Add Reader options

reader/options.go

@@ -0,0 +1,65 @@
+package reader
+
+import "github.com/spy16/sabre/runtime"
+
+// Option for Reader
+type Option func(*Reader)
+
+// MacroTable is a lookup table that maps the first rune of a macro expression to its
+// implementation.
+type MacroTable map[rune]Macro
+
+// WithMacros sets the macro table for the reader
+func WithMacros(t MacroTable) Option {
+	if t == nil {
+		t = MacroTable{
+			'"':  readString,
+			';':  readComment,
+			':':  readKeyword,
+			'\\': readCharacter,
+			'(':  readList,
+			')':  UnmatchedDelimiter(),
+			'\'': quoteFormReader("quote"),
+			'~':  quoteFormReader("unquote"),
+			'`':  quoteFormReader("syntax-quote"),
+		}
+	}
+
+	return func(r *Reader) {
+		r.macros = t
+	}
+}
+
+// WithDispatch sets the dispatch table for the reader
+func WithDispatch(t MacroTable) Option {
+	if t == nil {
+		t = MacroTable{}
+	}
+
+	return func(r *Reader) {
+		r.dispatch = t
+	}
+}
+
+// WithPredefinedSymbols maps a set of symbols to a set of values globally.
+func WithPredefinedSymbols(ss map[string]runtime.Value) Option {
+	if ss == nil {
+		ss = map[string]runtime.Value{
+			"nil":   runtime.Nil{},
+			"true":  runtime.Bool(true),
+			"false": runtime.Bool(false),
+		}
+	}
+
+	return func(r *Reader) {
+		r.predef = ss
+	}
+}
+
+func withDefaults(opt []Option) []Option {
+	return append([]Option{
+		WithMacros(nil),
+		WithDispatch(nil),
+		WithPredefinedSymbols(nil),
+	}, opt...)
+}

reader/reader.go

@@ -45,12 +45,6 @@ var (
 		'v':  '\v',
 	}
 
-	predefSymbols = map[string]runtime.Value{
-		"nil":   runtime.Nil{},
-		"true":  runtime.Bool(true),
-		"false": runtime.Bool(false),
-	}
-
 	charLiterals = map[string]rune{
 		"tab":       '\t',
 		"space":     ' ',
@@ -65,23 +59,17 @@ var (
 // supports only primitive data  types from runtime  package by default. Support for
 // custom forms can be added using SetMacro(). File name is inferred from the value &
 // type information of 'r' OR can be set manually on the Reader instance returned.
-func New(r io.Reader) *Reader {
-	return &Reader{
+func New(r io.Reader, opts ...Option) *Reader {
+	rd := &Reader{
 		File: inferFileName(r),
 		rs:   bufio.NewReader(r),
-		macros: map[rune]Macro{
-			'"':  readString,
-			';':  readComment,
-			':':  readKeyword,
-			'\\': readCharacter,
-			'(':  readList,
-			')':  UnmatchedDelimiter(),
-			'\'': quoteFormReader("quote"),
-			'~':  quoteFormReader("unquote"),
-			'`':  quoteFormReader("syntax-quote"),
-		},
-		dispatch: map[rune]Macro{},
 	}
+
+	for _, option := range withDefaults(opts) {
+		option(rd)
+	}
+
+	return rd
 }
 
 // Reader consumes characters from a stream and parses them into symbolic expressions
@@ -94,9 +82,10 @@ type Reader struct {
 	buf         []rune
 	line, col   int
 	lastCol     int
-	macros      map[rune]Macro
-	dispatch    map[rune]Macro
+	macros      MacroTable
+	dispatch    MacroTable
 	dispatching bool
+	predef      map[string]runtime.Value
 }
 
 // All consumes characters from stream until EOF and returns a list of all the forms
@@ -364,7 +353,8 @@ func (rd *Reader) readOne() (runtime.Value, error) {
 		return nil, err
 	}
 
-	if predefVal, found := predefSymbols[v.(runtime.Symbol).String()]; found {
+	// TODO(performance):  type assertion necessary given the above call to `readSymbol`?
+	if predefVal, found := rd.predef[v.(runtime.Symbol).String()]; found {
 		return predefVal, nil
 	}
 

repl/options.go

@@ -85,7 +85,9 @@ func WithPrompts(oneLine, multiLine string) Option {
 // Reader. This is useful when you want REPL to use custom reader instance.
 func WithReaderFactory(factory ReaderFactory) Option {
 	if factory == nil {
-		factory = ReaderFactoryFunc(reader.New)
+		factory = ReaderFactoryFunc(func(r io.Reader) *reader.Reader {
+			return reader.New(r)
+		})
 	}
 
 	return func(repl *REPL) {