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copied!<p>From the <a href="http://www.haskell.org/onlinereport/lexemes.html" rel="nofollow noreferrer">haskell report</a>, this is the syntax for allowed symbols:</p> <p><code>a | b</code> means <code>a or b</code> and </p> <p><code>a<b></code> means <code>a except b</code></p> <pre><code>special -> ( | ) | , | ; | [ | ] | `| { | } symbol -> ascSymbol | uniSymbol<special | _ | : | " | '> ascSymbol -> ! | # | $ | % | & | * | + | . | / | < | = | > | ? | @ \ | ^ | | | - | ~ uniSymbol -> any Unicode symbol or punctuation </code></pre> <p>So, symbols are ascii symbols or unicode symbols except from those in <code>special | _ | : | " | '</code>, which are reserved.</p> <p>so the following can't be used: <code>| , ; [ ] ` { } _ : " '</code></p> <p>A few paragraphs below, the report gives the complete definition for haskell operators:</p> <pre><code>varsym -> ( symbol {symbol | :})<reservedop | dashes> consym -> (: {symbol | :})<reservedop> reservedop -> .. | : | :: | = | \ | | | <- | -> | @ | ~ | => </code></pre> <blockquote> <p>Operator symbols are formed from one or more symbol characters, as defined above, and are lexically distinguished into two namespaces (Section 1.4):</p> <ul> <li>An operator symbol starting with a colon is a constructor.</li> <li>An operator symbol starting with any other character is an ordinary identifier. </li> </ul> <p>Notice that a colon by itself, ":", is reserved solely for use as the Haskell list constructor; this makes its treatment uniform with other parts of list syntax, such as "[]" and "[a,b]".</p> <p>Other than the special syntax for prefix negation, all operators are infix, although each infix operator can be used in a section to yield partially applied operators (see Section 3.5). All of the standard infix operators are just predefined symbols and may be rebound.</p> </blockquote>

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