emitheader:
 	emitln "    if os.environ.get('TRACE'):"
 	emitln "        sys.stderr.write(f'{header}={value!r}\\n')"
 	emitln ""
+	emitln "__BACKSLASH = chr(0x5C)"
 	emitln "__EOF = chr(0xFF)"
 	emitln "__EOL = chr(10)"
 	emitln "__QUOTE = chr(34)"
@@ -557,6 +558,7 @@ emitfooter:
 main:
 	emitheader
 
+	mapsetkey "REGISTERID" "backslash" "__BACKSLASH"
 	mapsetkey "REGISTERID" "eof" "__EOF"
 	mapsetkey "REGISTERID" "eol" "__EOL"
 	mapsetkey "REGISTERID" "quote" "__QUOTE"
diff --git a/2-lang0c/lang0c.lang0 b/2-lang0c/lang0c.lang0
index 39082bb..7f42938 100644
--- a/2-lang0c/lang0c.lang0
+++ b/2-lang0c/lang0c.lang0
@@ -574,6 +574,7 @@ emitheader:
 	emitln "#include <string.h>"
 	emitln ""
 	emitln ""
+	emitln "char __BACKSLASH[2] = {0x5C, 0};"
 	emitln "char __EOF[2] = {0xFF, 0};"
 	emitln "char __EOL[2] = {10, 0};"
 	emitln "char __QUOTE[2] = {34, 0};"
@@ -849,6 +850,7 @@ main:
 
 	emitheader
 
+	mapsetkey "REGISTERID" "backslash" "__BACKSLASH"
 	mapsetkey "REGISTERID" "eof" "__EOF"
 	mapsetkey "REGISTERID" "eol" "__EOL"
 	mapsetkey "REGISTERID" "quote" "__QUOTE"
diff --git a/README.md b/README.md
index 5098cf5..ad809bc 100644
--- a/README.md
+++ b/README.md
@@ -123,6 +123,10 @@ Writes the name and value of the variable passed to stderr if the TRACE environm
 
 ### Standard library constants
 
+#### backslash
+
+Backslash character.
+
 #### eof
 
 End of file character, zero byte.
diff --git a/tests/test_stdlib_constants/test_backslash.exp.stdout b/tests/test_stdlib_constants/test_backslash.exp.stdout
new file mode 100644
index 0000000..b7d5379
--- /dev/null
+++ b/tests/test_stdlib_constants/test_backslash.exp.stdout
@@ -0,0 +1 @@
+\
\ No newline at end of file
diff --git a/tests/test_stdlib_constants/test_backslash.lang0 b/tests/test_stdlib_constants/test_backslash.lang0
new file mode 100644
index 0000000..19c2d50
--- /dev/null
+++ b/tests/test_stdlib_constants/test_backslash.lang0
@@ -0,0 +1,3 @@
+main:
+	emit backslash
+/