add REPL command :unload PACKAGE-PATH. fixes #15

base/global.go

@@ -34,6 +34,7 @@ import (
 	r "reflect"
 	"strings"
 
+	"github.com/cosmos72/gomacro/imports"
 	mp "github.com/cosmos72/gomacro/parser"
 	mt "github.com/cosmos72/gomacro/token"
 
@@ -140,6 +141,27 @@ func (g *Globals) ParseBytes(src []byte) []ast.Node {
 	return nodes
 }
 
+func (g *Globals) UnloadImport(path string) {
+	if n := len(path); n > 1 && path[0] == '"' && path[n-1] == '"' {
+		path = path[1 : n-1] // remove quotes
+	}
+	slash := strings.IndexByte(path, '/')
+	if _, found := imports.Packages[path]; !found {
+		if slash < 0 {
+			g.Debugf("nothing to unload: cannot find imported package %q. Remember to specify the full package path, not only its name", path)
+		} else {
+			g.Debugf("nothing to unload: cannot find imported package %q", path)
+		}
+	}
+	delete(imports.Packages, path)
+	dot := strings.IndexByte(path, '.')
+	if slash < 0 || dot > slash {
+		g.Warnf("unloaded standard library package %q. attempts to import it again may trigger a reload", path)
+		return
+	}
+	g.Debugf("unloaded package %q. attempts to import it again may trigger a reload", path)
+}
+
 // CollectAst accumulates declarations in ir.Decls and statements in ir.Stmts
 // allows generating a *.go file on user request
 func (g *Globals) CollectAst(form Ast) {

classic/interpreter.go

@@ -211,6 +211,11 @@ func (ir *Interp) parseEvalPrint(src string, in Readline) (callAgain bool) {
 			return true
 		case strings.HasPrefix(":quit", cmd):
 			return false
+		case strings.HasPrefix(":unload", cmd):
+			if len(args) > 1 {
+				g.UnloadImport(args[1])
+			}
+			return true
 		case strings.HasPrefix(":write", cmd):
 			if len(args) <= 1 {
 				env.WriteDeclsToStream(env.Stdout)

classic/output.go

@@ -45,13 +45,14 @@ func (ir *ThreadGlobals) ShowHelp(out io.Writer) {
 	fmt.Fprint(out, `// type Go code to execute it. example: func add(x, y int) int { return x + y }
 
 // interpreter commands:
-:classic CODE   execute CODE using the classic interpreter
+:classic [CODE]  execute CODE using the classic interpreter
 :env [name]     show available functions, variables and constants
                 in current package, or from imported package "name"
-:fast CODE      execute CODE using the fast interpreter (default)
+:fast [CODE]    execute CODE using the fast interpreter (default)
 :help           show this help
 :inspect EXPR   inspect expression interactively
 :options [OPTS] show or toggle interpreter options
+:unload PACKAGE unload PACKAGE. Later attempts to import it may still reload it.
 :quit           quit the interpreter
 :write [FILE]   write collected declarations and/or statements to standard output or to FILE
                 use :o Declarations and/or :o Statements to start collecting them