fgm/waiig15: My version of the Writing an Interpreter in Go 1.5 code.

Frederic G. MARAND c262d2bded §2.8 If/else expressions.		6 年之前
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ast.go	c262d2bded §2.8 If/else expressions.	6 年之前
ast_test.go	d8072da4f9 §2.8: restructured files to match author code more closely.	6 年之前