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diff --git a/docs/doc/assert.html b/docs/doc/assert.html index ceccf72a..d800155f 100644 --- a/docs/doc/assert.html +++ b/docs/doc/assert.html @@ -8,28 +8,35 @@ <p>BQN provides some simple facilities for dealing with errors. Errors are an unusual sort of control flow; if possible, prefer to work with functions that return normally.</p> <h2 id="assert"><a class="header" href="#assert">Assert</a></h2> <p>BQN takes the position that errors exist to indicate exceptional conditions that the developer of a given program didn't expect. However, the types of errors that BQN naturally checks for, such as mismatched shapes in Couple (<code><span class='Function'>≍</span></code>), aren't always enough to detect exceptional conditions. Issues like numeric values that don't make physical sense will slip right through. BQN makes it easy for a programmer to check for these sorts of problems by building in the primitive Assert, written <code><span class='Function'>!</span></code>. This function checks whether <code><span class='Value'>𝕩</span></code> matches <code><span class='Number'>1</span></code>: if it does, then it does nothing and returns <code><span class='Value'>𝕩</span></code>, and otherwise it gives an error.</p> -<a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=ISAyPTIgICMgUGFzc2VkCiEgMj0zICAjIEZhaWxlZA==">↗️</a><pre> <span class='Function'>!</span> <span class='Number'>2</span><span class='Function'>=</span><span class='Number'>2</span> <span class='Comment'># Passed +<a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=ISAyPTIgICMgUGFzc2VkCgohIDI9MyAgIyBGYWlsZWQ=">↗️</a><pre> <span class='Function'>!</span> <span class='Number'>2</span><span class='Function'>=</span><span class='Number'>2</span> <span class='Comment'># Passed </span>1 + <span class='Function'>!</span> <span class='Number'>2</span><span class='Function'>=</span><span class='Number'>3</span> <span class='Comment'># Failed </span><span class='Error'>Error: Assertion error</span> </pre> <p>To pass, the right argument must be exactly the number <code><span class='Number'>1</span></code>; any other value causes an error. For example, an array of <code><span class='Number'>1</span></code>s still causes an error; use <code><span class='Function'>∧</span><span class='Modifier'>´</span><span class='Function'>⥊</span></code> to convert a boolean array to a single boolean that indicates whether all of its values are true.</p> -<a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=ISAo4oinPeKIqOKMvsKsKeKMnMucIOKGlTIKISDiiKfCtOKliiAo4oinPeKIqOKMvsKsKeKMnMucIOKGlTI=">↗️</a><pre> <span class='Function'>!</span> <span class='Paren'>(</span><span class='Function'>∧=∨</span><span class='Modifier2'>⌾</span><span class='Function'>¬</span><span class='Paren'>)</span><span class='Modifier'>⌜˜</span> <span class='Function'>↕</span><span class='Number'>2</span> +<a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=ISAo4oinPeKIqOKMvsKsKeKMnMucIOKGlTIKCiEg4oinwrTipYogKOKIpz3iiKjijL7CrCnijJzLnCDihpUy">↗️</a><pre> <span class='Function'>!</span> <span class='Paren'>(</span><span class='Function'>∧=∨</span><span class='Modifier2'>⌾</span><span class='Function'>¬</span><span class='Paren'>)</span><span class='Modifier'>⌜˜</span> <span class='Function'>↕</span><span class='Number'>2</span> <span class='Error'>Error: 2‿2⥊1‿1‿1‿1</span> + <span class='Function'>!</span> <span class='Function'>∧</span><span class='Modifier'>´</span><span class='Function'>⥊</span> <span class='Paren'>(</span><span class='Function'>∧=∨</span><span class='Modifier2'>⌾</span><span class='Function'>¬</span><span class='Paren'>)</span><span class='Modifier'>⌜˜</span> <span class='Function'>↕</span><span class='Number'>2</span> 1 </pre> -<p>Assert can take a left argument, which gives a message to be associated with the error. It's typical to use a string for the left argument in order to display it to the programmer, but the left argument can be any value.</p> -<a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=Ik1lc3NhZ2UiICEgMArin6jiiJgsImFiYyIsy5zin6kgISAnMCc=">↗️</a><pre> <span class='String'>"Message"</span> <span class='Function'>!</span> <span class='Number'>0</span> +<p>Assert can take a left argument, which gives a message to be associated with the error. It's typical to use a string for <code><span class='Value'>𝕨</span></code> in order to display it to the programmer, but <code><span class='Value'>𝕨</span></code> can be any value.</p> +<a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=Ik1lc3NhZ2UiICEgMAoK4p+o4oiYLCJhYmMiLMuc4p+pICEgJzAn">↗️</a><pre> <span class='String'>"Message"</span> <span class='Function'>!</span> <span class='Number'>0</span> <span class='Error'>Error: Message</span> + <span class='Bracket'>⟨</span><span class='Modifier2'>∘</span><span class='Separator'>,</span><span class='String'>"abc"</span><span class='Separator'>,</span><span class='Modifier'>˜</span><span class='Bracket'>⟩</span> <span class='Function'>!</span> <span class='String'>'0'</span> <span class='Error'>Error: ⟨∘,"abc",˜⟩</span> </pre> +<p>In the 1-argument case, <code><span class='Value'>𝕩</span></code> is used for the error message if it's not <code><span class='Number'>1</span></code>. So an unconditional error can also be written this way:</p> +<a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=ISAiTWVzc2FnZSI=">↗️</a><pre> <span class='Function'>!</span> <span class='String'>"Message"</span> +<span class='Error'>Error: Message</span> +</pre> <h3 id="computing-the-error-message-on-demand"><a class="header" href="#computing-the-error-message-on-demand">Computing the error message on demand</a></h3> <p>Because the left argument to a function is always computed before the function is called, Assert <a href="../commentary/problems.html#assert-has-no-way-to-compute-the-error-message">doesn't let you</a> compute the error message only if there's an error. This might be a problem if the error message computation is slow or has side effects. There are a few ways to work around the issue:</p> <ul> -<li>Handle errors with ordinary if-then logic (perhaps using <a href="control.html">control structures</a>). This is probably the best path for user-facing applications where displaying an error goes through the user interface.</li> -<li>Write a function <code><span class='Function'>Message</span></code> to compute the message, and call <code><span class='Value'>𝕨</span> <span class='Function'>Message</span><span class='Modifier2'>⊸</span><span class='Function'>!</span><span class='Modifier2'>⍟</span><span class='Paren'>(</span><span class='Number'>1</span><span class='Modifier2'>⊸</span><span class='Function'>≢</span><span class='Paren'>)</span> <span class='Value'>𝕩</span></code> or similar instead of <code><span class='Function'>!</span></code>.</li> +<li>Handle bad inputs with ordinary if-then logic (perhaps using <a href="control.html">control structures</a>), not errors. This is probably the best path for user-facing applications where BQN's normal error display isn't wanted.</li> +<li>Write a function <code><span class='Function'>Message</span></code> to compute the message, and call <code><span class='Function'>!</span><span class='Modifier2'>∘</span><span class='Function'>Message</span><span class='Modifier2'>⍟</span><span class='Paren'>(</span><span class='Number'>1</span><span class='Modifier2'>⊸</span><span class='Function'>≢</span><span class='Paren'>)</span> <span class='Value'>𝕩</span></code> or similar instead of <code><span class='Function'>!</span></code>.</li> <li>If the error will be caught elsewhere in the program, use a closure for the message and evaluate it when caught. With a function <code><span class='Function'>Message</span></code> as above, <code><span class='Value'>message</span> <span class='Function'>!</span> <span class='Value'>𝕩</span></code> works, and <code><span class='Brace'>{</span><span class='Value'>…</span><span class='Brace'>}</span><span class='Modifier'>˙</span><span class='Modifier2'>⊸</span><span class='Function'>!</span> <span class='Value'>𝕩</span></code> is a convenient syntax for block functions.</li> </ul> <h2 id="catch"><a class="header" href="#catch">Catch</a></h2> |