Go: move the stdlib to a different file

2 files changed, 513 insertions, 495 deletions

diff --git a/ell/ell.go b/ell/ell.go
index af4c407..7995a86 100644
--- a/ell/ell.go
+++ b/ell/ell.go
@@ -20,11 +20,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-
-	// standard library
-	"bytes"
-	"os"
-	"os/exec"
 )
 
 // --- Values ------------------------------------------------------------------
@@ -717,493 +712,3 @@ func (ell *Ell) EvalBlock(body []V, args []V) (result []V, ok bool) {
 	ell.scopes = ell.scopes[:len(ell.scopes)-1]
 	return result, ok
 }
-
-// --- Standard library --------------------------------------------------------
-
-// EvalAny evaluates any value and appends to the result.
-func EvalAny(ell *Ell, body *V, arg *V) (result []V, ok bool) {
-	if body.Type == VTypeString {
-		return []V{*body}, true
-	}
-	var args []V
-	if arg != nil {
-		args = append(args, *arg.Clone())
-	}
-	if res, ok := ell.EvalBlock(body.List, args); ok {
-		return res, true
-	}
-	return nil, false
-}
-
-// NewNumber creates a new string value containing a number.
-func NewNumber(n float64) *V {
-	s := fmt.Sprintf("%f", n)
-	i := len(s)
-	for i > 0 && s[i-1] == '0' {
-		i--
-	}
-	if s[i-1] == '.' {
-		i--
-	}
-	return NewString(s[:i])
-}
-
-// Truthy decides whether any value is logically true.
-func Truthy(v *V) bool {
-	return v != nil && (len(v.List) > 0 || len(v.String) > 0)
-}
-
-// NewBoolean creates a new string value copying the boolean's truthiness.
-func NewBoolean(b bool) *V {
-	if b {
-		return NewString("1")
-	}
-	return NewString("")
-}
-
-// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-
-func fnLocal(ell *Ell, args []V) (result []V, ok bool) {
-	if len(args) == 0 || args[0].Type != VTypeList {
-		return ell.Errorf("first argument must be a list")
-	}
-
-	// Duplicates or non-strings don't really matter to us, user's problem.
-	scope := ell.scopes[len(ell.scopes)-1]
-
-	values := args[1:]
-	for _, name := range args[0].List {
-		if len(values) > 0 {
-			scope[name.String] = *values[0].Clone()
-			values = values[1:]
-		}
-	}
-	return nil, true
-}
-
-func fnSet(ell *Ell, args []V) (result []V, ok bool) {
-	if len(args) == 0 || args[0].Type != VTypeString {
-		return ell.Errorf("first argument must be string")
-	}
-
-	if len(args) > 1 {
-		result = []V{*args[1].Clone()}
-		ell.Set(args[0].String, &result[0])
-		return result, true
-	}
-
-	// We return an empty list for a nil value.
-	if v := ell.Get(args[0].String); v != nil {
-		result = []V{*v.Clone()}
-	} else {
-		result = []V{*NewList(nil)}
-	}
-	return result, true
-}
-
-func fnList(ell *Ell, args []V) (result []V, ok bool) {
-	return []V{*NewList(args)}, true
-}
-
-func fnValues(ell *Ell, args []V) (result []V, ok bool) {
-	return args, true
-}
-
-func fnIf(ell *Ell, args []V) (result []V, ok bool) {
-	var cond, body, keyword int
-	for cond = 0; ; cond = keyword + 1 {
-		if cond >= len(args) {
-			return ell.Errorf("missing condition")
-		}
-		if body = cond + 1; body >= len(args) {
-			return ell.Errorf("missing body")
-		}
-
-		var res []V
-		if res, ok = EvalAny(ell, &args[cond], nil); !ok {
-			return nil, false
-		}
-		if len(res) > 0 && Truthy(&res[0]) {
-			return EvalAny(ell, &args[body], nil)
-		}
-
-		if keyword = body + 1; keyword >= len(args) {
-			break
-		}
-		if args[keyword].Type != VTypeString {
-			return ell.Errorf("expected keyword, got list")
-		}
-
-		switch kw := args[keyword].String; kw {
-		case "else":
-			if body = keyword + 1; body >= len(args) {
-				return ell.Errorf("missing body")
-			}
-			return EvalAny(ell, &args[body], nil)
-		case "elif":
-		default:
-			return ell.Errorf("invalid keyword: %s", kw)
-		}
-	}
-	return nil, true
-}
-
-func fnMap(ell *Ell, args []V) (result []V, ok bool) {
-	if len(args) < 1 {
-		return ell.Errorf("first argument must be a function")
-	}
-	if len(args) < 2 || args[0].Type != VTypeList {
-		return ell.Errorf("second argument must be a list")
-	}
-
-	body, values := &args[0], &args[1]
-	for _, v := range values.List {
-		res, ok := EvalAny(ell, body, &v)
-		if !ok {
-			return nil, false
-		}
-		result = append(result, res...)
-	}
-	return []V{*NewList(result)}, true
-}
-
-func fnPrint(ell *Ell, args []V) (result []V, ok bool) {
-	for _, arg := range args {
-		if arg.Type != VTypeString {
-			PrintV(os.Stdout, &arg)
-		} else if _, err := os.Stdout.WriteString(arg.String); err != nil {
-			return ell.Errorf("write failed: %s", err)
-		}
-	}
-	return nil, true
-}
-
-func fnCat(ell *Ell, args []V) (result []V, ok bool) {
-	buf := bytes.NewBuffer(nil)
-	for _, arg := range args {
-		if arg.Type != VTypeString {
-			PrintV(buf, &arg)
-		} else {
-			buf.WriteString(arg.String)
-		}
-	}
-	return []V{*NewString(buf.String())}, true
-}
-
-func fnSystem(ell *Ell, args []V) (result []V, ok bool) {
-	var argv []string
-	for _, arg := range args {
-		if arg.Type != VTypeString {
-			return ell.Errorf("arguments must be strings")
-		}
-		argv = append(argv, arg.String)
-	}
-	if len(argv) == 0 {
-		return ell.Errorf("command name required")
-	}
-
-	cmd := exec.Command(argv[0], argv[1:]...)
-	cmd.Stdin = os.Stdin
-	cmd.Stdout = os.Stdout
-	cmd.Stderr = os.Stderr
-
-	// Approximation of system(3) return value to match C ell at least a bit.
-	if err := cmd.Run(); err == nil {
-		return []V{*NewNumber(0)}, true
-	} else if _, ok := err.(*exec.Error); ok {
-		return ell.Errorf("%s", err)
-	} else {
-		return []V{*NewNumber(1)}, true
-	}
-}
-
-func fnParse(ell *Ell, args []V) (result []V, ok bool) {
-	if len(args) < 1 || args[0].Type != VTypeString {
-		return ell.Errorf("first argument must be string")
-	}
-
-	res, err := NewParser([]byte(args[0].String)).Run()
-	if err != nil {
-		return ell.Errorf("%s", err)
-	}
-	return []V{*NewList(res)}, true
-}
-
-func fnTry(ell *Ell, args []V) (result []V, ok bool) {
-	var body, handler *V
-	if len(args) < 1 {
-		return ell.Errorf("first argument must be a function")
-	}
-	if len(args) < 2 {
-		return ell.Errorf("second argument must be a function")
-	}
-	body, handler = &args[0], &args[1]
-	if result, ok = EvalAny(ell, body, nil); ok {
-		return
-	}
-
-	msg := NewString(ell.Error)
-	ell.Error = ""
-	return EvalAny(ell, handler, msg)
-}
-
-func fnThrow(ell *Ell, args []V) (result []V, ok bool) {
-	if len(args) < 1 || args[0].Type != VTypeString {
-		return ell.Errorf("first argument must be string")
-	}
-	return ell.Errorf("%s", args[0].String)
-}
-
-func fnPlus(ell *Ell, args []V) (result []V, ok bool) {
-	res := 0.
-	for _, arg := range args {
-		if arg.Type != VTypeString {
-			return ell.Errorf("arguments must be strings")
-		}
-		var value float64
-		if n, _ := fmt.Sscan(arg.String, &value); n < 1 {
-			return ell.Errorf("invalid number: %s", arg.String)
-		}
-		res += value
-	}
-	return []V{*NewNumber(res)}, true
-}
-
-func fnMinus(ell *Ell, args []V) (result []V, ok bool) {
-	if len(args) < 1 || args[0].Type != VTypeString {
-		return ell.Errorf("first argument must be string")
-	}
-
-	var res float64
-	if n, _ := fmt.Sscan(args[0].String, &res); n < 1 {
-		return ell.Errorf("invalid number: %f", args[0].String)
-	}
-	if len(args) == 1 {
-		res = -res
-	}
-
-	for _, arg := range args[1:] {
-		if arg.Type != VTypeString {
-			return ell.Errorf("arguments must be strings")
-		}
-		var value float64
-		if n, _ := fmt.Sscan(arg.String, &value); n < 1 {
-			return ell.Errorf("invalid number: %f", arg.String)
-		}
-		res -= value
-	}
-	return []V{*NewNumber(res)}, true
-}
-
-func fnMultiply(ell *Ell, args []V) (result []V, ok bool) {
-	res := 1.
-	for _, arg := range args {
-		if arg.Type != VTypeString {
-			return ell.Errorf("arguments must be strings")
-		}
-		var value float64
-		if n, _ := fmt.Sscan(arg.String, &value); n < 1 {
-			return ell.Errorf("invalid number: %s", arg.String)
-		}
-		res *= value
-	}
-	return []V{*NewNumber(res)}, true
-}
-
-func fnDivide(ell *Ell, args []V) (result []V, ok bool) {
-	if len(args) < 1 || args[0].Type != VTypeString {
-		return ell.Errorf("first argument must be string")
-	}
-
-	var res float64
-	if n, _ := fmt.Sscan(args[0].String, &res); n < 1 {
-		return ell.Errorf("invalid number: %f", args[0].String)
-	}
-	for _, arg := range args[1:] {
-		if arg.Type != VTypeString {
-			return ell.Errorf("arguments must be strings")
-		}
-		var value float64
-		if n, _ := fmt.Sscan(arg.String, &value); n < 1 {
-			return ell.Errorf("invalid number: %f", arg.String)
-		}
-		res /= value
-	}
-	return []V{*NewNumber(res)}, true
-}
-
-func fnNot(ell *Ell, args []V) (result []V, ok bool) {
-	if len(args) < 1 {
-		return ell.Errorf("missing argument")
-	}
-	return []V{*NewBoolean(!Truthy(&args[0]))}, true
-}
-
-func fnAnd(ell *Ell, args []V) (result []V, ok bool) {
-	if args == nil {
-		return []V{*NewBoolean(true)}, true
-	}
-	for _, arg := range args {
-		result, ok = EvalAny(ell, &arg, nil)
-		if !ok {
-			return nil, false
-		}
-		if len(result) < 1 || !Truthy(&result[0]) {
-			return []V{*NewBoolean(false)}, true
-		}
-	}
-	return result, true
-}
-
-func fnOr(ell *Ell, args []V) (result []V, ok bool) {
-	for _, arg := range args {
-		result, ok = EvalAny(ell, &arg, nil)
-		if !ok {
-			return nil, false
-		}
-		if len(result) > 0 && Truthy(&result[0]) {
-			return result, true
-		}
-	}
-	return []V{*NewBoolean(false)}, true
-}
-
-func fnEq(ell *Ell, args []V) (result []V, ok bool) {
-	if len(args) < 1 || args[0].Type != VTypeString {
-		return ell.Errorf("first argument must be string")
-	}
-	etalon, res := args[0].String, true
-	for _, arg := range args[1:] {
-		if arg.Type != VTypeString {
-			return ell.Errorf("arguments must be strings")
-		}
-		if res = etalon == arg.String; !res {
-			break
-		}
-	}
-	return []V{*NewBoolean(res)}, true
-}
-
-func fnLt(ell *Ell, args []V) (result []V, ok bool) {
-	if len(args) < 1 || args[0].Type != VTypeString {
-		return ell.Errorf("first argument must be string")
-	}
-	etalon, res := args[0].String, true
-	for _, arg := range args[1:] {
-		if arg.Type != VTypeString {
-			return ell.Errorf("arguments must be strings")
-		}
-		if res = etalon < arg.String; !res {
-			break
-		}
-		etalon = arg.String
-	}
-	return []V{*NewBoolean(res)}, true
-}
-
-func fnEquals(ell *Ell, args []V) (result []V, ok bool) {
-	if len(args) < 1 || args[0].Type != VTypeString {
-		return ell.Errorf("first argument must be string")
-	}
-	var first, second float64
-	if n, _ := fmt.Sscan(args[0].String, &first); n < 1 {
-		return ell.Errorf("invalid number: %f", args[0].String)
-	}
-	res := true
-	for _, arg := range args[1:] {
-		if arg.Type != VTypeString {
-			return ell.Errorf("arguments must be strings")
-		}
-		if n, _ := fmt.Sscan(arg.String, &second); n < 1 {
-			return ell.Errorf("invalid number: %f", arg.String)
-		}
-		if res = first == second; !res {
-			break
-		}
-		first = second
-	}
-	return []V{*NewBoolean(res)}, true
-}
-
-func fnLess(ell *Ell, args []V) (result []V, ok bool) {
-	if len(args) < 1 || args[0].Type != VTypeString {
-		return ell.Errorf("first argument must be string")
-	}
-	var first, second float64
-	if n, _ := fmt.Sscan(args[0].String, &first); n < 1 {
-		return ell.Errorf("invalid number: %f", args[0].String)
-	}
-	res := true
-	for _, arg := range args[1:] {
-		if arg.Type != VTypeString {
-			return ell.Errorf("arguments must be strings")
-		}
-		if n, _ := fmt.Sscan(arg.String, &second); n < 1 {
-			return ell.Errorf("invalid number: %f", arg.String)
-		}
-		if res = first < second; !res {
-			break
-		}
-		first = second
-	}
-	return []V{*NewBoolean(res)}, true
-}
-
-// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-
-var stdNative = map[string]Handler{
-	"local":  fnLocal,
-	"set":    fnSet,
-	"list":   fnList,
-	"values": fnValues,
-	"if":     fnIf,
-	"map":    fnMap,
-	"print":  fnPrint,
-	"..":     fnCat,
-	"system": fnSystem,
-	"parse":  fnParse,
-	"try":    fnTry,
-	"throw":  fnThrow,
-	"+":      fnPlus,
-	"-":      fnMinus,
-	"*":      fnMultiply,
-	"/":      fnDivide,
-	"not":    fnNot,
-	"and":    fnAnd,
-	"or":     fnOr,
-	"eq?":    fnEq,
-	"lt?":    fnLt,
-	"=":      fnEquals,
-	"<":      fnLess,
-}
-
-var stdComposed = `
-set unless { if (not (@1)) @2 }
-set filter { local [_body _list] @1 @2;
- map { if (@_body @1) { @1 } } @_list }
-set for { local [_list _body] @1 @2;
- try { map { @_body @1 } @_list } { if (ne? @1 _break) { throw @1 } } }
-
-set break { throw _break }
-
-# TODO: we should be able to apply them to all arguments
-set ne? { not (eq? @1 @2) }; set le? { ge? @2 @1 }
-set ge? { not (lt? @1 @2) }; set gt? { lt? @2 @1 }
-set <>  { not (= @1 @2)   }; set <=  { >= @2 @1  }
-set >=  { not (< @1 @2)   }; set >   { <  @2 @1  }`
-
-// StdInitialize initializes the ell standard library.
-func StdInitialize(ell *Ell) bool {
-	for name, handler := range stdNative {
-		ell.Native[name] = handler
-	}
-
-	p := NewParser([]byte(stdComposed))
-	program, err := p.Run()
-	if err != nil {
-		return false
-	}
-
-	_, ok := ell.EvalBlock(program, nil)
-	return ok
-}
diff --git a/ell/stdlib.go b/ell/stdlib.go
new file mode 100644
index 0000000..f91e721
--- /dev/null
+++ b/ell/stdlib.go
@@ -0,0 +1,513 @@
+//
+// Copyright (c) 2018, Přemysl Janouch <p@janouch.name>
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+//
+
+package ell
+
+import (
+	"bytes"
+	"fmt"
+	"os"
+	"os/exec"
+)
+
+// --- Standard library --------------------------------------------------------
+
+// EvalAny evaluates any value and appends to the result.
+func EvalAny(ell *Ell, body *V, arg *V) (result []V, ok bool) {
+	if body.Type == VTypeString {
+		return []V{*body}, true
+	}
+	var args []V
+	if arg != nil {
+		args = append(args, *arg.Clone())
+	}
+	if res, ok := ell.EvalBlock(body.List, args); ok {
+		return res, true
+	}
+	return nil, false
+}
+
+// NewNumber creates a new string value containing a number.
+func NewNumber(n float64) *V {
+	s := fmt.Sprintf("%f", n)
+	i := len(s)
+	for i > 0 && s[i-1] == '0' {
+		i--
+	}
+	if s[i-1] == '.' {
+		i--
+	}
+	return NewString(s[:i])
+}
+
+// Truthy decides whether any value is logically true.
+func Truthy(v *V) bool {
+	return v != nil && (len(v.List) > 0 || len(v.String) > 0)
+}
+
+// NewBoolean creates a new string value copying the boolean's truthiness.
+func NewBoolean(b bool) *V {
+	if b {
+		return NewString("1")
+	}
+	return NewString("")
+}
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+func fnLocal(ell *Ell, args []V) (result []V, ok bool) {
+	if len(args) == 0 || args[0].Type != VTypeList {
+		return ell.Errorf("first argument must be a list")
+	}
+
+	// Duplicates or non-strings don't really matter to us, user's problem.
+	scope := ell.scopes[len(ell.scopes)-1]
+
+	values := args[1:]
+	for _, name := range args[0].List {
+		if len(values) > 0 {
+			scope[name.String] = *values[0].Clone()
+			values = values[1:]
+		}
+	}
+	return nil, true
+}
+
+func fnSet(ell *Ell, args []V) (result []V, ok bool) {
+	if len(args) == 0 || args[0].Type != VTypeString {
+		return ell.Errorf("first argument must be string")
+	}
+
+	if len(args) > 1 {
+		result = []V{*args[1].Clone()}
+		ell.Set(args[0].String, &result[0])
+		return result, true
+	}
+
+	// We return an empty list for a nil value.
+	if v := ell.Get(args[0].String); v != nil {
+		result = []V{*v.Clone()}
+	} else {
+		result = []V{*NewList(nil)}
+	}
+	return result, true
+}
+
+func fnList(ell *Ell, args []V) (result []V, ok bool) {
+	return []V{*NewList(args)}, true
+}
+
+func fnValues(ell *Ell, args []V) (result []V, ok bool) {
+	return args, true
+}
+
+func fnIf(ell *Ell, args []V) (result []V, ok bool) {
+	var cond, body, keyword int
+	for cond = 0; ; cond = keyword + 1 {
+		if cond >= len(args) {
+			return ell.Errorf("missing condition")
+		}
+		if body = cond + 1; body >= len(args) {
+			return ell.Errorf("missing body")
+		}
+
+		var res []V
+		if res, ok = EvalAny(ell, &args[cond], nil); !ok {
+			return nil, false
+		}
+		if len(res) > 0 && Truthy(&res[0]) {
+			return EvalAny(ell, &args[body], nil)
+		}
+
+		if keyword = body + 1; keyword >= len(args) {
+			break
+		}
+		if args[keyword].Type != VTypeString {
+			return ell.Errorf("expected keyword, got list")
+		}
+
+		switch kw := args[keyword].String; kw {
+		case "else":
+			if body = keyword + 1; body >= len(args) {
+				return ell.Errorf("missing body")
+			}
+			return EvalAny(ell, &args[body], nil)
+		case "elif":
+		default:
+			return ell.Errorf("invalid keyword: %s", kw)
+		}
+	}
+	return nil, true
+}
+
+func fnMap(ell *Ell, args []V) (result []V, ok bool) {
+	if len(args) < 1 {
+		return ell.Errorf("first argument must be a function")
+	}
+	if len(args) < 2 || args[0].Type != VTypeList {
+		return ell.Errorf("second argument must be a list")
+	}
+
+	body, values := &args[0], &args[1]
+	for _, v := range values.List {
+		res, ok := EvalAny(ell, body, &v)
+		if !ok {
+			return nil, false
+		}
+		result = append(result, res...)
+	}
+	return []V{*NewList(result)}, true
+}
+
+func fnPrint(ell *Ell, args []V) (result []V, ok bool) {
+	for _, arg := range args {
+		if arg.Type != VTypeString {
+			PrintV(os.Stdout, &arg)
+		} else if _, err := os.Stdout.WriteString(arg.String); err != nil {
+			return ell.Errorf("write failed: %s", err)
+		}
+	}
+	return nil, true
+}
+
+func fnCat(ell *Ell, args []V) (result []V, ok bool) {
+	buf := bytes.NewBuffer(nil)
+	for _, arg := range args {
+		if arg.Type != VTypeString {
+			PrintV(buf, &arg)
+		} else {
+			buf.WriteString(arg.String)
+		}
+	}
+	return []V{*NewString(buf.String())}, true
+}
+
+func fnSystem(ell *Ell, args []V) (result []V, ok bool) {
+	var argv []string
+	for _, arg := range args {
+		if arg.Type != VTypeString {
+			return ell.Errorf("arguments must be strings")
+		}
+		argv = append(argv, arg.String)
+	}
+	if len(argv) == 0 {
+		return ell.Errorf("command name required")
+	}
+
+	cmd := exec.Command(argv[0], argv[1:]...)
+	cmd.Stdin = os.Stdin
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+
+	// Approximation of system(3) return value to match C ell at least a bit.
+	if err := cmd.Run(); err == nil {
+		return []V{*NewNumber(0)}, true
+	} else if _, ok := err.(*exec.Error); ok {
+		return ell.Errorf("%s", err)
+	} else {
+		return []V{*NewNumber(1)}, true
+	}
+}
+
+func fnParse(ell *Ell, args []V) (result []V, ok bool) {
+	if len(args) < 1 || args[0].Type != VTypeString {
+		return ell.Errorf("first argument must be string")
+	}
+
+	res, err := NewParser([]byte(args[0].String)).Run()
+	if err != nil {
+		return ell.Errorf("%s", err)
+	}
+	return []V{*NewList(res)}, true
+}
+
+func fnTry(ell *Ell, args []V) (result []V, ok bool) {
+	var body, handler *V
+	if len(args) < 1 {
+		return ell.Errorf("first argument must be a function")
+	}
+	if len(args) < 2 {
+		return ell.Errorf("second argument must be a function")
+	}
+	body, handler = &args[0], &args[1]
+	if result, ok = EvalAny(ell, body, nil); ok {
+		return
+	}
+
+	msg := NewString(ell.Error)
+	ell.Error = ""
+	return EvalAny(ell, handler, msg)
+}
+
+func fnThrow(ell *Ell, args []V) (result []V, ok bool) {
+	if len(args) < 1 || args[0].Type != VTypeString {
+		return ell.Errorf("first argument must be string")
+	}
+	return ell.Errorf("%s", args[0].String)
+}
+
+func fnPlus(ell *Ell, args []V) (result []V, ok bool) {
+	res := 0.
+	for _, arg := range args {
+		if arg.Type != VTypeString {
+			return ell.Errorf("arguments must be strings")
+		}
+		var value float64
+		if n, _ := fmt.Sscan(arg.String, &value); n < 1 {
+			return ell.Errorf("invalid number: %s", arg.String)
+		}
+		res += value
+	}
+	return []V{*NewNumber(res)}, true
+}
+
+func fnMinus(ell *Ell, args []V) (result []V, ok bool) {
+	if len(args) < 1 || args[0].Type != VTypeString {
+		return ell.Errorf("first argument must be string")
+	}
+
+	var res float64
+	if n, _ := fmt.Sscan(args[0].String, &res); n < 1 {
+		return ell.Errorf("invalid number: %f", args[0].String)
+	}
+	if len(args) == 1 {
+		res = -res
+	}
+
+	for _, arg := range args[1:] {
+		if arg.Type != VTypeString {
+			return ell.Errorf("arguments must be strings")
+		}
+		var value float64
+		if n, _ := fmt.Sscan(arg.String, &value); n < 1 {
+			return ell.Errorf("invalid number: %f", arg.String)
+		}
+		res -= value
+	}
+	return []V{*NewNumber(res)}, true
+}
+
+func fnMultiply(ell *Ell, args []V) (result []V, ok bool) {
+	res := 1.
+	for _, arg := range args {
+		if arg.Type != VTypeString {
+			return ell.Errorf("arguments must be strings")
+		}
+		var value float64
+		if n, _ := fmt.Sscan(arg.String, &value); n < 1 {
+			return ell.Errorf("invalid number: %s", arg.String)
+		}
+		res *= value
+	}
+	return []V{*NewNumber(res)}, true
+}
+
+func fnDivide(ell *Ell, args []V) (result []V, ok bool) {
+	if len(args) < 1 || args[0].Type != VTypeString {
+		return ell.Errorf("first argument must be string")
+	}
+
+	var res float64
+	if n, _ := fmt.Sscan(args[0].String, &res); n < 1 {
+		return ell.Errorf("invalid number: %f", args[0].String)
+	}
+	for _, arg := range args[1:] {
+		if arg.Type != VTypeString {
+			return ell.Errorf("arguments must be strings")
+		}
+		var value float64
+		if n, _ := fmt.Sscan(arg.String, &value); n < 1 {
+			return ell.Errorf("invalid number: %f", arg.String)
+		}
+		res /= value
+	}
+	return []V{*NewNumber(res)}, true
+}
+
+func fnNot(ell *Ell, args []V) (result []V, ok bool) {
+	if len(args) < 1 {
+		return ell.Errorf("missing argument")
+	}
+	return []V{*NewBoolean(!Truthy(&args[0]))}, true
+}
+
+func fnAnd(ell *Ell, args []V) (result []V, ok bool) {
+	if args == nil {
+		return []V{*NewBoolean(true)}, true
+	}
+	for _, arg := range args {
+		result, ok = EvalAny(ell, &arg, nil)
+		if !ok {
+			return nil, false
+		}
+		if len(result) < 1 || !Truthy(&result[0]) {
+			return []V{*NewBoolean(false)}, true
+		}
+	}
+	return result, true
+}
+
+func fnOr(ell *Ell, args []V) (result []V, ok bool) {
+	for _, arg := range args {
+		result, ok = EvalAny(ell, &arg, nil)
+		if !ok {
+			return nil, false
+		}
+		if len(result) > 0 && Truthy(&result[0]) {
+			return result, true
+		}
+	}
+	return []V{*NewBoolean(false)}, true
+}
+
+func fnEq(ell *Ell, args []V) (result []V, ok bool) {
+	if len(args) < 1 || args[0].Type != VTypeString {
+		return ell.Errorf("first argument must be string")
+	}
+	etalon, res := args[0].String, true
+	for _, arg := range args[1:] {
+		if arg.Type != VTypeString {
+			return ell.Errorf("arguments must be strings")
+		}
+		if res = etalon == arg.String; !res {
+			break
+		}
+	}
+	return []V{*NewBoolean(res)}, true
+}
+
+func fnLt(ell *Ell, args []V) (result []V, ok bool) {
+	if len(args) < 1 || args[0].Type != VTypeString {
+		return ell.Errorf("first argument must be string")
+	}
+	etalon, res := args[0].String, true
+	for _, arg := range args[1:] {
+		if arg.Type != VTypeString {
+			return ell.Errorf("arguments must be strings")
+		}
+		if res = etalon < arg.String; !res {
+			break
+		}
+		etalon = arg.String
+	}
+	return []V{*NewBoolean(res)}, true
+}
+
+func fnEquals(ell *Ell, args []V) (result []V, ok bool) {
+	if len(args) < 1 || args[0].Type != VTypeString {
+		return ell.Errorf("first argument must be string")
+	}
+	var first, second float64
+	if n, _ := fmt.Sscan(args[0].String, &first); n < 1 {
+		return ell.Errorf("invalid number: %f", args[0].String)
+	}
+	res := true
+	for _, arg := range args[1:] {
+		if arg.Type != VTypeString {
+			return ell.Errorf("arguments must be strings")
+		}
+		if n, _ := fmt.Sscan(arg.String, &second); n < 1 {
+			return ell.Errorf("invalid number: %f", arg.String)
+		}
+		if res = first == second; !res {
+			break
+		}
+		first = second
+	}
+	return []V{*NewBoolean(res)}, true
+}
+
+func fnLess(ell *Ell, args []V) (result []V, ok bool) {
+	if len(args) < 1 || args[0].Type != VTypeString {
+		return ell.Errorf("first argument must be string")
+	}
+	var first, second float64
+	if n, _ := fmt.Sscan(args[0].String, &first); n < 1 {
+		return ell.Errorf("invalid number: %f", args[0].String)
+	}
+	res := true
+	for _, arg := range args[1:] {
+		if arg.Type != VTypeString {
+			return ell.Errorf("arguments must be strings")
+		}
+		if n, _ := fmt.Sscan(arg.String, &second); n < 1 {
+			return ell.Errorf("invalid number: %f", arg.String)
+		}
+		if res = first < second; !res {
+			break
+		}
+		first = second
+	}
+	return []V{*NewBoolean(res)}, true
+}
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+var stdNative = map[string]Handler{
+	"local":  fnLocal,
+	"set":    fnSet,
+	"list":   fnList,
+	"values": fnValues,
+	"if":     fnIf,
+	"map":    fnMap,
+	"print":  fnPrint,
+	"..":     fnCat,
+	"system": fnSystem,
+	"parse":  fnParse,
+	"try":    fnTry,
+	"throw":  fnThrow,
+	"+":      fnPlus,
+	"-":      fnMinus,
+	"*":      fnMultiply,
+	"/":      fnDivide,
+	"not":    fnNot,
+	"and":    fnAnd,
+	"or":     fnOr,
+	"eq?":    fnEq,
+	"lt?":    fnLt,
+	"=":      fnEquals,
+	"<":      fnLess,
+}
+
+var stdComposed = `
+set unless { if (not (@1)) @2 }
+set filter { local [_body _list] @1 @2;
+ map { if (@_body @1) { @1 } } @_list }
+set for { local [_list _body] @1 @2;
+ try { map { @_body @1 } @_list } { if (ne? @1 _break) { throw @1 } } }
+
+set break { throw _break }
+
+# TODO: we should be able to apply them to all arguments
+set ne? { not (eq? @1 @2) }; set le? { ge? @2 @1 }
+set ge? { not (lt? @1 @2) }; set gt? { lt? @2 @1 }
+set <>  { not (= @1 @2)   }; set <=  { >= @2 @1  }
+set >=  { not (< @1 @2)   }; set >   { <  @2 @1  }`
+
+// StdInitialize initializes the ell standard library.
+func StdInitialize(ell *Ell) bool {
+	for name, handler := range stdNative {
+		ell.Native[name] = handler
+	}
+
+	p := NewParser([]byte(stdComposed))
+	program, err := p.Run()
+	if err != nil {
+		return false
+	}
+
+	_, ok := ell.EvalBlock(program, nil)
+	return ok
+}