prosper/eval.go

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package main
import (
"fmt"
"strconv"
"strings"
)
// Context is a set of Dictionary + Stacks representing a runtime environment
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type Context struct {
Dictionary Dictionary
Stack *Stack
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RStack *Stack
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}
// Eval evaulates a given line, recursively descending into given words as needed
func (c *Context) Eval(line string) error {
// state
var word []byte
var words []string
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var comment bool
immediate := true
for i := 0; i < len(line); i = i + 1 {
switch line[i] {
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case '(', ')': // comments
if len(word) == 0 {
if line[i] == '(' {
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comment = true
continue
}
comment = false
continue
} else {
word = append(word, line[i])
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}
case ':', ';': // COMPILE/IMMEDIATE mode swapping
if len(word) == 0 {
if line[i] == ':' {
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immediate = false
} else if line[i-1] == ' ' && line[i] == ';' {
c.Dictionary.AddWord(words[0], nil, words[1:])
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word = []byte{}
immediate = true
}
} else {
word = append(word, line[i])
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}
case ' ':
if !immediate { // continue building our subroutine if we're not in immediate mode...
if len(word) != 0 { // don't add empty words to our list
words = append(words, strings.TrimSpace(string(word)))
word = []byte{}
}
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continue
}
if len(word) == 0 || comment {
// empty space, just continue...
continue
}
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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
}
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// 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 len(w.Source) != 0 {
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// user-defined word; let's descend...
c.RStack.Push(i)
err := c.Eval(strings.Join(w.Source, " ") + " ")
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if err != nil {
return err
}
i, err = c.RStack.Pop()
if err != nil {
return fmt.Errorf("error while popping from return stack: %v", err)
}
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word = []byte{}
}
default:
if !comment {
word = append(word, line[i])
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}
}
}
return nil
}