Implement ++ operator for string concatenation

Author: Rangi42

man/rgbasm.5

@@ -548,7 +548,7 @@ There are a number of escape sequences you can use within a string:
 .El
 .Pp
 Multi-line strings are contained in triple quotes
-.Pq Ql \&"\&"\&"for instance\&"\&"\&" .
+.Pq Ql \&"\&"\&"for instance""" .
 Escape sequences work the same way in multi-line strings; however, literal newline characters will be included as-is, without needing to escape them with
 .Ql \er
 or
@@ -560,10 +560,19 @@ Inside them, backslashes and braces are treated like regular characters, so they
 For example, the raw string
 .Ql #"\et\e1{s}\e"
 is equivalent to the regular string
-.Ql "\e\et\e\e1\e{s}\e\e" .
+.Ql \&"\e\et\e\e1\e{s}\e\e" .
 (Note that this prevents raw strings from including the double quote character.)
 Raw strings also may be contained in triple quotes for them to be multi-line, so they can include literal newline or quote characters (although still not three quotes in a row).
 .Pp
+You can use the
+.Sq ++
+operator to concatenate two strings.
+.Ql \&"str" ++ \&"ing"
+is equivalent to
+.Ql \&"string" ,
+or to
+.Ql STRCAT("str", \&"ing") .
+.Pp
 The following functions operate on string expressions, and return strings themselves.
 .Bl -column "STRSLICE(str, start, stop)"
 .It Sy Name Ta Sy Operation

src/asm/lexer.cpp

@@ -1774,12 +1774,17 @@ static Token yylex_NORMAL() {
 
 			// Handle ambiguous 1- or 2-char tokens
 
-		case '+': // Either += or ADD
-			if (peek() == '=') {
+		case '+': // Either +=, ADD, or CAT
+			switch (peek()) {
+			case '=':
 				shiftChar();
 				return Token(T_(POP_ADDEQ));
+			case '+':
+				shiftChar();
+				return Token(T_(OP_CAT));
+			default:
+				return Token(T_(OP_ADD));
 			}
-			return Token(T_(OP_ADD));
 
 		case '-': // Either -= or SUB
 			if (peek() == '=') {

src/asm/parser.y

@@ -125,6 +125,9 @@
 %token OP_MUL "*" OP_DIV "/" OP_MOD "%"
 %token OP_EXP "**"
 
+// String operators
+%token OP_CAT "++"
+
 // Comparison operators
 %token OP_LOGICEQU "==" OP_LOGICNE "!="
 %token OP_LOGICLT "<" OP_LOGICGT ">"
@@ -147,6 +150,7 @@
 %left OP_AND OP_OR OP_XOR
 %left OP_SHL OP_SHR OP_USHR
 %left OP_MUL OP_DIV OP_MOD
+%left OP_CAT
 %precedence NEG // applies to unary OP_LOGICNOT, OP_ADD, OP_SUB, OP_NOT
 %right OP_EXP
 
@@ -1613,6 +1617,10 @@ string_literal:
 	STRING {
 		$$ = std::move($1);
 	}
+	| string OP_CAT string {
+		$$ = std::move($1);
+		$$.append($3);
+	}
 	| OP_STRSLICE LPAREN string COMMA iconst COMMA iconst RPAREN {
 		size_t len = strlenUTF8($3, false);
 		uint32_t start = adjustNegativeIndex($5, len, "STRSLICE");

test/asm/string-concat.asm

@@ -0,0 +1,26 @@
+SECTION "test", ROM0
+
+MACRO test
+	assert !strcmp(\1, \2)
+ENDM
+
+test "a"++"b", "ab"
+test "a"++""++"b", "ab"
+test "a"++"b", strcat("a", "b")
+test "a"++"b"++"c", strcat("a","b","c")
+test "" ++ "", ""
+test strupr("a") ++ strlwr("B"), "Ab"
+
+def str equs "hi"
+test #str ++ strupr(#str), "hiHI"
+test "a" ++ """b""" ++ strupr("c") ++ strslice(#str, 0, 0), "abC"
+
+charmap "a", 1
+charmap "b", 2
+charmap "ab", 12
+assert "a" + "b" == 3
+assert "a" ++ "b" == 12
+
+; errors
+assert 2 ++ 2 == 4
+ld a, [hl++]

test/asm/string-concat.err

@@ -0,0 +1,5 @@
+error: string-concat.asm(25):
+    syntax error, unexpected ++
+error: string-concat.asm(26):
+    syntax error, unexpected ++, expecting ] or + or -
+error: Assembly aborted (2 errors)!