feat(parser): Terms parsing

src/better_parser/SimplePrologParser.kt

@@ -0,0 +1,61 @@
+package better_parser
+
+import com.github.h0tk3y.betterParse.combinators.*
+import com.github.h0tk3y.betterParse.grammar.Grammar
+import com.github.h0tk3y.betterParse.grammar.parser
+import com.github.h0tk3y.betterParse.lexer.Token
+import com.github.h0tk3y.betterParse.lexer.literalToken
+import com.github.h0tk3y.betterParse.lexer.regexToken
+import com.github.h0tk3y.betterParse.parser.Parser
+import prolog.ast.arithmetic.Float
+import prolog.ast.arithmetic.Integer
+import prolog.ast.terms.Atom
+import prolog.ast.terms.Structure
+import prolog.ast.terms.Term
+import prolog.ast.terms.Variable
+
+open class SimplePrologParser : Grammar<Any>() {
+    // Prolog tokens
+    private val nameToken: Token by regexToken("[a-z][a-zA-Z0-9_]*")
+    private val variableToken: Token by regexToken("[A-Z][a-zA-Z0-9_]*")
+
+    // Arithmetic tokens
+    private val floatToken: Token by regexToken("-?[1-9][0-9]*\\.[0-9]+")
+    private val integerToken: Token by regexToken("-?([1-9][0-9]*|0)")
+
+    // Special tokens
+    private val comma: Token by literalToken(",")
+    private val leftParenthesis: Token by literalToken("(")
+    private val rightParenthesis: Token by literalToken(")")
+
+    // Ignored tokens
+    private val whitespace: Token by regexToken("\\s+", ignore = true)
+    private val singleLineComment: Token by regexToken("%[^\\n]*", ignore = true)
+    private val multiLineComment: Token by regexToken("/\\*.*?\\*/", ignore = true)
+
+    // Prolog parsers
+    private val atomParser: Parser<Atom> by nameToken use { Atom(text) }
+    private val variableParser: Parser<Variable> by variableToken use { Variable(text) }
+    private val structureParser: Parser<Structure> by (atomParser and skip(leftParenthesis) and separated(
+        parser(this::termParser),
+        comma,
+        acceptZero = true
+    ) and skip(rightParenthesis)) use {
+        Structure(t1, t2.terms)
+    }
+
+    // Arithmetic parsers
+    private val integerParser: Parser<Integer> by integerToken use { Integer(text.toInt()) }
+    private val floatParser: Parser<Float> by floatToken use {
+        Float(text.toFloat())
+    }
+
+    private val termParser: Parser<Term> by (floatParser
+            or integerParser
+            or variableParser
+            or structureParser
+            or atomParser
+    ) map { it }
+
+    override val rootParser: Parser<Any> = termParser
+}