1 files changed, 81 insertions, 0 deletions
diff --git a/src/StringRacer.kt b/src/StringRacer.kt
new file mode 100644
index 0000000..d0a4a15
--- /dev/null
+++ b/src/StringRacer.kt
@@ -0,0 +1,81 @@
+package moe.nea.lisp
+
+import java.util.*
+
+class StringRacer(val filename: String, val backing: String) {
+    var idx = 0
+    val stack = Stack<Int>()
+
+    fun pushState() {
+        stack.push(idx)
+    }
+
+    fun popState() {
+        idx = stack.pop()
+    }
+
+    fun span(start: Int) = LispPosition(start, idx, filename, backing)
+
+    fun discardState() {
+        stack.pop()
+    }
+
+    fun peek(count: Int): String {
+        return backing.substring(minOf(idx, backing.length), minOf(idx + count, backing.length))
+    }
+
+    fun finished(): Boolean {
+        return peek(1).isEmpty()
+    }
+
+    fun peekReq(count: Int): String? {
+        val p = peek(count)
+        if (p.length != count)
+            return null
+        return p
+    }
+
+    fun consumeCountReq(count: Int): String? {
+        val p = peekReq(count)
+        if (p != null)
+            idx += count
+        return p
+    }
+
+    fun tryConsume(string: String): Boolean {
+        val p = peek(string.length)
+        if (p != string)
+            return false
+        idx += p.length
+        return true
+    }
+
+    fun consumeWhile(shouldConsumeThisString: (String) -> Boolean): String {
+        var lastString: String = ""
+        while (true) {
+            val nextPart = peek(1)
+            if (nextPart.isEmpty()) break
+            val nextString = lastString + nextPart
+            if (!shouldConsumeThisString(nextString)) {
+                break
+            }
+            idx++
+            lastString = nextString
+        }
+        return lastString
+    }
+
+    fun expect(search: String, errorMessage: String) {
+        if (!tryConsume(search))
+            error(errorMessage)
+    }
+
+    fun error(errorMessage: String): Nothing {
+        throw LispParsingError(backing, idx, errorMessage)
+    }
+
+    fun skipWhitespace() {
+        consumeWhile { Character.isWhitespace(it.last()) }
+    }
+}
+