macro: defining macros works

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)
+}