simple while

ast_string.go

@@ -117,3 +117,11 @@ func (as *AstStringer) visitIfStmt(i *IfStmt) {
 func (as *AstStringer) visitEnvStmt(e *EnvStmt) {
 	as.str.WriteString("(env)")
 }
+
+func (as *AstStringer) visitWhileStmt(w *WhileStmt) {
+	as.str.WriteString("(while ")
+	w.cond.accept(as)
+	as.str.WriteString(" ")
+	w.body.accept(as)
+	as.str.WriteString(")")
+}

env.go

@@ -33,5 +33,10 @@ func (env *Environment) exists(key string) bool {
 }
 
 func (env *Environment) set(key string, val any) {
+
+	if env.parent != nil && env.parent.exists(key) {
+		env.parent.set(key, val)
+	}
+
 	env.values[key] = val
 }

interpreter.go

@@ -210,7 +210,12 @@ func (i *Interpreter) visitEnvStmt(e *EnvStmt) {
 		fmt.Printf("%*s", ident, "")
 		fmt.Printf("%+v\n", *e)
 	}
+}
 
+func (i *Interpreter) visitWhileStmt(w *WhileStmt) {
+	for isTruthy(i.evaluate(w.cond)) {
+		w.body.accept(i)
+	}
 }
 
 func (i *Interpreter) panic(re *RuntimeError) {

parser.go

@@ -66,14 +66,20 @@ func (p *Parser) varDecl() Stmt {
 	return &VarStmt{name, initializer}
 }
 
-// statement -> exprStmt | printStmt | block | ifStmt | env
+// statement ->  exprStmt
+//
+//	| whileStmt
+//	| printStmt
+//	| blockStmt
+//	| ifStmt
+//	| env
 func (p *Parser) statement() Stmt {
 	if p.match(PRINT) {
 		return p.printStmt()
 	}
 
 	if p.match(LEFT_BRACE) {
-		return p.block()
+		return p.blockStmt()
 	}
 
 	if p.match(IF) {
@@ -84,6 +90,10 @@ func (p *Parser) statement() Stmt {
 		return p.envStmt()
 	}
 
+	if p.match(WHILE) {
+		return p.whileStmt()
+	}
+
 	return p.exprStmt()
 }
 
@@ -111,8 +121,8 @@ func (p *Parser) printStmt() Stmt {
 	return &PrintStmt{expr}
 }
 
-// block -> "{" statement* "}"
-func (p *Parser) block() Stmt {
+// blockStmt -> "{" statement* "}"
+func (p *Parser) blockStmt() Stmt {
 
 	stmts := []Stmt{}
 	for !p.check(RIGHT_BRACE) && !p.isAtEnd() {
@@ -140,6 +150,16 @@ func (p *Parser) ifStmt() Stmt {
 	return &IfStmt{name, expr, then, or}
 }
 
+// while -> "while" "(" expression ")" statement
+func (p *Parser) whileStmt() Stmt {
+	p.consume(LEFT_PAREN, "Expect '(' after 'while'.")
+	cond := p.expression()
+	p.consume(RIGHT_PAREN, "Expect ')' after 'while' expression.")
+	body := p.statement()
+
+	return &WhileStmt{cond, body}
+}
+
 // env -> "env" ";"
 func (p *Parser) envStmt() Stmt {
 	p.consume(SEMICOLON, "Expect ';' after 'env'.")

stmt.go

@@ -7,6 +7,7 @@ type StmtVisitor interface {
 	visitPrintStmt(p *PrintStmt)
 	visitBlockStmt(b *BlockStmt)
 	visitEnvStmt(e *EnvStmt)
+	visitWhileStmt(w *WhileStmt)
 }
 
 type Stmt interface {
@@ -40,12 +41,18 @@ type IfStmt struct {
 	or   Stmt
 }
 
+type WhileStmt struct {
+	cond Expr
+	body Stmt
+}
+
 func (i *IfStmt) stmt()    {}
+func (e *EnvStmt) stmt()   {}
 func (vs *VarStmt) stmt()  {}
 func (es *ExprStmt) stmt() {}
 func (p *PrintStmt) stmt() {}
 func (b *BlockStmt) stmt() {}
-func (e *EnvStmt) stmt()   {}
+func (w *WhileStmt) stmt() {}
 
 func (p *PrintStmt) accept(v StmtVisitor) {
 	v.visitPrintStmt(p)
@@ -70,3 +77,7 @@ func (i *IfStmt) accept(v StmtVisitor) {
 func (e *EnvStmt) accept(v StmtVisitor) {
 	v.visitEnvStmt(e)
 }
+
+func (w *WhileStmt) accept(v StmtVisitor) {
+	v.visitWhileStmt(w)
+}