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Diffstat (limited to 'erlang.html.markdown')
| -rw-r--r-- | erlang.html.markdown | 46 |
1 files changed, 41 insertions, 5 deletions
diff --git a/erlang.html.markdown b/erlang.html.markdown index 8b67a76a..a57f295f 100644 --- a/erlang.html.markdown +++ b/erlang.html.markdown @@ -25,6 +25,7 @@ filename: learnerlang.erl %% 1. Variables and pattern matching. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +% In Erlang new variables are bound with an `=` statement. Num = 42. % All variable names must start with an uppercase letter. % Erlang has single-assignment variables; if you try to assign a different @@ -32,9 +33,11 @@ Num = 42. % All variable names must start with an uppercase letter. Num = 43. % ** exception error: no match of right hand side value 43 % In most languages, `=` denotes an assignment statement. In Erlang, however, -% `=` denotes a pattern-matching operation. `Lhs = Rhs` really means this: -% evaluate the right side (`Rhs`), and then match the result against the -% pattern on the left side (`Lhs`). +% `=` denotes a pattern-matching operation. When an empty variable is used on the +% left hand side of the `=` operator to is bound (assigned), but when a bound +% variable is used on the left hand side the following behaviour is observed. +% `Lhs = Rhs` really means this: evaluate the right side (`Rhs`), and then +% match the result against the pattern on the left side (`Lhs`). Num = 7 * 6. % Floating-point number. @@ -174,7 +177,7 @@ is_dog(A) -> false. % A guard sequence is either a single guard or a series of guards, separated % by semicolons (`;`). The guard sequence `G1; G2; ...; Gn` is true if at % least one of the guards `G1`, `G2`, ..., `Gn` evaluates to `true`. -is_pet(A) when is_atom(A), (A =:= dog) or (A =:= cat) -> true; +is_pet(A) when is_atom(A), (A =:= dog);(A =:= cat) -> true; is_pet(A) -> false. % Warning: not all valid Erlang expressions can be used as guard expressions; @@ -289,7 +292,7 @@ calculateArea() -> _ -> io:format("We can only calculate area of rectangles or circles.") end. - + % Compile the module and create a process that evaluates `calculateArea` in the % shell. c(calculateGeometry). @@ -299,6 +302,39 @@ CalculateArea ! {circle, 2}. % 12.56000000000000049738 % The shell is also a process; you can use `self` to get the current pid. self(). % <0.41.0> +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%% 5. Testing with EUnit +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% + +% Unit tests can be written using EUnits's test generators and assert macros +-module(fib). +-export([fib/1]). +-include_lib("eunit/include/eunit.hrl"). + +fib(0) -> 1; +fib(1) -> 1; +fib(N) when N > 1 -> fib(N-1) + fib(N-2). + +fib_test_() -> + [?_assert(fib(0) =:= 1), + ?_assert(fib(1) =:= 1), + ?_assert(fib(2) =:= 2), + ?_assert(fib(3) =:= 3), + ?_assert(fib(4) =:= 5), + ?_assert(fib(5) =:= 8), + ?_assertException(error, function_clause, fib(-1)), + ?_assert(fib(31) =:= 2178309) + ]. + +% EUnit will automatically export to a test() function to allow running the tests +% in the erlang shell +fib:test() + +% The popular erlang build tool Rebar is also compatible with EUnit +% ``` +% rebar eunit +% ``` + ``` ## References |