Difference between revisions of "Operators"

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(→‎Comparison Operators: Added chaining of ==/!=)
 
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{| class="wikitable"
 
{| class="wikitable"
 
|-
 
|-
! Operator !! Meaning
+
! Operator !! Meaning !! Precedence
 +
|-
 +
| A <c>=</c> B || assignment || 0
 +
|-
 +
| A <c>or</c> B || logical OR: true if either operand is true || 1
 +
|-
 +
| A <c>and</c> B || logical AND: true if both operands are true || 2
 
|-
 
|-
| A <c>=</c> B || assignment
+
| <c>not</c> A || logical negation: true if its operand is false, and vice versa || 3
 
|-
 
|-
| A <c>or</c> B || logical OR: true if either operand is true
+
| A <c>[[isa]]</c> B || type checking || 4
 
|-
 
|-
| A <c>and</c> B || logical AND: true if both operands are true
+
| A <c>==</c> B || equality comparison: true if operands are equal || 5
 
|-
 
|-
| <c>not</c> A || logical negation: true if its operand is false, and vice versa
+
| A <c>!=</c> B || inequality comparison: true if operands are not equal || 5
 
|-
 
|-
| A <c>[[isa]]</c> B || type checking
+
| A <c>></c> B || greater-than comparison || 5
 
|-
 
|-
| A <c>==</c> B || equality comparison: true if operands are equal
+
| A <c><</c> B || less-than comparison || 5
 
|-
 
|-
| A <c>!=</c> B || inequality comparison: true if operands are not equal
+
| A <c>>=</c> B || greater-than or equal-to comparison || 5
 
|-
 
|-
| A <c>></c> B || greater-than comparison
+
| A <c><=</c> B || less-than or equal-to comparison || 5
 
|-
 
|-
| A <c><</c> B || less-than comparison
+
| A <c>+</c> B || addition or concatenation || 6
 
|-
 
|-
| A <c>>=</c> B || greater-than or equal-to comparison
+
| A <c>-</c> B || subtraction or string trimming || 6
 +
|-
 +
| A <c>*</c> B || multiplication or replication || 7
 
|-
 
|-
| A <c><=</c> B || less-than or equal-to comparison
+
| A <c>/</c> B || division or reduction || 7
 
|-
 
|-
| A <c>+</c> B || addition or concatenation
+
| A <c>%</c> B || modulo (remainder) || 7
 
|-
 
|-
| A <c>-</c> B || subtraction or string trimming
+
| <c>-A</c> || unary minus (numeric negation) || 8
 
|-
 
|-
| A <c>*</c> B || multiplication or replication
+
| <c>[[new]]</c> A || instantiation || 9
 
|-
 
|-
| A <c>/</c> B || division or reduction
+
| <c>@</c>A || [[@ operator|address-of]] (reference function without invoking it) || 10
 
|-
 
|-
| <c>-</c>A || unary minus (numeric negation)
+
| A <c>^</c> B || power: A raised to the power of B || 11
 
|-
 
|-
| <c>[[new]]</c> A || instantiation
+
| <c>A[</c>B<c>]</c> || indexing || 12
 
|-
 
|-
| <c>@</c>A || address-of (reference function without invoking it)
+
| <c>A[</c>B<c>:</c>C<c>]</c> || slicing || 12
 
|-
 
|-
| A <c>^</c> B || power: A raised to the power of B
+
| <c>A(</c>B, C...<c>)</c> || [[Function#Calling_a_Function | calling a function]] || 12
 
|-
 
|-
| A<c>.</c>B || [[Dot syntax|dot operator]]
+
| A<c>.</c>B || [[Dot syntax|dot operator]] || 12
 
|}
 
|}
  
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=== Comparison Operators ===
 
=== Comparison Operators ===
  
In the case of comparison operators (<c>></c>, <c><</c>, <c>>=</c> and <c><=</c>), operands are compared in pairs from left to right.  All comparisons must be true for the complete chained expression to be considered true.  The most common use of this is to check whether a variable is in a certain range, with an expression like <c>0 < x < 10</c>, which is true only if <c>x</c> is between 0 and 10 (non-inclusive).
+
In the case of comparison operators (<c>==</c>, <c>!=</c>, <c>></c>, <c><</c>, <c>>=</c> and <c><=</c>), operands are compared in pairs from left to right.  All comparisons must be true for the complete chained expression to be considered true.  The most common use of this is to check whether a variable is in a certain range, with an expression like <c>0 < x < 10</c>, which is true only if <c>x</c> is between 0 and 10 (non-inclusive).
  
 
{| class="wikitable"
 
{| class="wikitable"
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|-
 
|-
 
| <c>0 < x < 10 < y</c> || x = 5; y = 15 || true || x is between 0 and 10, and 10 is less than y
 
| <c>0 < x < 10 < y</c> || x = 5; y = 15 || true || x is between 0 and 10, and 10 is less than y
 +
|-
 +
| <c>0 < x == 5 < y</c> || x = 5; y = 15 || true || <c>0 < x</c> ''and'' <c>x == 5</c> ''and'' <c>5 < y</c>
 
|}
 
|}
  
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MiniScript proceeds in the following steps:
 
MiniScript proceeds in the following steps:
# <c>foo.bar</c> is evaluated by looking up "bar" in </c>foo</c> (and in the event that this references a function, it's invoked with <c>[[self]]</c> bound to <c>foo</c>.
+
# <c>foo.bar</c> is evaluated by looking up "bar" in <c>foo</c> (and in the event that this references a function, it's invoked with <c>[[self]]</c> bound to <c>foo</c>.
 
# <c>.baz</c> is evaluated by looking up "baz" in the result of step 1 (which should be a map). (And if "baz" references a function, it's invoked with <c>[[self]]</c> bound to the map from step 1.)
 
# <c>.baz</c> is evaluated by looking up "baz" in the result of step 1 (which should be a map). (And if "baz" references a function, it's invoked with <c>[[self]]</c> bound to the map from step 1.)
  
 
This can continue for an arbitrarily long chain of dot operators.
 
This can continue for an arbitrarily long chain of dot operators.
 +
 +
== Math-assignment operators ==
 +
 +
In version ''1.6'' the math-assignment operators were added. They overwrite the value of the first operand variable with the result of the operation when performing the operator without assignment.
 +
 +
<ms>
 +
x = 42
 +
x += 13  // x = x + 13
 +
print x  // 55
 +
 +
s = "hello.ms"
 +
s -= ".ms"  // s = s - ".ms"
 +
print s  // "hello"
 +
</ms>
 +
 +
{| class="wikitable"
 +
|-
 +
! Operator !! Meaning
 +
|-
 +
| A <c>+=</c> B || A = A + B
 +
|-
 +
| A <c>-=</c> B || A = A - B
 +
|-
 +
| A <c>*=</c> B || A = A * B
 +
|-
 +
| A <c>/=</c> B || A = A / B
 +
|-
 +
| A <c>%=</c> B || A = A % B
 +
|-
 +
| A <c>^=</c> B || A = A ^ B
 +
|}
 +
 +
== Tricky spaces ==
 +
 +
MiniScript allows an expression to be the entire statement (which is useful in [[REPL]] where it evaluates the expression and immediately prints the result).
 +
 +
<ms>
 +
4 + 5          // REPL prints 9
 +
 +
f = function(x,y)
 +
x + y      // the result is "dropped"
 +
end function
 +
f 4, 5          // prints nothing
 +
 +
</ms>
 +
 +
There are a few cases when using different spacing around operators in such expressions may make MiniScript confuse it with a function call:
 +
 +
<ms>
 +
X[Y]            // Index X with key Y
 +
X [Y]          // Call function X with argument [Y]
 +
 +
X-Y            // Subtract Y from X
 +
X- Y            // Subtract Y from X
 +
X -Y            // Call function X with argument -Y
 +
X - Y          // Subtract Y from X
 +
</ms>
 +
 +
Follow a simple convention to avoid such problems: put spaces around arithmetic operators and if possible don't use a space between an unary operator and its operand.
  
 
[[Category:Language]]
 
[[Category:Language]]

Latest revision as of 21:35, 20 November 2023

MiniScript defines the following operators (listed in order from lowest to highest precedence):

Operator Meaning Precedence
A = B assignment 0
A or B logical OR: true if either operand is true 1
A and B logical AND: true if both operands are true 2
not A logical negation: true if its operand is false, and vice versa 3
A isa B type checking 4
A == B equality comparison: true if operands are equal 5
A != B inequality comparison: true if operands are not equal 5
A > B greater-than comparison 5
A < B less-than comparison 5
A >= B greater-than or equal-to comparison 5
A <= B less-than or equal-to comparison 5
A + B addition or concatenation 6
A - B subtraction or string trimming 6
A * B multiplication or replication 7
A / B division or reduction 7
A % B modulo (remainder) 7
-A unary minus (numeric negation) 8
new A instantiation 9
@A address-of (reference function without invoking it) 10
A ^ B power: A raised to the power of B 11
A[B] indexing 12
A[B:C] slicing 12
A(B, C...) calling a function 12
A.B dot operator 12

Chaining Operators

Most binary operators in MiniScript can be combined into chains, for example 39 + 2 + 1. The details depend on the type of operator:

Arithmetic Operators

In an expression involving a chain of arithmetic operators, the highest-precedent operators are evaluated first, as in standard algebra. You can always use parentheses to break such a chain into smaller chunks, forcing a different evaluation order.

Code Result
2 + 5 * 8 42
(2 + 5) * 8 56
3 ^ 2 + 4 ^ 2 25

Comparison Operators

In the case of comparison operators (==, !=, >, <, >= and <=), operands are compared in pairs from left to right. All comparisons must be true for the complete chained expression to be considered true. The most common use of this is to check whether a variable is in a certain range, with an expression like 0 < x < 10, which is true only if x is between 0 and 10 (non-inclusive).

Code Given Result Read As
0 < x < 10 x = 5 true x is between 0 and 10
0 < x < 10 x = 10 false x is between 0 and 10
0 < x <= 10 x = 10 true x is between 0 and 10 (including 10)
0 < x < 10 < y x = 5; y = 15 true x is between 0 and 10, and 10 is less than y
0 < x == 5 < y x = 5; y = 15 true 0 < x and x == 5 and 5 < y

Dot Operator

A chain of dot operations is evaluated one step at a time left to right.

For example, given the code:

foo.bar.baz

MiniScript proceeds in the following steps:

  1. foo.bar is evaluated by looking up "bar" in foo (and in the event that this references a function, it's invoked with self bound to foo.
  2. .baz is evaluated by looking up "baz" in the result of step 1 (which should be a map). (And if "baz" references a function, it's invoked with self bound to the map from step 1.)

This can continue for an arbitrarily long chain of dot operators.

Math-assignment operators

In version 1.6 the math-assignment operators were added. They overwrite the value of the first operand variable with the result of the operation when performing the operator without assignment.

x = 42
x += 13  // x = x + 13
print x  // 55

s = "hello.ms"
s -= ".ms"  // s = s - ".ms"
print s  // "hello"
Operator Meaning
A += B A = A + B
A -= B A = A - B
A *= B A = A * B
A /= B A = A / B
A %= B A = A % B
A ^= B A = A ^ B

Tricky spaces

MiniScript allows an expression to be the entire statement (which is useful in REPL where it evaluates the expression and immediately prints the result).

4 + 5           // REPL prints 9

f = function(x,y)
	x + y       // the result is "dropped"
end function
f 4, 5          // prints nothing

There are a few cases when using different spacing around operators in such expressions may make MiniScript confuse it with a function call:

X[Y]            // Index X with key Y
X [Y]           // Call function X with argument [Y]

X-Y             // Subtract Y from X
X- Y            // Subtract Y from X
X -Y            // Call function X with argument -Y
X - Y           // Subtract Y from X

Follow a simple convention to avoid such problems: put spaces around arithmetic operators and if possible don't use a space between an unary operator and its operand.