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diff --git a/docs/spec/evaluate.html b/docs/spec/evaluate.html index 6fdf0a0f..2d28eb12 100644 --- a/docs/spec/evaluate.html +++ b/docs/spec/evaluate.html @@ -14,7 +14,7 @@ <p>A block consists of several <code><span class='Function'>BODY</span></code> terms, some of which may have an accompanying header describing accepted inputs and how they are processed. An immediate block <code><span class='Value'>brImm</span></code> can only have one <code><span class='Function'>BODY</span></code>, and is evaluated by evaluating the code in it. Other types of blocks do not evaluate any <code><span class='Function'>BODY</span></code> immediately, but instead return a function or modifier that obtains its result by evaluating a particular <code><span class='Function'>BODY</span></code>. The <code><span class='Function'>BODY</span></code> is identified and evaluated once the block has received enough inputs (operands or arguments), which for modifiers can take one or two calls: if two calls are required, then on the first call the operands are simply stored and no code is evaluated yet. Two calls are required if there is more than one <code><span class='Function'>BODY</span></code> term, if the <code><span class='Function'>BODY</span></code> contains the special names <code><span class='Value'>𝕨𝕩𝕤</span><span class='Function'>𝕎𝕏𝕊</span></code>, or if its header specifies arguments (the header-body combination is a <code><span class='Modifier'>_mCase</span></code> or <code><span class='Modifier2'>_cCase_</span></code>). Otherwise only one is required.</p> <p>To evaluate a block when enough inputs have been received, first the correct case must be identified. To do this, first each special case (<code><span class='Function'>FCase</span></code>, <code><span class='Modifier'>_mCase</span></code>, or <code><span class='Modifier2'>_cCase_</span></code>), excluding <code><span class='Function'>FCase</span></code> nodes containing <code><span class='Function'>UndoHead</span></code>, is checked in order to see if its arguments are strucurally compatible with the given arguments. That is, is <code><span class='Value'>headW</span></code> is a <code><span class='Value'>subject</span></code>, there must be a left argument matching that structure, and if <code><span class='Value'>headX</span></code> is a <code><span class='Value'>subject</span></code>, the right argument must match that structure. This means that <code><span class='Value'>𝕨</span></code> not only matches any left argument but also no argument. The test for compatibility is the same as for multiple assignment described below, except that the header may contain constants, which must match the corresponding part of the given argument. If no special case matches, then an appropriate general case (<code><span class='Function'>FMain</span></code>, <code><span class='Modifier'>_mMain</span></code>, or <code><span class='Modifier2'>_cMain_</span></code>) is used: if there are two, the first is used with no left argument and the second with a left argument; if there are one, it is always used, and if there are none, an error results.</p> <p>The only remaining step before evaluating the <code><span class='Function'>BODY</span></code> is to bind the inputs and other names. Special names are always bound when applicable: <code><span class='Value'>𝕨𝕩𝕤</span></code> if arguments are used, <code><span class='Value'>𝕨</span></code> if there is a left argument, <code><span class='Value'>𝕗𝕘</span></code> if operands are used, and <code><span class='Modifier'>_𝕣</span></code> and <code><span class='Modifier2'>_𝕣_</span></code> for modifiers and combinators, respectively. Any names in the header are also bound, allowing multiple assignment for arguments.</p> -<p>If there is no left argument, but the <code><span class='Function'>BODY</span></code> contains <code><span class='Value'>𝕨</span></code> at the top level, then it is conceptually re-parsed with <code><span class='Value'>𝕨</span></code> replaced by <code><span class='Nothing'>·</span></code> to give a monadic version before application; this modifies the syntax tree by replacing some instances of <code><span class='Value'>arg</span></code> with <code><span class='Value'>nothing</span></code>. However, it also causes an error if, in a function that is called with no left argument, <code><span class='Value'>𝕨</span></code> is used as an operand or list element, where <code><span class='Value'>nothing</span></code> is not allowed by the grammar. The same effect can also be achieved dynamically by treating <code><span class='Nothing'>·</span></code> as a value and checking for it during execution. If it is used as a left argument, then the function should instead be called with no left argument (and similarly in trains); it it is used as a right argument, then the function and its left argument are evaluated but rather than calling the function <code><span class='Nothing'>·</span></code> is "returned" immediately; and if it is used in another context then it causes an error.</p> +<p>If there is no left argument, but the <code><span class='Function'>BODY</span></code> contains <code><span class='Value'>𝕨</span></code> or <code><span class='Function'>𝕎</span></code> at the top level, then it is conceptually re-parsed with <code><span class='Value'>𝕨</span></code> replaced by <code><span class='Nothing'>·</span></code> to give a monadic version before application; this modifies the syntax tree by replacing some instances of <code><span class='Value'>arg</span></code> with <code><span class='Value'>nothing</span></code>. However, it also causes an error if, in a function that is called with no left argument, <code><span class='Value'>𝕨</span></code> is used as an operand or list element, where <code><span class='Value'>nothing</span></code> is not allowed by the grammar. In the case of <code><span class='Function'>𝕎</span></code> it's almost always an error, only valid if used alone in a statement or as the left part of a <code><span class='Function'>Fork</span></code>. True re-parsing is not required as the same effect can also be achieved dynamically by treating <code><span class='Nothing'>·</span></code> as a value and checking for it during execution. If it's used as a left argument, then the function should instead be called with no left argument (and similarly in trains); if it's used as a right argument, then the function and its left argument are evaluated but rather than calling the function <code><span class='Nothing'>·</span></code> is "returned" immediately; and if it's used in another context then it causes an error.</p> <h3 id="assignment">Assignment</h3> <p>An <em>assignment</em> is one of the four rules containing <code><span class='Function'>ASGN</span></code>. It is evaluated by first evaluating the right-hand-side <code><span class='Value'>subExpr</span></code>, <code><span class='Function'>FuncExpr</span></code>, <code><span class='Modifier'>_m1Expr</span></code>, or <code><span class='Modifier2'>_m2Exp_</span></code> expression, and then storing the result in the left-hand-side identifier or identifiers. The result of the assignment expression is the result of its right-hand side. Except for subjects, only a lone identifier is allowed on the left-hand side and storage sets it equal to the result. For subjects, <em>destructuring assignment</em> is performed when an <code><span class='Value'>lhs</span></code> is <code><span class='Value'>lhsList</span></code> or <code><span class='Value'>lhsStr</span></code>. Destructuring assignment is performed recursively by assigning right-hand-side values to the left-hand-side targets, with single-identifier assignment as the base case.</p> <p>The right-hand-side value, here called <code><span class='Value'>v</span></code>, in destructuring assignment must be a list (rank 1 array) or namespace. If it's a list, then each <code><span class='Function'>LHS_ENTRY</span></code> node must be an <code><span class='Function'>LHS_ELT</span></code>. The left-hand side is treated as a list of <code><span class='Value'>lhs</span></code> targets, and matched to <code><span class='Value'>v</span></code> element-wise, with an error if the two lists differ in length. If <code><span class='Value'>v</span></code> is a namespace, then the left-hand side must be an <code><span class='Value'>lhsStr</span></code> where every <code><span class='Function'>LHS_ATOM</span></code> is an <code><span class='Function'>LHS_NAME</span></code>, or an <code><span class='Value'>lhsList</span></code> where every <code><span class='Function'>LHS_ENTRY</span></code> is an <code><span class='Function'>LHS_NAME</span></code> or <code><span class='Value'>lhs</span> <span class='String'>"⇐"</span> <span class='Function'>LHS_NAME</span></code>, so that it can be considered a list of <code><span class='Function'>LHS_NAME</span></code> nodes some of which are also associated with <code><span class='Value'>lhs</span></code> nodes. To perform the assignment, the value of each name is obtained from the namespace <code><span class='Value'>v</span></code>, giving an error if <code><span class='Value'>v</span></code> does not define that name. The value is assigned to the <code><span class='Value'>lhs</span></code> node if present (which may be a destructuring assignment or simple subject assignment), and otherwise assigned to the same <code><span class='Function'>LHS_NAME</span></code> node used to get it from <code><span class='Value'>v</span></code>.</p> diff --git a/spec/evaluate.md b/spec/evaluate.md index 0ad6bf10..90ed32a9 100644 --- a/spec/evaluate.md +++ b/spec/evaluate.md @@ -20,7 +20,7 @@ To evaluate a block when enough inputs have been received, first the correct cas The only remaining step before evaluating the `BODY` is to bind the inputs and other names. Special names are always bound when applicable: `𝕨𝕩𝕤` if arguments are used, `𝕨` if there is a left argument, `𝕗𝕘` if operands are used, and `_𝕣` and `_𝕣_` for modifiers and combinators, respectively. Any names in the header are also bound, allowing multiple assignment for arguments. -If there is no left argument, but the `BODY` contains `𝕨` at the top level, then it is conceptually re-parsed with `𝕨` replaced by `·` to give a monadic version before application; this modifies the syntax tree by replacing some instances of `arg` with `nothing`. However, it also causes an error if, in a function that is called with no left argument, `𝕨` is used as an operand or list element, where `nothing` is not allowed by the grammar. The same effect can also be achieved dynamically by treating `·` as a value and checking for it during execution. If it is used as a left argument, then the function should instead be called with no left argument (and similarly in trains); it it is used as a right argument, then the function and its left argument are evaluated but rather than calling the function `·` is "returned" immediately; and if it is used in another context then it causes an error. +If there is no left argument, but the `BODY` contains `𝕨` or `𝕎` at the top level, then it is conceptually re-parsed with `𝕨` replaced by `·` to give a monadic version before application; this modifies the syntax tree by replacing some instances of `arg` with `nothing`. However, it also causes an error if, in a function that is called with no left argument, `𝕨` is used as an operand or list element, where `nothing` is not allowed by the grammar. In the case of `𝕎` it's almost always an error, only valid if used alone in a statement or as the left part of a `Fork`. True re-parsing is not required as the same effect can also be achieved dynamically by treating `·` as a value and checking for it during execution. If it's used as a left argument, then the function should instead be called with no left argument (and similarly in trains); if it's used as a right argument, then the function and its left argument are evaluated but rather than calling the function `·` is "returned" immediately; and if it's used in another context then it causes an error. ### Assignment |