1 files changed, 251 insertions, 0 deletions
diff --git a/core/parse/dispenser.go b/core/parse/dispenser.go
new file mode 100644
index 000000000..08aa6e76d
--- /dev/null
+++ b/core/parse/dispenser.go
@@ -0,0 +1,251 @@
+package parse
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"strings"
+)
+
+// Dispenser is a type that dispenses tokens, similarly to a lexer,
+// except that it can do so with some notion of structure and has
+// some really convenient methods.
+type Dispenser struct {
+	filename string
+	tokens   []token
+	cursor   int
+	nesting  int
+}
+
+// NewDispenser returns a Dispenser, ready to use for parsing the given input.
+func NewDispenser(filename string, input io.Reader) Dispenser {
+	return Dispenser{
+		filename: filename,
+		tokens:   allTokens(input),
+		cursor:   -1,
+	}
+}
+
+// NewDispenserTokens returns a Dispenser filled with the given tokens.
+func NewDispenserTokens(filename string, tokens []token) Dispenser {
+	return Dispenser{
+		filename: filename,
+		tokens:   tokens,
+		cursor:   -1,
+	}
+}
+
+// Next loads the next token. Returns true if a token
+// was loaded; false otherwise. If false, all tokens
+// have been consumed.
+func (d *Dispenser) Next() bool {
+	if d.cursor < len(d.tokens)-1 {
+		d.cursor++
+		return true
+	}
+	return false
+}
+
+// NextArg loads the next token if it is on the same
+// line. Returns true if a token was loaded; false
+// otherwise. If false, all tokens on the line have
+// been consumed. It handles imported tokens correctly.
+func (d *Dispenser) NextArg() bool {
+	if d.cursor < 0 {
+		d.cursor++
+		return true
+	}
+	if d.cursor >= len(d.tokens) {
+		return false
+	}
+	if d.cursor < len(d.tokens)-1 &&
+		d.tokens[d.cursor].file == d.tokens[d.cursor+1].file &&
+		d.tokens[d.cursor].line+d.numLineBreaks(d.cursor) == d.tokens[d.cursor+1].line {
+		d.cursor++
+		return true
+	}
+	return false
+}
+
+// NextLine loads the next token only if it is not on the same
+// line as the current token, and returns true if a token was
+// loaded; false otherwise. If false, there is not another token
+// or it is on the same line. It handles imported tokens correctly.
+func (d *Dispenser) NextLine() bool {
+	if d.cursor < 0 {
+		d.cursor++
+		return true
+	}
+	if d.cursor >= len(d.tokens) {
+		return false
+	}
+	if d.cursor < len(d.tokens)-1 &&
+		(d.tokens[d.cursor].file != d.tokens[d.cursor+1].file ||
+			d.tokens[d.cursor].line+d.numLineBreaks(d.cursor) < d.tokens[d.cursor+1].line) {
+		d.cursor++
+		return true
+	}
+	return false
+}
+
+// NextBlock can be used as the condition of a for loop
+// to load the next token as long as it opens a block or
+// is already in a block. It returns true if a token was
+// loaded, or false when the block's closing curly brace
+// was loaded and thus the block ended. Nested blocks are
+// not supported.
+func (d *Dispenser) NextBlock() bool {
+	if d.nesting > 0 {
+		d.Next()
+		if d.Val() == "}" {
+			d.nesting--
+			return false
+		}
+		return true
+	}
+	if !d.NextArg() { // block must open on same line
+		return false
+	}
+	if d.Val() != "{" {
+		d.cursor-- // roll back if not opening brace
+		return false
+	}
+	d.Next()
+	if d.Val() == "}" {
+		// Open and then closed right away
+		return false
+	}
+	d.nesting++
+	return true
+}
+
+// IncrNest adds a level of nesting to the dispenser.
+func (d *Dispenser) IncrNest() {
+	d.nesting++
+	return
+}
+
+// Val gets the text of the current token. If there is no token
+// loaded, it returns empty string.
+func (d *Dispenser) Val() string {
+	if d.cursor < 0 || d.cursor >= len(d.tokens) {
+		return ""
+	}
+	return d.tokens[d.cursor].text
+}
+
+// Line gets the line number of the current token. If there is no token
+// loaded, it returns 0.
+func (d *Dispenser) Line() int {
+	if d.cursor < 0 || d.cursor >= len(d.tokens) {
+		return 0
+	}
+	return d.tokens[d.cursor].line
+}
+
+// File gets the filename of the current token. If there is no token loaded,
+// it returns the filename originally given when parsing started.
+func (d *Dispenser) File() string {
+	if d.cursor < 0 || d.cursor >= len(d.tokens) {
+		return d.filename
+	}
+	if tokenFilename := d.tokens[d.cursor].file; tokenFilename != "" {
+		return tokenFilename
+	}
+	return d.filename
+}
+
+// Args is a convenience function that loads the next arguments
+// (tokens on the same line) into an arbitrary number of strings
+// pointed to in targets. If there are fewer tokens available
+// than string pointers, the remaining strings will not be changed
+// and false will be returned. If there were enough tokens available
+// to fill the arguments, then true will be returned.
+func (d *Dispenser) Args(targets ...*string) bool {
+	enough := true
+	for i := 0; i < len(targets); i++ {
+		if !d.NextArg() {
+			enough = false
+			break
+		}
+		*targets[i] = d.Val()
+	}
+	return enough
+}
+
+// RemainingArgs loads any more arguments (tokens on the same line)
+// into a slice and returns them. Open curly brace tokens also indicate
+// the end of arguments, and the curly brace is not included in
+// the return value nor is it loaded.
+func (d *Dispenser) RemainingArgs() []string {
+	var args []string
+
+	for d.NextArg() {
+		if d.Val() == "{" {
+			d.cursor--
+			break
+		}
+		args = append(args, d.Val())
+	}
+
+	return args
+}
+
+// ArgErr returns an argument error, meaning that another
+// argument was expected but not found. In other words,
+// a line break or open curly brace was encountered instead of
+// an argument.
+func (d *Dispenser) ArgErr() error {
+	if d.Val() == "{" {
+		return d.Err("Unexpected token '{', expecting argument")
+	}
+	return d.Errf("Wrong argument count or unexpected line ending after '%s'", d.Val())
+}
+
+// SyntaxErr creates a generic syntax error which explains what was
+// found and what was expected.
+func (d *Dispenser) SyntaxErr(expected string) error {
+	msg := fmt.Sprintf("%s:%d - Syntax error: Unexpected token '%s', expecting '%s'", d.File(), d.Line(), d.Val(), expected)
+	return errors.New(msg)
+}
+
+// EOFErr returns an error indicating that the dispenser reached
+// the end of the input when searching for the next token.
+func (d *Dispenser) EOFErr() error {
+	return d.Errf("Unexpected EOF")
+}
+
+// Err generates a custom parse error with a message of msg.
+func (d *Dispenser) Err(msg string) error {
+	msg = fmt.Sprintf("%s:%d - Parse error: %s", d.File(), d.Line(), msg)
+	return errors.New(msg)
+}
+
+// Errf is like Err, but for formatted error messages
+func (d *Dispenser) Errf(format string, args ...interface{}) error {
+	return d.Err(fmt.Sprintf(format, args...))
+}
+
+// numLineBreaks counts how many line breaks are in the token
+// value given by the token index tknIdx. It returns 0 if the
+// token does not exist or there are no line breaks.
+func (d *Dispenser) numLineBreaks(tknIdx int) int {
+	if tknIdx < 0 || tknIdx >= len(d.tokens) {
+		return 0
+	}
+	return strings.Count(d.tokens[tknIdx].text, "\n")
+}
+
+// isNewLine determines whether the current token is on a different
+// line (higher line number) than the previous token. It handles imported
+// tokens correctly. If there isn't a previous token, it returns true.
+func (d *Dispenser) isNewLine() bool {
+	if d.cursor < 1 {
+		return true
+	}
+	if d.cursor > len(d.tokens)-1 {
+		return false
+	}
+	return d.tokens[d.cursor-1].file != d.tokens[d.cursor].file ||
+		d.tokens[d.cursor-1].line+d.numLineBreaks(d.cursor-1) < d.tokens[d.cursor].line
+}