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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parser.go	c262d2bded §2.8 If/else expressions.	6 年之前
parser_test.go	c262d2bded §2.8 If/else expressions.	6 年之前
parser_tracing.go	c262d2bded §2.8 If/else expressions.	6 年之前