cgen/ast/checker: string interpolation

vlib/strings/builder_c.v

@@ -55,6 +55,26 @@ pub fn (b mut Builder) writeln(s string) {
 	b.len += s.len + 1
 }
 
+// buf == 'hello world'
+// last_n(5) returns 'world'
+pub fn (b mut Builder) last_n(n int) string {
+	if n > b.len {
+		return ''
+	}
+	buf := b.buf[b.len-n..]
+	return string(buf.clone())
+}
+
+// buf == 'hello world'
+// after(6) returns 'world'
+pub fn (b mut Builder) after(n int) string {
+	if n >= b.len {
+		return ''
+	}
+	buf := b.buf[n..]
+	return string(buf.clone())
+}
+
 pub fn (b mut Builder) str() string {
 	b.buf << `\0`
 	return string(b.buf,b.len)

vlib/v/ast/ast.v

@@ -14,7 +14,7 @@ pub type Expr = InfixExpr | IfExpr | StringLiteral | IntegerLiteral | CharLitera
 FloatLiteral | Ident | CallExpr | BoolLiteral | StructInit | ArrayInit | SelectorExpr | PostfixExpr | 	
 AssignExpr | PrefixExpr | MethodCallExpr | IndexExpr | RangeExpr | MatchExpr | 	
 CastExpr | EnumVal | Assoc | SizeOf | None | MapInit | IfGuardExpr | ParExpr | OrExpr | 	
-ConcatExpr | Type | AsCast | TypeOf
+ConcatExpr | Type | AsCast | TypeOf | StringInterLiteral
 
 pub type Stmt = GlobalDecl | FnDecl | Return | Module | Import | ExprStmt | 	
 ForStmt | StructDecl | ForCStmt | ForInStmt | CompIf | ConstDecl | Attr | BranchStmt | 	
@@ -54,6 +54,15 @@ pub:
 	val string
 }
 
+// 'name: $name'
+pub struct StringInterLiteral {
+pub:
+	vals       []string
+	exprs      []Expr
+mut:
+	expr_types []table.Type
+}
+
 pub struct CharLiteral {
 pub:
 	val string

vlib/v/checker/checker.v

@@ -393,7 +393,8 @@ pub fn (c mut Checker) return_stmt(return_stmt mut ast.Return) {
 		return
 	}
 	if expected_types.len > 0 && expected_types.len != got_types.len {
-		c.error('wrong number of return arguments:\n\texpected: $expected_types.str()\n\tgot: $got_types.str()', return_stmt.pos)
+		// c.error('wrong number of return arguments:\n\texpected: $expected_types.str()\n\tgot: $got_types.str()', return_stmt.pos)
+		c.error('wrong number of return arguments', return_stmt.pos)
 	}
 	for i, exp_typ in expected_types {
 		got_typ := got_types[i]
@@ -737,6 +738,12 @@ pub fn (c mut Checker) expr(node ast.Expr) table.Type {
 		ast.StringLiteral {
 			return table.string_type
 		}
+		ast.StringInterLiteral {
+			for expr in it.exprs {
+				it.expr_types << c.expr(expr)
+			}
+			return table.string_type
+		}
 		ast.StructInit {
 			return c.struct_init(mut it)
 		}

vlib/v/gen/cgen.v

@@ -868,6 +868,9 @@ fn (g mut Gen) expr(node ast.Expr) {
 				g.write('tos3("$escaped_val")')
 			}
 		}
+		ast.StringInterLiteral {
+			g.string_inter_literal(it)
+		}
 		// `user := User{name: 'Bob'}`
 		ast.StructInit {
 			styp := g.typ(it.typ)
@@ -1652,6 +1655,46 @@ fn (g &Gen) sort_structs(types []table.TypeSymbol) []table.TypeSymbol {
 	return types_sorted
 }
 
+fn (g mut Gen) string_inter_literal(node ast.StringInterLiteral) {
+	g.write('_STR("')
+	// Build the string with %
+	for i, val in node.vals {
+		g.write(val)
+		if i >= node.exprs.len {
+			continue
+		}
+		pos := g.out.len
+		match node.expr_types[i] {
+			table.string_type {
+				g.write('%.*s')
+			}
+			table.int_type {
+				g.write('%d')
+			}
+			else {}
+	}
+	}
+	g.write('", ')
+	// Build args
+	for i, expr in node.exprs {
+		if node.expr_types[i] == table.string_type {
+			// `name.str, name.len,`
+			g.expr(node.exprs[i])
+			g.write('.len, ')
+			g.expr(node.exprs[i])
+			g.write('.str')
+		}
+		else {
+			g.expr(node.exprs[i])
+		}
+		if i < node.exprs.len - 1 {
+			g.write(', ')
+		}
+	}
+	g.write(')')
+}
+
+// `nums.filter(it % 2 == 0)`
 fn (g mut Gen) gen_filter(node ast.MethodCallExpr) {
 	tmp := g.new_tmp_var()
 	buf := g.out.buf[g.stmt_start_pos..]

vlib/v/gen/tests/3.c

@@ -37,6 +37,11 @@ tos3(""),
 	if (a == 10 || a == 20 || a == 30) {
 		int b = 10;
 	}
+	string name = tos3("Bob");
+	println(tos3("hello"));
+	println(_STR("Hello, %.*s", name.len, name.str));
+	println(_STR("age = %d", age));
+	println(_STR("name=%.*s age=%d", name.len, name.str, age));
 }
 
 void println(string s) {

vlib/v/gen/tests/3.vv

@@ -30,6 +30,11 @@ fn (u &User) foo() {
 	if a in [10, 20, 30] {
 		b := 10
 	}
+	name := 'Bob'
+	println('hello')
+	println('Hello, $name')
+	println('age = $age')
+	println('name=$name age=$age')
 }
 
 fn println(s string) {}

vlib/v/parser/parser.v

@@ -1243,21 +1243,25 @@ fn (p mut Parser) if_expr() ast.IfExpr {
 
 fn (p mut Parser) string_expr() ast.Expr {
 	mut node := ast.Expr{}
+	val := p.tok.lit
 	node = ast.StringLiteral{
-		val: p.tok.lit
+		val: val
 	}
 	if p.peek_tok.kind != .str_dollar {
 		p.next()
 		return node
 	}
+	mut exprs := []ast.Expr
+	mut vals := []string
 	// Handle $ interpolation
 	for p.tok.kind == .string {
+		vals << p.tok.lit
 		p.next()
 		if p.tok.kind != .str_dollar {
 			continue
 		}
 		p.check(.str_dollar)
-		p.expr(0)
+		exprs << p.expr(0)
 		if p.tok.kind == .colon {
 			p.next()
 		}
@@ -1273,6 +1277,10 @@ fn (p mut Parser) string_expr() ast.Expr {
 			}
 		}
 	}
+	node = ast.StringInterLiteral{
+		vals: vals
+		exprs: exprs
+	}
 	return node
 }