Add 29: "Limitations of Language"

Author: janlelis

source/posts/29-limitations-of-language.html.md

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+---
+title: Limitations of Language
+date: 2015-05-29
+tags: syntax, grammar
+---
+
+If you take a closer look, you'll notice that Ruby's grammar has quite a few edge-case where its syntax is inconsistent or ambigious:
+
+ARTICLE
+
+## Binary Minus vs Minus taken as Unary Method Argument
+
+    >> [1,3,4,5].size - 1
+    # => 3
+
+    >> [1,3,4,5].size -1
+    # wrong number of arguments(1 for 0)
+
+## No Simple Rule, if a Symbol can be Displayed Without the Explicit `:""` Syntax
+
+    >> {:< => 0}
+    # => {:<=>0}
+
+    >> {:<=>0}
+    # syntax error, unexpected tINTEGER,
+    # expecting tASSOC
+
+## Different Rules for Modules and Classes
+
+    >> module Eurucamp end
+    # => nil
+
+    >> class Eurucamp end
+    # syntax error, unexpected $end
+
+## Ambiguous if to Parse `~` Unary or as Part of Binary Match Operator
+
+    >> $_="Eurucamp X"
+    >> ~/X/ # => 9
+
+    >> a=~/X/ # undefined local variable or method `a'
+    >> a= ~/X/ # => 9
+
+## Global Variables can "Break" String and Regex Syntax
+
+    >> a = "Eurucamp #\n"
+    >> a.gsub /#$/, ''
+    # => ?
+
+    >> a = "Eurucamp #\n"
+    >> a.gsub /#$/, ''
+    # unterminated regexp meets end of file
+
+    >> a = "Eurucamp #\n"
+    >> a.gsub /#$//, ''
+    # => "Eurucamp #"
+
+## Unary or Binary Plus, Part 2
+
+    >> p = 21
+    >> p 21
+    # => 21
+
+    >> p = 21
+    >> p +21
+    # => 42
+
+## String Creation vs Format Method
+
+    >> puts%[1]
+    # undefined method `%' for nil:NilClass
+
+    >> puts %[1]
+    # => 1
+
+## Regex vs Division
+
+    >> puts /4/i
+    # => (?i-mx:4)
+
+    >> puts, i = 42, 2
+    >> puts /4/i
+    # => 5
+
+## Further Reading
+
+- [Ruby's grammar definition](https://github.com/ruby/ruby/blob/trunk/parse.y)