hcl: start to implement our own lexer and parser

parser/parser.go

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+package parser

parser/token.go

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+package parser
+
+// Token is the set of lexical tokens of the HCL (HashiCorp Configuration Language)
+type Token int
+
+const (
+	// Special tokens
+	ILLEGAL Token = iota
+	EOF
+	COMMENT
+	NEWLINE
+
+	literal_beg
+	IDENT  // literals
+	NUMBER // 12345
+	FLOAT  // 123.45
+	BOOL   // true,false
+	STRING // "abc"
+	literal_end
+
+	operator_beg
+	LBRACK // [
+	LBRACE // {
+	COMMA  // ,
+	PERIOD // .
+
+	RBRACK // ]
+	RBRACE // }
+
+	ASSIGN // =
+	ADD    // +
+	SUB    // -
+
+	EPLUS  // e
+	EMINUS // e-
+	operator_end
+)
+
+// IsLiteral returns true for tokens corresponding to identifiers and basic
+// type literals; it returns false otherwise.
+func (t Token) IsLiteral() bool { return literal_beg < t && t < literal_end }
+
+// IsOperator returns true for tokens corresponding to operators and
+// delimiters; it returns false otherwise.
+func (t Token) IsOperator() bool { return operator_beg < t && t < operator_end }