macro: defining macros works

README.md

@@ -9,6 +9,4 @@
 - Destructuring assignment
 - `coerce`
 - `mac`
-- `w/link`
-- `aform`
 - ...

macro/macro.go

@@ -0,0 +1,72 @@
+package macro
+
+import (
+	"fmt"
+
+	"github.com/hellerve/argos/ast"
+)
+
+type Macro struct {
+	params      []string
+	transformer *ast.AST
+}
+
+type MacroEnv map[string]Macro
+
+func NewMacroEnv() MacroEnv {
+	return make(MacroEnv)
+}
+
+func handleMac(l []*ast.AST, m MacroEnv) (*ast.AST, error) {
+	if len(l) != 4 {
+		return nil, fmt.Errorf("mac takes 3 arguments")
+	}
+
+	nameThunk := l[1]
+
+	if nameThunk.Tag != ast.Symbol {
+		return nil, fmt.Errorf("First argument to mac must be symbol, got %s", nameThunk.Pretty())
+	}
+
+	name := nameThunk.Val.(string)
+
+	paramsThunk := l[2]
+
+	if paramsThunk.Tag != ast.List {
+		return nil, fmt.Errorf("second argument to mac must be list, got %s", paramsThunk.Pretty())
+	}
+
+	var params []string
+
+	for _, elem := range paramsThunk.Val.([]*ast.AST) {
+		if elem.Tag != ast.Symbol {
+			return nil, fmt.Errorf("Invalid value in parameter list to mac: %s", elem.Pretty())
+		}
+		params = append(params, elem.Val.(string))
+	}
+
+	m[name] = Macro{params, l[2]}
+
+	nilVal := ast.AST{ast.Symbol, "nil"}
+	return &nilVal, nil
+}
+
+func traverse(l *ast.AST, m MacroEnv) (*ast.AST, error) {
+	vals := l.Val.([]*ast.AST)
+	if len(vals) == 0 {
+		return l, nil
+	}
+
+	if vals[0].Tag == ast.Symbol && vals[0].Val.(string) == "mac" {
+		return handleMac(vals, m)
+	}
+
+	return l, nil
+}
+
+func Expand(l *ast.AST, m MacroEnv) (*ast.AST, error) {
+	if l.Tag != ast.List {
+		return l, nil
+	}
+	return traverse(l, m)
+}

main.go

@@ -10,6 +10,7 @@ import (
 	"github.com/chzyer/readline"
 
 	"github.com/hellerve/argos/eval"
+	"github.com/hellerve/argos/macro"
 	"github.com/hellerve/argos/parser"
 )
 
@@ -23,6 +24,7 @@ func runRepl() {
 	defer rl.Close()
 
 	e := eval.RootEnv()
+	m := macro.NewMacroEnv()
 	for {
 		input, err := rl.Readline()
 
@@ -46,8 +48,15 @@ func runRepl() {
 			continue
 		}
 
+		expanded, err := macro.Expand(parsed, m)
+
+		if err != nil {
+			fmt.Println(err)
+			continue
+		}
+
 		// TODO: how to avoid bindings on error?
-		evald, err := eval.Eval(parsed, e)
+		evald, err := eval.Eval(expanded, e)
 
 		if err != nil {
 			fmt.Println(err)
@@ -60,6 +69,7 @@ func runRepl() {
 
 func runFile(path string) {
 	e := eval.RootEnv()
+	m := macro.NewMacroEnv()
 	input, err := ioutil.ReadFile(path)
 
 	if err != nil {
@@ -79,7 +89,14 @@ func runFile(path string) {
 		return
 	}
 
-	evald, err := eval.Eval(parsed, e)
+	expanded, err := macro.Expand(parsed, m)
+
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+
+	evald, err := eval.Eval(expanded, e)
 
 	if err != nil {
 		fmt.Println(err)