prosper/eval.go

package main

import (
	"fmt"
	"strconv"
	"strings"
)

// Context is a set of Dictionary + Stack representing a runtime environment
type Context struct {
	Dictionary Dictionary
	Stack      *Stack
	RStack     *Stack
}

// Eval evaulates a given line, recursively descending into given words as needed
func (c *Context) Eval(line string) error {
	// state
	var word []byte
	var comment bool
	immediate := true

	for i := 0; i < len(line); i = i + 1 {
		switch line[i] {
		case '(', ')': // comments
			if len(word) == 0 {
				if line[i] == '(' {
					comment = true
					continue
				}
				comment = false
				continue
			} else {
				word = append(word, line[i])
			}
		case ':', ';': // COMPILE/IMMEDIATE mode swapping
			if len(word) == 0 {
				if line[i] == ':' {
					immediate = false
				}
			} else {
				if line[i-1] == ' ' && line[i] == ';' {
					def := strings.SplitN(strings.TrimSpace(string(word)), " ", 2)
					c.Dictionary.AddWord(def[0], nil, def[1]+" ")
					word = []byte{}
					immediate = true
				} else {
					word = append(word, line[i])
				}
			}
		case ' ':
			if !immediate { // continue building our subroutine if we're not in immediate mode...
				word = append(word, line[i])
				continue
			}
			if len(word) == 0 || comment {
				// empty space, just continue...
				continue
			}
			int, err := strconv.Atoi(string(word))
			if err == nil {
				// it was a number! put it on the stack.
				c.Stack.Push(int)
				word = []byte{}
				continue
			}
			// it wasn't a number. Is it a word we know?
			w, err := c.Dictionary.GetWord(string(word))
			if err != nil {
				return fmt.Errorf("could not parse %s; %v", w.Name, err)
			}
			if w.Impl != nil {
				// we have an implementation for that word. Run it.
				err := w.Impl()
				if err != nil {
					return err
				}
				word = []byte{}
			} else if w.Source != "" {
				// user-defined word; let's descend...
				err := c.Eval(w.Source)
				if err != nil {
					return err
				}
				word = []byte{}
			}
		default:
			if !comment {
				word = append(word, line[i])
			}
		}
	}

	return nil
}