Allow I/O operations to have a level of indirection.

builtins/builtins.go

@@ -1454,13 +1454,18 @@ func printFn(env *env.Environment, args []primitive.Primitive) primitive.Primiti
 		return primitive.ArityError()
 	}
 
+	ioHelper := env.GetIOConfig()
+
 	// one arg
 	if len(args) == 1 {
 		// expand
 		str := expandStr(args[0].ToString())
 
-		// show & return
-		fmt.Println(str)
+		// Write via our configuration object
+		// Linter complains about ignored return values here..
+		_, _ = ioHelper.STDOUT.Write([]byte(str))
+		_, _ = ioHelper.STDOUT.Write([]byte("\n"))
+
 		return primitive.String(str)
 	}
 
@@ -1481,7 +1486,12 @@ func printFn(env *env.Environment, args []primitive.Primitive) primitive.Primiti
 	}
 
 	out := fmt.Sprintf(frmt, parm...)
-	fmt.Println(out)
+
+	// Write via our configuration object
+	// Linter complains about ignored return values here..
+	_, _ = ioHelper.STDOUT.Write([]byte(out))
+	_, _ = ioHelper.STDOUT.Write([]byte("\n"))
+
 	return primitive.String(out)
 }
 

builtins/builtins_test.go

@@ -1,6 +1,7 @@
 package builtins
 
 import (
+	"bytes"
 	"math"
 	"os"
 	"path/filepath"
@@ -9,6 +10,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/skx/yal/config"
 	"github.com/skx/yal/env"
 	"github.com/skx/yal/eval"
 	"github.com/skx/yal/primitive"
@@ -21,6 +23,10 @@ var ENV *env.Environment
 // init ensures our environment pointer is up to date.
 func init() {
 	ENV = env.New()
+
+	// Environment will have a config
+	ENV.SetIOConfig(config.DefaultIO())
+
 }
 
 func TestArch(t *testing.T) {
@@ -3046,6 +3052,31 @@ func TestPrint(t *testing.T) {
 		t.Fatalf("got string, but wrong one %v", e2)
 	}
 
+	// Preserve the current config
+	orig := ENV.GetIOConfig()
+
+	// Setup a new STDOUT handle, pointing to a buffer
+	cfg := config.New()
+	tmp := new(bytes.Buffer)
+	cfg.STDOUT = tmp
+	ENV.SetIOConfig(cfg)
+
+	// Print something
+	printFn(ENV, []primitive.Primitive{
+		primitive.String("Hello %s!"),
+		primitive.List{
+			primitive.String("world"),
+			primitive.Number(42),
+		},
+	})
+
+	// Restore our handles
+	ENV.SetIOConfig(orig)
+
+	// Our buffer should be good
+	if tmp.String() != "Hello (world 42)!\n" {
+		t.Fatalf("(print 'hello (list)!') failed, got '%s'", tmp.String())
+	}
 }
 
 // TestRandom tests (random)
@@ -3524,7 +3555,7 @@ func TestStringLt(t *testing.T) {
 	}
 }
 
-func TestTrig(t *testing.T ) {
+func TestTrig(t *testing.T) {
 
 	funs := []primitive.GolangPrimitiveFn{
 		acosFn,
@@ -3538,9 +3569,9 @@ func TestTrig(t *testing.T ) {
 		tanhFn,
 	}
 
-	for _, fn := range(funs) {
+	for _, fn := range funs {
 
-		out := fn(nil, []primitive.Primitive{} )
+		out := fn(nil, []primitive.Primitive{})
 
 		// Will lead to an error
 		e, ok := out.(primitive.Error)

builtins/file_info_unix.go

@@ -18,7 +18,6 @@ func getGID(info os.FileInfo) (int, error) {
 	return int(stat.Gid), nil
 }
 
-
 // getUID returns the owner of the file, from the extended information
 // available after a stat - that is not portable to Windows though.
 //

config/config.go

@@ -0,0 +1,47 @@
+// Package config provides an I/O abstraction for our interpreter,
+// allowing it to be embedded and used in places where STDIN and STDOUT
+// are not necessarily terminal-based.
+//
+// All input-reading uses the level of indirection provided here, and
+// similarly output goes via the writer we hold here.
+//
+// This abstraction allows a host program to setup a different pair of
+// streams prior to initializing the interpreter.
+package config
+
+import (
+	"io"
+	"os"
+)
+
+// Config is a holder for configuration which is used for interfacing
+// the interpreter with the outside world.
+type Config struct {
+
+	// STDIN is an input-reader used for the (read) function, when
+	// called with no arguments.
+	STDIN io.Reader
+
+	// STDOUT is the writer which is used for "(print)".
+	STDOUT io.Writer
+}
+
+// New returns a new configuration object
+func New() *Config {
+
+	e := &Config{}
+	return e
+}
+
+// DefaultIO returns a configuration which uses the default
+// input and output streams - i.e. STDIN and STDOUT work as
+// expected
+func DefaultIO() *Config {
+	e := New()
+
+	// Setup default input/output streams
+	e.STDIN = os.Stdin
+	e.STDOUT = os.Stdout
+
+	return e
+}

env/env.go

@@ -9,6 +9,10 @@
 // or call-frames, you can create a nested environment via NewEnvironment.
 package env
 
+import (
+	"github.com/skx/yal/config"
+)
+
 // Environment holds our state
 type Environment struct {
 
@@ -17,6 +21,10 @@ type Environment struct {
 
 	// values holds the actual values
 	values map[string]any
+
+	// ioconfig holds the interface to the outside world,
+	// which is used for I/O
+	ioconfig *config.Config
 }
 
 // Get retrieves a value from the environment.
@@ -59,16 +67,18 @@ func (env *Environment) Items() map[string]any {
 // New creates a new environment, with no parent.
 func New() *Environment {
 	return &Environment{
-		values: map[string]any{},
+		values:   map[string]any{},
+		ioconfig: config.New(),
 	}
 }
 
 // NewEnvironment creates a new environment, which will use the specified
 // parent environment for values in a higher level.
 func NewEnvironment(parent *Environment) *Environment {
 	return &Environment{
-		parent: parent,
-		values: map[string]any{},
+		parent:   parent,
+		values:   map[string]any{},
+		ioconfig: parent.ioconfig,
 	}
 }
 
@@ -87,3 +97,15 @@ func (env *Environment) SetOuter(key string, value any) {
 		env.parent.SetOuter(key, value)
 	}
 }
+
+// SetIOConfig updates the configuration object which is stored
+// in our environment
+func (env *Environment) SetIOConfig(cfg *config.Config) {
+	env.ioconfig = cfg
+}
+
+// GetIOConfig returns the configuration object which is stored in
+// our environment.
+func (env *Environment) GetIOConfig() *config.Config {
+	return env.ioconfig
+}

eval/eval.go

@@ -6,12 +6,10 @@
 package eval
 
 import (
-	"bufio"
 	"context"
 	"errors"
 	"flag"
 	"fmt"
-	"os"
 	"regexp"
 	"strconv"
 	"strings"
@@ -59,14 +57,6 @@ type Eval struct {
 	// The key is the name of the fake method, the value the name of
 	// the field to get/set
 	accessors map[string]string
-
-	// STDIN is an input-reader used for the (read) function, when
-	// called with no arguments.
-	STDIN *bufio.Reader
-
-	// STDOUT is the writer which we should use for "(print)", but we
-	// currently don't.
-	STDOUT *bufio.Writer
 }
 
 // New constructs a new lisp interpreter.
@@ -93,10 +83,6 @@ func New(src string) *Eval {
 		accessors: make(map[string]string),
 	}
 
-	// Setup default input/output streams
-	e.STDIN = bufio.NewReader(os.Stdin)
-	e.STDOUT = bufio.NewWriter(os.Stdout)
-
 	// Setup the default symbol-table (interned) entries.
 
 	// true

eval/eval_test.go

@@ -8,6 +8,7 @@ import (
 	"time"
 
 	"github.com/skx/yal/builtins"
+	"github.com/skx/yal/config"
 	"github.com/skx/yal/env"
 	"github.com/skx/yal/primitive"
 	"github.com/skx/yal/stdlib"
@@ -26,6 +27,9 @@ func TestAliased(t *testing.T) {
 	// With a new environment
 	env := env.New()
 
+	// Environment will have a config
+	env.SetIOConfig(config.DefaultIO())
+
 	// Populate the default primitives
 	builtins.PopulateEnvironment(env)
 
@@ -416,6 +420,9 @@ a
 			// With a new environment
 			env := env.New()
 
+			// Environment will have a config
+			env.SetIOConfig(config.DefaultIO())
+
 			// Populate the default primitives
 			builtins.PopulateEnvironment(env)
 

eval/specials.go

@@ -3,6 +3,7 @@
 package eval
 
 import (
+	"bufio"
 	"fmt"
 	"strings"
 
@@ -286,7 +287,10 @@ func (ev *Eval) evalSpecialForm(name string, args []primitive.Primitive, e *env.
 
 		// zero arguments: read from STDIN
 		if len(args) == 0 {
-			input, err := ev.STDIN.ReadString('\n')
+
+			ioHelper := e.GetIOConfig()
+			r := bufio.NewReader(ioHelper.STDIN)
+			input, err := r.ReadString('\n')
 			if err != nil {
 				return primitive.Error(
 					fmt.Sprintf("failed to read from STDIN %s", err)), true

fuzz_test.go

@@ -12,6 +12,7 @@ import (
 	"time"
 
 	"github.com/skx/yal/builtins"
+	"github.com/skx/yal/config"
 	"github.com/skx/yal/env"
 	"github.com/skx/yal/eval"
 	"github.com/skx/yal/primitive"
@@ -188,6 +189,9 @@ func FuzzYAL(f *testing.F) {
 		// Create a new environment
 		environment := env.New()
 
+		// Environment will have a config
+		environment.SetIOConfig(config.DefaultIO())
+
 		// Populate the default primitives
 		builtins.PopulateEnvironment(environment)
 

main.go

@@ -18,6 +18,7 @@ import (
 	"time"
 
 	"github.com/skx/yal/builtins"
+	"github.com/skx/yal/config"
 	"github.com/skx/yal/env"
 	"github.com/skx/yal/eval"
 	"github.com/skx/yal/primitive"
@@ -43,6 +44,9 @@ func create() {
 	// Create a new environment
 	ENV = env.New()
 
+	// Setup the I/O
+	ENV.SetIOConfig(config.DefaultIO())
+
 	// Populate the default primitives
 	builtins.PopulateEnvironment(ENV)