FORTH-ish interpreter
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prosper/eval.go

93 lines
2.0 KiB

package main
import (
"fmt"
"strconv"
"strings"
)
// Context is a set of Dictionary + Stacks + Flags representing a runtime environment
type Context struct {
Dictionary Dictionary
Stack *Stack
RStack *Stack
Flags Flags
Words []string
}
// Eval evaulates a given line, recursively descending into given words as needed
func (c *Context) Eval(line string) error {
// state
var word []byte
for i := 0; i < len(line); i = i + 1 {
switch line[i] {
case ' ':
sword := strings.TrimSpace(string(word))
if len(word) == 0 {
// empty space, just continue...
continue
}
// Is this a word we know?
w, _ := c.Dictionary.GetWord(sword)
// check if it's an IMMEDIATE mode toggle word
if !c.Flags.GetFlag("Immediate") {
c.Flags.SetFlag("Immediate", w.Immediate)
}
if !c.Flags.GetFlag("Immediate") {
if !c.Flags.GetFlag("Comment") {
c.Words = append(c.Words, sword)
}
word = []byte{}
continue
}
int, err := strconv.Atoi(sword)
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(sword)
if err != nil {
return fmt.Errorf("could not parse %s; %v", w.Name, err)
}
// run word
c.RStack.Push(i)
if err = c.Exec(w); err != nil {
return err
}
i, err = c.RStack.Pop()
if err != nil {
return fmt.Errorf("error while popping from return stack: %v", err)
}
word = []byte{}
default:
word = append(word, line[i])
}
}
return nil
}
// Exec wraps the branched execution of words (either built-in or user-defined)
func (c *Context) Exec(w Word) error {
if w.Impl != nil {
// we have an implementation for that word. Run it.
err := w.Impl()
if err != nil {
return err
}
} else if len(w.Source) != 0 {
// user-defined word; let's descend...
err := c.Eval(strings.Join(w.Source, " ") + " ")
if err != nil {
return err
}
}
return nil
}