## 1 Compiler Release Notes History

### 1.1 Compiler 4.3

#### 1.1.1 Fixed Bugs and Malfunctions

- The semantics for boolean operators in guards have been changed to be more consistent.
  All boolean operators will fail if given non-boolean arguments; '`true or garbage`' used to succeed but will now fail. Also, failure in the evaluation of the operands will also cause the guard to fail; '`true or element(1, [])`' used to succeed but will now fail.
  Semicolon will behave as it used to. If a failure as described above occurs, evaluation will continue with the right operand of the semicolon.
  *** POTENTIAL INCOMPATIBILITY ***
  Own Id: OTP-4623
- `-compile(...)` attributes inside an Erlang module can now contain compiler options that control warnings (such as `warn_unused_vars`). They used to be ignored.
  Own Id: OTP-4911
- When a record was updated, and the record given as an expression (such as function call), the record could be evaluated more than once.
  Own Id: OTP-4933
- Compilation of modules with long strings could be extremely slow.
  Own Id: OTP-4960 Aux Id: seq8310
- In bit syntax matching with clauses having guards, sometimes the following clauses would never match if a guard was evaluated (and failed).
  Own Id: OTP-4961 Aux Id: seq8338, OTP-4891
- Using multiple matching ('=') in the pattern for a generator in list comprenhension would cause an internal compiler error.
  Example:

      [3 || {3=4} <- []].

  Own Id: OTP-5076 Aux Id: OTP-5092
- List and string literals, and integer and character literals were not equivalent in matching as they should be. For instance, `f("a"=[$a])` would never match.
  Own Id: OTP-5092 Aux Id: OTP-5076

#### 1.1.2 Improvements and New Features

- The compiler used to warn for definition of functions having the same name as an auto-imported BIF (such as `size/1`). In the R10B release, such warnings will only be emitted if the function is NOT exported (because it will be impossible to call it). Instead, there will be a warning for any local call (call without module prefix) to any (exported) function in the same module that is also the name of an auto-imported BIF. To avoid the warning, insert a module prefix (either `erlang` to call the BIF, or the name of the module to call function in the module).
  Own Id: OTP-4909
- The unary '+' operator has been changed to throw an `badarith` exception if its argument is not numeric (or fail in a guard). It used its argument unchanged whatever the type. Given the new meaning, unary '+' can now be used to test whether a term is numeric.
  *** POTENTIAL INCOMPATIBILITY ***
  Own Id: OTP-4928
- The compiler now warns for more types of suspect code, such as expressions that will fail at run-time (such as `atom-42`), guards that are always false, or patterns that cannot match.
  Own Id: OTP-5098 Aux Id: seq8965, OTP-2456
- The long-awaited `try`...`catch` construction is included in this release. See the reference manual for how to use it.
  Own Id: OTP-5150

### 1.2 Compiler 4.2.3

#### 1.2.1 Fixed Bugs and Malfunctions

- The compiler could generate incorrect code for receive clauses did not use the message in any way, for instance if a guard would ignore message depending on some condition not based on the contents of the message (e.g. a state variable in the "loop data").
  Own Id: OTP-5050

### 1.3 Compiler 4.2.2

#### 1.3.1 Fixed Bugs and Malfunctions

- Compilation of modules with long strings could be extremely slow.
  Own Id: OTP-4960 Aux Id: seq8310
- In bit syntax matching with clauses having guards, sometimes the following clauses would never match if a guard was evaluated (and failed).
  Own Id: OTP-4961 Aux Id: seq8338, OTP-4891
- In `(Expr)#rec{a=A,b=B}`, `Expr` would be evaluated more than once.
  Own Id: OTP-4962 Aux Id: seq8292

### 1.4 Compiler 4.2.1

#### 1.4.1 Improvements and New Features

- In rare circumstances, the compiler could optimize away test that would verify that a tuple or record argument indeed was of the correct type (resulting in an emulator crash if the argument was not of the correct type/size). Wrong code could also be generated for floating point expressions.
  Own Id: OTP-4790

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