feat(codegen): convert implicitly between CHAR and STRING

A CHAR becomes a one-character STRING in &, comparisons, assignment,
parameter passing and RETURN. A STRING becomes a CHAR in assignment,
parameter passing and RETURN, with a runtime error when its length is
not 1. CHAR with INTEGER or BOOLEAN still does not convert.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

2 files changed, 2 insertions, 2 deletions

diff --git a/doc/language/cpsc-language-overview.7.md b/doc/language/cpsc-language-overview.7.md
index b1376d8..914126e 100644
--- a/doc/language/cpsc-language-overview.7.md
+++ b/doc/language/cpsc-language-overview.7.md
@@ -10,7 +10,7 @@ Keywords are uppercase and case-sensitive. Identifiers, including built-in funct
 
 Assign with ASCII `<-`: `Count <- Count + 1`. Compare with `=`, `<>`, `<`, `>`, `<=`, and `>=`. Standard-library STRING comparisons compare contents, case-sensitively. Use `+`, `-`, `*`, and `/` for arithmetic; built-in `/` always returns REAL. Use `&` to join strings.
 
-User-defined types can overload operators with OVERLOAD FUNCTION OPERATOR; expressions then use the declared result type. See [cpsc-keyword-operator(7)](keyword/cpsc-keyword-operator.7.md). STRING cannot be implicitly converted to BOOLEAN. Typing is strict: arithmetic and unary minus accept only INTEGER and REAL, a comparison needs operands of the same type (or INTEGER with REAL), and BOOLEAN, CHAR and INTEGER never convert into one another implicitly (only INTEGER converts to REAL). Use ASC and CHR to move between CHAR and INTEGER. REAL never converts to INTEGER implicitly; use INT.
+User-defined types can overload operators with OVERLOAD FUNCTION OPERATOR; expressions then use the declared result type. See [cpsc-keyword-operator(7)](keyword/cpsc-keyword-operator.7.md). STRING cannot be implicitly converted to BOOLEAN. Typing is strict: arithmetic and unary minus accept only INTEGER and REAL, a comparison needs operands of the same type (or INTEGER with REAL), and BOOLEAN, CHAR and INTEGER never convert into one another implicitly (only INTEGER converts to REAL). Use ASC and CHR to move between CHAR and INTEGER. CHAR and STRING do convert implicitly: a CHAR becomes a one-character STRING in `&`, in comparisons, in assignment, in argument passing and in RETURN, and a STRING becomes a CHAR in assignment, argument passing and RETURN (for example `c <- MID(s, i, 1)`); a STRING whose length is not 1 is a runtime error that TRY/CATCH can catch. REAL never converts to INTEGER implicitly; use INT.
 
 Precedence, from highest to lowest: unary operators, `* / DIV MOD`, `+ - &`, comparisons, AND, OR. Parentheses override precedence.
 
diff --git a/doc/language/function/cpsc-function-chr.7.md b/doc/language/function/cpsc-function-chr.7.md
index cc471a5..3ae8612 100644
--- a/doc/language/function/cpsc-function-chr.7.md
+++ b/doc/language/function/cpsc-function-chr.7.md
@@ -14,7 +14,7 @@ CHR(code : INTEGER) RETURNS STRING
 
 Provided by the standard string library, loaded and linked by default.
 
-Convert the low eight bits of code to a one-byte string. The result is STRING, not CHAR. Use ASCII codes 1 to 127 for ordinary text; code 0 produces one NUL byte, so LENGTH(CHR(0)) is 1.
+Convert the low eight bits of code to a one-byte string. The result is STRING, not CHAR, but a STRING of length 1 converts implicitly to CHAR on assignment. Use ASCII codes 1 to 127 for ordinary text; code 0 produces one NUL byte, so LENGTH(CHR(0)) is 1.
 
 # EXAMPLE