FORTH-ish interpreter
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prosper/eval.go

95 lines
2.4 KiB

package main
import (
"fmt"
"io"
"strconv"
"strings"
)
// Context is a set of Dictionary + Stacks + Flags representing a runtime environment
type Context struct {
Dictionary Dictionary
Stack *Stack // main stack
RStack *Stack // "return" stack, for handling loops/backward jumps
IfStack *Stack // tracks nested branches
Flags Flags
Words []string
Memory Memory
StringBuffer string
Output io.Writer
}
// 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)
// if we're not in immedate mode, and the word isn't immediate, add word to buffer and continue parsing
if !c.Flags.GetFlag("Immediate") && !w.Immediate {
c.Words = append(c.Words, sword)
word = []byte{}
continue
}
ifcheck, _ := c.IfStack.Pick(0)
if len(c.IfStack.values) == 0 || (len(c.IfStack.values) > 0 && ifcheck == 1) || w.BranchCheck {
// run word
c.RStack.Push(i)
err := c.Exec(w, line[i:])
if 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, s string) error {
if w.Impl != nil {
// we have an implementation for that word. Run it.
err := w.Impl(s)
if err != nil {
return fmt.Errorf("error during built-in: %w", err)
}
} else if len(w.Source) != 0 {
// user-defined word; let's descend...
err := c.Eval(strings.Join(w.Source, " ") + " ")
if err != nil {
return fmt.Errorf("error during nested evaluation of word %+v: %w", w, err)
}
} else if w.Variable > 0 {
// it's a variable, let's get that address and put it on the stack
c.Stack.Push(w.Variable)
} else {
it, err := strconv.Atoi(w.Name)
if err == nil {
// it was a number! put it on the stack.
c.Stack.Push(it)
} else {
return fmt.Errorf("unable to parse word %s", w.Name)
}
}
return nil
}