Added tests and fixed timestamp handling

cmds/timestamps/input.go

@@ -8,17 +8,19 @@ import (
 )
 
 var basicLexer = lexer.MustSimple([]lexer.SimpleRule{
-	{"Identifier", `[a-zA-Z_][a-zA-Z0-9_]*`},
+	{"Identifier", `[a-z][a-zA-Z0-9_]*`},
 	{"Date", `\d{4}-\d{2}-\d{2}`},
-	{"Timestamp", `\d{4}-\d{2}-\d{2}T?\d{2}:\d{2}:\d{2}Z?`},
-	{"Time", `\d{2}:\d{2}:\d{2}Z?`},
+	{"Time", `\d{2}:\d{2}:\d{2}`},
 	{"Int", `\d+`},
+	{"T", `T`},
+	{"Z", `Z`},
 	{"Whitespace", `[ ]+`},
 })
 
 var parser = participle.MustBuild[Atom](
 	participle.Lexer(basicLexer),
 	participle.Elide("Whitespace"),
+	participle.UseLookahead(2),
 )
 
 func Parse(expr string) (TimeResult, error) {